diff --git a/.clang-format b/.clang-format
index dcfd0aad60c31e..86b4fe33e5cd98 100644
--- a/.clang-format
+++ b/.clang-format
@@ -149,7 +149,7 @@ SpaceBeforeCaseColon: false
 #     f();
 #   }
 # }
-SpaceBeforeParens: ControlStatements
+SpaceBeforeParens: ControlStatementsExceptControlMacros
 
 # Don't insert spaces inside empty '()'
 SpaceInEmptyParentheses: false
diff --git a/Documentation/BreakingChanges.adoc b/Documentation/BreakingChanges.adoc
index f8d2eba061c82a..c4985163c3cd5d 100644
--- a/Documentation/BreakingChanges.adoc
+++ b/Documentation/BreakingChanges.adoc
@@ -235,7 +235,7 @@ These features will be removed.
   equivalent `git log --raw`.  We have nominated the command for
   removal, have changed the command to refuse to work unless the
   `--i-still-use-this` option is given, and asked the users to report
-  when they do so.  So far there hasn't been a single complaint.
+  when they do so.
 +
 The command will be removed.
 
diff --git a/Documentation/MyFirstContribution.adoc b/Documentation/MyFirstContribution.adoc
index aca7212cfe2a42..bbb7b45bd4a557 100644
--- a/Documentation/MyFirstContribution.adoc
+++ b/Documentation/MyFirstContribution.adoc
@@ -908,10 +908,13 @@ Now you should be able to go and check out your newly created branch on GitHub.
 === Sending a PR to GitGitGadget
 
 In order to have your code tested and formatted for review, you need to start by
-opening a Pull Request against `gitgitgadget/git`. Head to
-https://github.com/gitgitgadget/git and open a PR either with the "New pull
-request" button or the convenient "Compare & pull request" button that may
-appear with the name of your newly pushed branch.
+opening a Pull Request against either `gitgitgadget/git` or `git/git`. Head to
+https://github.com/gitgitgadget/git or https://github.com/git/git and open a PR
+either with the "New pull request" button or the convenient "Compare & pull
+request" button that may appear with the name of your newly pushed branch.
+
+The differences between using `gitgitgadget/git` and `git/git` as your base can
+be found [here](https://gitgitgadget.github.io/#should-i-use-gitgitgadget-on-gitgitgadgets-git-fork-or-on-gits-github-mirror)
 
 Review the PR's title and description, as they're used by GitGitGadget
 respectively as the subject and body of the cover letter for your change. Refer
diff --git a/Documentation/RelNotes/2.51.1.adoc b/Documentation/RelNotes/2.51.1.adoc
new file mode 100644
index 00000000000000..b8bd49c876be0d
--- /dev/null
+++ b/Documentation/RelNotes/2.51.1.adoc
@@ -0,0 +1,99 @@
+Git 2.51.1 Release Notes
+========================
+
+There shouldn't be anything exciting to see here.  This is primarily
+to flush the "do you still use it?" improvements that has landed on
+the master front, together with a handful of low-hanging, low-impact
+fixes that should be safe.
+
+
+Fixes since Git 2.51.0
+----------------------
+
+ * The "do you still use it?" message given by a command that is
+   deeply deprecated and allow us to suggest alternatives has been
+   updated.
+
+ * The compatObjectFormat extension is used to hide an incomplete
+   feature that is not yet usable for any purpose other than
+   developing the feature further.  Document it as such to discourage
+   its use by mere mortals.
+
+ * Manual page for "gitk" is updated with the current maintainer's
+   name.
+
+ * Update the instructions for using GGG in the MyFirstContribution
+   document to say that a GitHub PR could be made against `git/git`
+   instead of `gitgitgadget/git`.
+
+ * Clang-format update to let our control macros be formatted the way we
+   had them traditionally, e.g., "for_each_string_list_item()" without
+   space before the parentheses.
+
+ * A few places where a size_t value was cast to curl_off_t without
+   checking has been updated to use the existing helper function.
+
+ * The start_delayed_progress() function in the progress eye-candy API
+   did not clear its internal state, making an initial delay value
+   larger than 1 second ineffective, which has been corrected.
+
+ * Makefile tried to run multiple "cargo build" which would not work
+   very well; serialize their execution to work around this problem.
+
+ * Adjust to the way newer versions of cURL selectively enable tracing
+   options, so that our tests can continue to work.
+
+ * During interactive rebase, using 'drop' on a merge commit led to
+   an error, which has been corrected.
+
+ * "git refs migrate" to migrate the reflog entries from a refs
+   backend to another had a handful of bugs squashed.
+
+ * "git push" had a code path that led to BUG() but it should have
+   been a die(), as it is a response to a usual but invalid end-user
+   action to attempt pushing an object that does not exist.
+
+ * Various bugs about rename handling in "ort" merge strategy have
+   been fixed.
+
+ * "git diff --no-index" run inside a subdirectory under control of a
+   Git repository operated at the top of the working tree and stripped
+   the prefix from the output, and oddballs like "-" (stdin) did not
+   work correctly because of it.  Correct the set-up by undoing what
+   the set-up sequence did to cwd and prefix.
+
+ * Various options to "git diff" that make comparison ignore certain
+   aspects of the differences (like "space changes are ignored",
+   "differences in lines that match these regular expressions are
+   ignored") did not work well with "--name-only" and friends.
+
+ * Under a race against another process that is repacking the
+   repository, especially a partially cloned one, "git fetch" may
+   mistakenly think some objects we do have are missing, which has
+   been corrected.
+
+ * "git repack --path-walk" lost objects in some corner cases, which
+   has been corrected.
+   cf. <CABPp-BHFxxGrqKc0m==TjQNjDGdO=H5Rf6EFsf2nfE1=TuraOQ@mail.gmail.com>
+
+ * Fixes multiple crashes around midx write-out codepaths.
+
+ * A broken or malicious "git fetch" can say that it has the same
+   object for many many times, and the upload-pack serving it can
+   exhaust memory storing them redundantly, which has been corrected.
+
+ * A corner case bug in "git log -L..." has been corrected.
+
+ * Some among "git add -p" and friends ignored color.diff and/or
+   color.ui configuration variables, which is an old regression, which
+   has been corrected.
+
+ * "git rebase -i" failed to clean-up the commit log message when the
+   command commits the final one in a chain of "fixup" commands, which
+   has been corrected.
+
+ * Deal more gracefully with directory / file conflicts when the files
+   backend is used for ref storage, by failing only the ones that are
+   involved in the conflict while allowing others.
+
+Also contains various documentation updates, code cleanups and minor fixups.
diff --git a/Documentation/config.adoc b/Documentation/config.adoc
index 32176de1f4d4e6..5f9a41588bd717 100644
--- a/Documentation/config.adoc
+++ b/Documentation/config.adoc
@@ -114,8 +114,7 @@ whose format and meaning depends on the keyword. Supported keywords
 are:
 
 `gitdir`::
-
-	The data that follows the keyword `gitdir:` is used as a glob
+	The data that follows the keyword `gitdir` and a colon is used as a glob
 	pattern. If the location of the .git directory matches the
 	pattern, the include condition is met.
 +
@@ -148,7 +147,7 @@ refer to linkgit:gitignore[5] for details. For convenience:
 	case-insensitively (e.g. on case-insensitive file systems)
 
 `onbranch`::
-	The data that follows the keyword `onbranch:` is taken to be a
+	The data that follows the keyword `onbranch` and a colon is taken to be a
 	pattern with standard globbing wildcards and two additional
 	ones, `**/` and `/**`, that can match multiple path components.
 	If we are in a worktree where the name of the branch that is
@@ -161,8 +160,8 @@ all branches that begin with `foo/`. This is useful if your branches are
 organized hierarchically and you would like to apply a configuration to
 all the branches in that hierarchy.
 
-`hasconfig:remote.*.url:`::
-	The data that follows this keyword is taken to
+`hasconfig:remote.*.url`::
+	The data that follows this keyword and a colon is taken to
 	be a pattern with standard globbing wildcards and two
 	additional ones, `**/` and `/**`, that can match multiple
 	components. The first time this keyword is seen, the rest of
diff --git a/Documentation/config/alias.adoc b/Documentation/config/alias.adoc
index 2c5db0ad8428e8..80ce17d2deb269 100644
--- a/Documentation/config/alias.adoc
+++ b/Documentation/config/alias.adoc
@@ -3,7 +3,8 @@ alias.*::
 	after defining `alias.last = cat-file commit HEAD`, the invocation
 	`git last` is equivalent to `git cat-file commit HEAD`. To avoid
 	confusion and troubles with script usage, aliases that
-	hide existing Git commands are ignored. Arguments are split by
+	hide existing Git commands are ignored except for deprecated
+	commands.  Arguments are split by
 	spaces, the usual shell quoting and escaping are supported.
 	A quote pair or a backslash can be used to quote them.
 +
@@ -38,6 +39,6 @@ it will be treated as a shell command.  For example, defining
 ** A convenient way to deal with this is to write your script
    operations in an inline function that is then called with any
    arguments from the command-line.  For example `alias.cmd = "!c() {
-   echo $1 | grep $2 ; }; c" will correctly execute the prior example.
+   echo $1 | grep $2 ; }; c"` will correctly execute the prior example.
 ** Setting `GIT_TRACE=1` can help you debug the command being run for
    your alias.
diff --git a/Documentation/config/extensions.adoc b/Documentation/config/extensions.adoc
index 9e2f321a6d776f..532456644b770e 100644
--- a/Documentation/config/extensions.adoc
+++ b/Documentation/config/extensions.adoc
@@ -3,8 +3,7 @@ extensions.*::
 	`core.repositoryFormatVersion` is not `1`. See
 	linkgit:gitrepository-layout[5].
 +
---
-compatObjectFormat::
+compatObjectFormat:::
 	Specify a compatibility hash algorithm to use.  The acceptable values
 	are `sha1` and `sha256`.  The value specified must be different from the
 	value of `extensions.objectFormat`.  This allows client level
@@ -14,19 +13,23 @@ compatObjectFormat::
 	compatObjectFormat.  As well as being able to use oids encoded in
 	compatObjectFormat in addition to oids encoded with objectFormat to
 	locally specify objects.
++
+Note that the functionality enabled by this extension is incomplete and subject
+to change.  It currently exists only to allow development and testing of
+the underlying feature and is not designed to be enabled by end users.
 
-noop::
+noop:::
 	This extension does not change git's behavior at all. It is useful only
 	for testing format-1 compatibility.
 +
 For historical reasons, this extension is respected regardless of the
 `core.repositoryFormatVersion` setting.
 
-noop-v1::
+noop-v1:::
 	This extension does not change git's behavior at all. It is useful only
 	for testing format-1 compatibility.
 
-objectFormat::
+objectFormat:::
 	Specify the hash algorithm to use.  The acceptable values are `sha1` and
 	`sha256`.  If not specified, `sha1` is assumed.
 +
@@ -34,7 +37,7 @@ Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1].  Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
-partialClone::
+partialClone:::
 	When enabled, indicates that the repo was created with a partial clone
 	(or later performed a partial fetch) and that the remote may have
 	omitted sending certain unwanted objects.  Such a remote is called a
@@ -46,30 +49,31 @@ The value of this key is the name of the promisor remote.
 For historical reasons, this extension is respected regardless of the
 `core.repositoryFormatVersion` setting.
 
-preciousObjects::
+preciousObjects:::
 	If enabled, indicates that objects in the repository MUST NOT be deleted
 	(e.g., by `git-prune` or `git repack -d`).
 +
 For historical reasons, this extension is respected regardless of the
 `core.repositoryFormatVersion` setting.
 
-refStorage::
+refStorage:::
 	Specify the ref storage format to use. The acceptable values are:
 +
+--
 include::../ref-storage-format.adoc[]
-
+--
 +
 Note that this setting should only be set by linkgit:git-init[1] or
 linkgit:git-clone[1]. Trying to change it after initialization will not
 work and will produce hard-to-diagnose issues.
 
-relativeWorktrees::
+relativeWorktrees:::
 	If enabled, indicates at least one worktree has been linked with
 	relative paths. Automatically set if a worktree has been created or
 	repaired with either the `--relative-paths` option or with the
 	`worktree.useRelativePaths` config set to `true`.
 
-worktreeConfig::
+worktreeConfig:::
 	If enabled, then worktrees will load config settings from the
 	`$GIT_DIR/config.worktree` file in addition to the
 	`$GIT_COMMON_DIR/config` file. Note that `$GIT_COMMON_DIR` and
@@ -83,11 +87,12 @@ When enabling this extension, you must be careful to move
 certain values from the common config file to the main working tree's
 `config.worktree` file, if present:
 +
+--
 * `core.worktree` must be moved from `$GIT_COMMON_DIR/config` to
   `$GIT_COMMON_DIR/config.worktree`.
 * If `core.bare` is true, then it must be moved from `$GIT_COMMON_DIR/config`
   to `$GIT_COMMON_DIR/config.worktree`.
-
+--
 +
 It may also be beneficial to adjust the locations of `core.sparseCheckout`
 and `core.sparseCheckoutCone` depending on your desire for customizable
@@ -100,4 +105,3 @@ details.
 +
 For historical reasons, this extension is respected regardless of the
 `core.repositoryFormatVersion` setting.
---
diff --git a/Documentation/config/log.adoc b/Documentation/config/log.adoc
index 16e00e8d296aa1..f20cc25cd7c3bf 100644
--- a/Documentation/config/log.adoc
+++ b/Documentation/config/log.adoc
@@ -23,14 +23,14 @@ be used.
 	Print out the ref names of any commits that are shown by the log
 	command. Possible values are:
 +
-----
+--
 `short`;; the ref name prefixes `refs/heads/`, `refs/tags/` and
 	`refs/remotes/` are not printed.
 `full`;; the full ref name (including prefix) are printed.
 `auto`;; if the output is going to a terminal,
 	the ref names are shown as if `short` were given, otherwise no ref
 	names are shown.
-----
+--
 +
 This is the same as the `--decorate` option of the `git log`.
 
diff --git a/Documentation/config/mergetool.adoc b/Documentation/config/mergetool.adoc
index 6be506145c150b..7064f5a462cb56 100644
--- a/Documentation/config/mergetool.adoc
+++ b/Documentation/config/mergetool.adoc
@@ -65,7 +65,7 @@ endif::[]
 	During a merge, Git will automatically resolve as many conflicts as
 	possible and write the `$MERGED` file containing conflict markers around
 	any conflicts that it cannot resolve; `$LOCAL` and `$REMOTE` normally
-	are the versions of the file from before Git`s conflict
+	are the versions of the file from before Git's conflict
 	resolution. This flag causes `$LOCAL` and `$REMOTE` to be overwritten so
 	that only the unresolved conflicts are presented to the merge tool. Can
 	be configured per-tool via the `mergetool.<tool>.hideResolved`
diff --git a/Documentation/config/worktree.adoc b/Documentation/config/worktree.adoc
index 5e35c7d018aecd..9e3f84f748c4aa 100644
--- a/Documentation/config/worktree.adoc
+++ b/Documentation/config/worktree.adoc
@@ -15,5 +15,5 @@ worktree.useRelativePaths::
 	different locations or environments. Defaults to "false".
 +
 Note that setting `worktree.useRelativePaths` to "true" implies enabling the
-`extension.relativeWorktrees` config (see linkgit:git-config[1]),
+`extensions.relativeWorktrees` config (see linkgit:git-config[1]),
 thus making it incompatible with older versions of Git.
diff --git a/Documentation/fetch-options.adoc b/Documentation/fetch-options.adoc
index b01372e4b3c659..65f7d1e7c7b435 100644
--- a/Documentation/fetch-options.adoc
+++ b/Documentation/fetch-options.adoc
@@ -1,7 +1,7 @@
 --[no-]all::
 	Fetch all remotes, except for the ones that has the
 	`remote.<name>.skipFetchAll` configuration variable set.
-	This overrides the configuration variable fetch.all`.
+	This overrides the configuration variable `fetch.all`.
 
 -a::
 --append::
diff --git a/Documentation/git-clone.adoc b/Documentation/git-clone.adoc
index 222d558290ed6b..d829206d1b5d9e 100644
--- a/Documentation/git-clone.adoc
+++ b/Documentation/git-clone.adoc
@@ -16,7 +16,7 @@ git clone [--template=<template-directory>]
 	  [--depth <depth>] [--[no-]single-branch] [--[no-]tags]
 	  [--recurse-submodules[=<pathspec>]] [--[no-]shallow-submodules]
 	  [--[no-]remote-submodules] [--jobs <n>] [--sparse] [--[no-]reject-shallow]
-	  [--filter=<filter-spec>] [--also-filter-submodules]] [--] <repository>
+	  [--filter=<filter-spec> [--also-filter-submodules]] [--] <repository>
 	  [<directory>]
 
 DESCRIPTION
diff --git a/Documentation/git-count-objects.adoc b/Documentation/git-count-objects.adoc
index 97f9f1261010f5..eeee6b9f7f4ac0 100644
--- a/Documentation/git-count-objects.adoc
+++ b/Documentation/git-count-objects.adoc
@@ -28,6 +28,8 @@ size: disk space consumed by loose objects, in KiB (unless -H is specified)
 +
 in-pack: the number of in-pack objects
 +
+packs: the number of pack files
++
 size-pack: disk space consumed by the packs, in KiB (unless -H is specified)
 +
 prune-packable: the number of loose objects that are also present in
diff --git a/Documentation/git-fast-import.adoc b/Documentation/git-fast-import.adoc
index 6f9763c11b3cfd..37d8aa3072130e 100644
--- a/Documentation/git-fast-import.adoc
+++ b/Documentation/git-fast-import.adoc
@@ -61,10 +61,10 @@ OPTIONS
 	currently impacts only the `export-marks`, `import-marks`, and
 	`import-marks-if-exists` feature commands.
 +
-	Only enable this option if you trust the program generating the
-	fast-import stream! This option is enabled automatically for
-	remote-helpers that use the `import` capability, as they are
-	already trusted to run their own code.
+Only enable this option if you trust the program generating the
+fast-import stream! This option is enabled automatically for
+remote-helpers that use the `import` capability, as they are
+already trusted to run their own code.
 
 Options for Frontends
 ~~~~~~~~~~~~~~~~~~~~~
@@ -644,7 +644,7 @@ External data format::
 +
 Here usually `<dataref>` must be either a mark reference (`:<idnum>`)
 set by a prior `blob` command, or a full 40-byte SHA-1 of an
-existing Git blob object.  If `<mode>` is `040000`` then
+existing Git blob object.  If `<mode>` is `040000` then
 `<dataref>` must be the full 40-byte SHA-1 of an existing
 Git tree object or a mark reference set with `--import-marks`.
 
diff --git a/Documentation/git-format-patch.adoc b/Documentation/git-format-patch.adoc
index a8b53db9a6635b..a9cf37182e2d85 100644
--- a/Documentation/git-format-patch.adoc
+++ b/Documentation/git-format-patch.adoc
@@ -587,13 +587,19 @@ an external editor to keep Thunderbird from mangling the patches.
 Approach #1 (add-on)
 ^^^^^^^^^^^^^^^^^^^^
 
-Install the Toggle Word Wrap add-on that is available from
-https://addons.mozilla.org/thunderbird/addon/toggle-word-wrap/
-It adds a menu entry "Enable Word Wrap" in the composer's "Options" menu
+Install the Toggle Line Wrap add-on that is available from
+https://addons.thunderbird.net/thunderbird/addon/toggle-line-wrap
+It adds a button "Line Wrap" to the composer's toolbar
 that you can tick off. Now you can compose the message as you otherwise do
 (cut + paste, 'git format-patch' | 'git imap-send', etc), but you have to
 insert line breaks manually in any text that you type.
 
+As a bonus feature, the add-on can detect patch text in the composer
+and warns when line wrapping has not yet been turned off.
+
+The add-on requires a few tweaks of the advanced configuration
+(about:config). These are listed on the download page.
+
 Approach #2 (configuration)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Three steps:
diff --git a/Documentation/git-interpret-trailers.adoc b/Documentation/git-interpret-trailers.adoc
index 82c8780d932f33..fd335fe772ab99 100644
--- a/Documentation/git-interpret-trailers.adoc
+++ b/Documentation/git-interpret-trailers.adoc
@@ -142,8 +142,8 @@ OPTIONS
 	provided with '--if-exists' overrides the `trailer.ifExists` and any
 	applicable `trailer.<keyAlias>.ifExists` configuration variables
 	and applies to all '--trailer' options until the next occurrence of
-	'--if-exists' or '--no-if-exists'. Upon encountering '--no-if-exists, clear the
-	effect of any previous use of '--if-exists, such that the relevant configuration
+	'--if-exists' or '--no-if-exists'. Upon encountering '--no-if-exists', clear the
+	effect of any previous use of '--if-exists', such that the relevant configuration
 	variables are no longer overridden. Possible actions are `addIfDifferent`,
 	`addIfDifferentNeighbor`, `add`, `replace` and `doNothing`.
 
@@ -154,8 +154,8 @@ OPTIONS
 	provided with '--if-missing' overrides the `trailer.ifMissing` and any
 	applicable `trailer.<keyAlias>.ifMissing` configuration variables
 	and applies to all '--trailer' options until the next occurrence of
-	'--if-missing' or '--no-if-missing'. Upon encountering '--no-if-missing,
-	clear the effect of any previous use of '--if-missing, such that the relevant
+	'--if-missing' or '--no-if-missing'. Upon encountering '--no-if-missing',
+	clear the effect of any previous use of '--if-missing', such that the relevant
 	configuration variables are no longer overridden. Possible actions are `doNothing`
 	or `add`.
 
diff --git a/Documentation/git-merge-tree.adoc b/Documentation/git-merge-tree.adoc
index f824eea61f1e06..4e13ed33d6152f 100644
--- a/Documentation/git-merge-tree.adoc
+++ b/Documentation/git-merge-tree.adoc
@@ -78,11 +78,17 @@ OPTIONS
 
 --merge-base=<tree-ish>::
 	Instead of finding the merge-bases for <branch1> and <branch2>,
-	specify a merge-base for the merge, and specifying multiple bases is
-	currently not supported. This option is incompatible with `--stdin`.
+	specify a merge-base for the merge.  This option is incompatible with
+	`--stdin`.
 +
-As the merge-base is provided directly, <branch1> and <branch2> do not need
-to specify commits; trees are enough.
+Specifying multiple bases is currently not supported, which means that when
+merging two branches with more than one merge-base, using this option may
+cause merge results to differ from what `git merge` would compute.  This
+can include potentially losing some changes made on one side of the history
+in the resulting merge.
++
+With this option, since the merge-base is provided directly, <branch1> and
+<branch2> do not need to specify commits; trees are enough.
 
 -X<option>::
 --strategy-option=<option>::
diff --git a/Documentation/git-multi-pack-index.adoc b/Documentation/git-multi-pack-index.adoc
index b6cd0d7f855d5f..85be5b84eb6851 100644
--- a/Documentation/git-multi-pack-index.adoc
+++ b/Documentation/git-multi-pack-index.adoc
@@ -28,7 +28,7 @@ OPTIONS
 --[no-]progress::
 	Turn progress on/off explicitly. If neither is specified, progress is
 	shown if standard error is connected to a terminal. Supported by
-	sub-commands `write`, `verify`, `expire`, and `repack.
+	sub-commands `write`, `verify`, `expire`, and `repack`.
 
 The following subcommands are available:
 
diff --git a/Documentation/git-patch-id.adoc b/Documentation/git-patch-id.adoc
index 1d15fa45d5126f..45da0f27acde47 100644
--- a/Documentation/git-patch-id.adoc
+++ b/Documentation/git-patch-id.adoc
@@ -33,27 +33,30 @@ OPTIONS
 --verbatim::
 	Calculate the patch-id of the input as it is given, do not strip
 	any whitespace.
-
-	This is the default if patchid.verbatim is true.
++
+This is the default if patchid.verbatim is true.
 
 --stable::
 	Use a "stable" sum of hashes as the patch ID. With this option:
-	 - Reordering file diffs that make up a patch does not affect the ID.
-	   In particular, two patches produced by comparing the same two trees
-	   with two different settings for "-O<orderfile>" result in the same
-	   patch ID signature, thereby allowing the computed result to be used
-	   as a key to index some meta-information about the change between
-	   the two trees;
-
-	 - Result is different from the value produced by git 1.9 and older
-	   or produced when an "unstable" hash (see --unstable below) is
-	   configured - even when used on a diff output taken without any use
-	   of "-O<orderfile>", thereby making existing databases storing such
-	   "unstable" or historical patch-ids unusable.
-
-	 - All whitespace within the patch is ignored and does not affect the id.
-
-	This is the default if patchid.stable is set to true.
++
+--
+- Reordering file diffs that make up a patch does not affect the ID.
+  In particular, two patches produced by comparing the same two trees
+  with two different settings for "-O<orderfile>" result in the same
+  patch ID signature, thereby allowing the computed result to be used
+  as a key to index some meta-information about the change between
+  the two trees;
+
+- Result is different from the value produced by git 1.9 and older
+  or produced when an "unstable" hash (see --unstable below) is
+  configured - even when used on a diff output taken without any use
+  of "-O<orderfile>", thereby making existing databases storing such
+  "unstable" or historical patch-ids unusable.
+
+- All whitespace within the patch is ignored and does not affect the id.
+--
++
+This is the default if patchid.stable is set to true.
 
 --unstable::
 	Use an "unstable" hash as the patch ID. With this option,
@@ -61,8 +64,8 @@ OPTIONS
 	by git 1.9 and older and whitespace is ignored.  Users with pre-existing
 	databases storing patch-ids produced by git 1.9 and older (who do not deal
 	with reordered patches) may want to use this option.
-
-	This is the default.
++
+This is the default.
 
 GIT
 ---
diff --git a/Documentation/git-send-email.adoc b/Documentation/git-send-email.adoc
index 5335502d68fc7b..c610909a92cc3e 100644
--- a/Documentation/git-send-email.adoc
+++ b/Documentation/git-send-email.adoc
@@ -521,10 +521,10 @@ edit `~/.gitconfig` to specify your account settings:
 
 ----
 [sendemail]
-	smtpEncryption = tls
+	smtpEncryption = ssl
 	smtpServer = smtp.gmail.com
 	smtpUser = yourname@gmail.com
-	smtpServerPort = 587
+	smtpServerPort = 465
 ----
 
 Gmail does not allow using your regular password for `git send-email`.
@@ -542,10 +542,10 @@ if you want to use `OAUTHBEARER`, edit your `~/.gitconfig` file and add
 
 ----
 [sendemail]
-	smtpEncryption = tls
+	smtpEncryption = ssl
 	smtpServer = smtp.gmail.com
 	smtpUser = yourname@gmail.com
-	smtpServerPort = 587
+	smtpServerPort = 465
 	smtpAuth = OAUTHBEARER
 ----
 
diff --git a/Documentation/git-whatchanged.adoc b/Documentation/git-whatchanged.adoc
index d21484026fe805..436e219b7d0692 100644
--- a/Documentation/git-whatchanged.adoc
+++ b/Documentation/git-whatchanged.adoc
@@ -15,7 +15,7 @@ WARNING
 -------
 `git whatchanged` has been deprecated and is scheduled for removal in
 a future version of Git, as it is merely `git log` with different
-default; `whatchanged` is not even shorter to type than `log --raw`.
+defaults.
 
 DESCRIPTION
 -----------
@@ -24,7 +24,11 @@ Shows commit logs and diff output each commit introduces.
 
 New users are encouraged to use linkgit:git-log[1] instead.  The
 `whatchanged` command is essentially the same as linkgit:git-log[1]
-but defaults to showing the raw format diff output and skipping merges.
+but defaults to showing the raw format diff output and skipping merges:
+
+----
+git log --raw --no-merges
+----
 
 The command is primarily kept for historical reasons; fingers of
 many people who learned Git long before `git log` was invented by
diff --git a/Documentation/git.adoc b/Documentation/git.adoc
index 743b7b00e4d751..ce099e78b8023e 100644
--- a/Documentation/git.adoc
+++ b/Documentation/git.adoc
@@ -219,7 +219,8 @@ If you just want to run git as if it was started in `<path>` then use
 	List commands by group. This is an internal/experimental
 	option and may change or be removed in the future. Supported
 	groups are: builtins, parseopt (builtin commands that use
-	parse-options), main (all commands in libexec directory),
+	parse-options), deprecated (deprecated builtins),
+	main (all commands in libexec directory),
 	others (all other commands in `$PATH` that have git- prefix),
 	list-<category> (see categories in command-list.txt),
 	nohelpers (exclude helper commands), alias and config
@@ -684,7 +685,7 @@ other
 
 `GIT_PROGRESS_DELAY`::
 	A number controlling how many seconds to delay before showing
-	optional progress indicators. Defaults to 2.
+	optional progress indicators. Defaults to 1.
 
 `GIT_EDITOR`::
 	This environment variable overrides `$EDITOR` and `$VISUAL`.
diff --git a/Documentation/gitcredentials.adoc b/Documentation/gitcredentials.adoc
index 3337bb475de4c5..60c2cc4adefd77 100644
--- a/Documentation/gitcredentials.adoc
+++ b/Documentation/gitcredentials.adoc
@@ -150,9 +150,8 @@ pattern in the config file. For example, if you have this in your config file:
 	username = foo
 --------------------------------------
 
-then we will match: both protocols are the same, both hosts are the same, and
-the "pattern" URL does not care about the path component at all. However, this
-context would not match:
+then we will match: both protocols are the same and both hosts are the same.
+However, this context would not match:
 
 --------------------------------------
 [credential "https://kernel.org"]
@@ -166,11 +165,11 @@ match: Git compares the protocols exactly.  However, you may use wildcards in
 the domain name and other pattern matching techniques as with the `http.<URL>.*`
 options.
 
-If the "pattern" URL does include a path component, then this too must match
-exactly: the context `https://example.com/bar/baz.git` will match a config
-entry for `https://example.com/bar/baz.git` (in addition to matching the config
-entry for `https://example.com`) but will not match a config entry for
-`https://example.com/bar`.
+If the "pattern" URL does include a path component, then this must match
+as a prefix path: the context `https://example.com/bar` will match a config
+entry for `https://example.com/bar/baz.git` but will not match a config entry for
+`https://example.com/other/repo.git` or `https://example.com/barry/repo.git`
+(even though it is a string prefix).
 
 
 CONFIGURATION OPTIONS
diff --git a/Documentation/gitk.adoc b/Documentation/gitk.adoc
index 58ce40ddb11ba5..5b34dcd077123f 100644
--- a/Documentation/gitk.adoc
+++ b/Documentation/gitk.adoc
@@ -163,16 +163,16 @@ used by default. If '$XDG_CONFIG_HOME' is not set it defaults to
 
 History
 -------
-Gitk was the first graphical repository browser. It's written in
-tcl/tk.
+Gitk was the first graphical repository browser, written by
+Paul Mackerras in Tcl/Tk.
 
 'gitk' is actually maintained as an independent project, but stable
 versions are distributed as part of the Git suite for the convenience
 of end users.
 
-gitk-git/ comes from Paul Mackerras's gitk project:
+`gitk-git/` comes from Johannes Sixt's gitk project:
 
-	git://ozlabs.org/~paulus/gitk
+	https://github.com/j6t/gitk
 
 SEE ALSO
 --------
diff --git a/Documentation/pretty-formats.adoc b/Documentation/pretty-formats.adoc
index 9ed0417fc811e5..2121e8e1df0507 100644
--- a/Documentation/pretty-formats.adoc
+++ b/Documentation/pretty-formats.adoc
@@ -232,19 +232,21 @@ ref names with custom decorations. The `decorate` string may be followed by a
 colon and zero or more comma-separated options. Option values may contain
 literal formatting codes. These must be used for commas (`%x2C`) and closing
 parentheses (`%x29`), due to their role in the option syntax.
-+
-** `prefix=<value>`: Shown before the list of ref names.  Defaults to "{nbsp}+(+".
+
+** `prefix=<value>`: Shown before the list of ref names.  Defaults to "{nbsp}++(++".
 ** `suffix=<value>`: Shown after the list of ref names.  Defaults to "+)+".
 ** `separator=<value>`: Shown between ref names.  Defaults to "+,+{nbsp}".
 ** `pointer=<value>`: Shown between HEAD and the branch it points to, if any.
-		      Defaults to "{nbsp}+->+{nbsp}".
+		      Defaults to "{nbsp}++->++{nbsp}".
 ** `tag=<value>`: Shown before tag names. Defaults to "`tag:`{nbsp}".
 
 +
+--
 For example, to produce decorations with no wrapping
 or tag annotations, and spaces as separators:
-+
+
 ++%(decorate:prefix=,suffix=,tag=,separator= )++
+--
 
 ++%(describe++`[:<option>,...]`++)++::
 human-readable name, like linkgit:git-describe[1]; empty string for
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 64cbc583353607..13d355766645fa 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-DEF_VER=v2.51.0
+DEF_VER=v2.51.1
 
 LF='
 '
diff --git a/Makefile b/Makefile
index db9f6a20267d0a..1571b9af99c43c 100644
--- a/Makefile
+++ b/Makefile
@@ -889,7 +889,9 @@ BUILT_INS += git-stage$X
 BUILT_INS += git-status$X
 BUILT_INS += git-switch$X
 BUILT_INS += git-version$X
+ifndef WITH_BREAKING_CHANGES
 BUILT_INS += git-whatchanged$X
+endif
 
 # what 'all' will build but not install in gitexecdir
 OTHER_PROGRAMS += git$X
@@ -4008,13 +4010,12 @@ unit-tests: $(UNIT_TEST_PROGS) $(CLAR_TEST_PROG) t/helper/test-tool$X
 	$(MAKE) -C t/ unit-tests
 
 .PHONY: libgit-sys libgit-rs
-libgit-sys libgit-rs:
-	$(QUIET)(\
-		cd contrib/$@ && \
-		cargo build \
-	)
+libgit-sys:
+	$(QUIET)cargo build --manifest-path contrib/libgit-sys/Cargo.toml
+libgit-rs: libgit-sys
+	$(QUIET)cargo build --manifest-path contrib/libgit-rs/Cargo.toml
 ifdef INCLUDE_LIBGIT_RS
-all:: libgit-sys libgit-rs
+all:: libgit-rs
 endif
 
 LIBGIT_PUB_OBJS += contrib/libgit-sys/public_symbol_export.o
diff --git a/RelNotes b/RelNotes
index 48f15770a4abb8..624baf8c5eb711 120000
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes/2.51.0.adoc
\ No newline at end of file
+Documentation/RelNotes/2.51.1.adoc
\ No newline at end of file
diff --git a/builtin/log.c b/builtin/log.c
index c2f8bbf86301a9..1d1e6e9130a7ed 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -543,7 +543,13 @@ int cmd_whatchanged(int argc,
 	cmd_log_init(argc, argv, prefix, &rev, &opt, &cfg);
 
 	if (!cfg.i_still_use_this)
-		you_still_use_that("git whatchanged");
+		you_still_use_that("git whatchanged",
+				   _("\n"
+				     "hint: You can replace 'git whatchanged <opts>' with:\n"
+				     "hint:\tgit log <opts> --raw --no-merges\n"
+				     "hint: Or make an alias:\n"
+				     "hint:\tgit config set --global alias.whatchanged 'log --raw --no-merges'\n"
+				     "\n"));
 
 	if (!rev.diffopt.output_format)
 		rev.diffopt.output_format = DIFF_FORMAT_RAW;
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 53a225625039ea..ff6900b6545a24 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -3774,7 +3774,7 @@ static void show_object_pack_hint(struct object *object, const char *name,
 	enum stdin_packs_mode mode = *(enum stdin_packs_mode *)data;
 	if (mode == STDIN_PACKS_MODE_FOLLOW) {
 		if (object->type == OBJ_BLOB &&
-		    !has_object(the_repository, &object->oid, 0))
+		    !odb_has_object(the_repository->objects, &object->oid, 0))
 			return;
 		add_object_entry(&object->oid, object->type, name, 0);
 	} else {
@@ -4591,8 +4591,8 @@ static int add_objects_by_path(const char *path,
 
 		/* Skip objects that do not exist locally. */
 		if ((exclude_promisor_objects || arg_missing_action != MA_ERROR) &&
-		    oid_object_info_extended(the_repository, oid, &oi,
-					     OBJECT_INFO_FOR_PREFETCH) < 0)
+		    odb_read_object_info_extended(the_repository->objects, oid, &oi,
+						  OBJECT_INFO_FOR_PREFETCH) < 0)
 			continue;
 
 		exclude = is_oid_uninteresting(the_repository, oid);
diff --git a/builtin/pack-redundant.c b/builtin/pack-redundant.c
index fe81c293e3af6f..5d5ae4afa28f50 100644
--- a/builtin/pack-redundant.c
+++ b/builtin/pack-redundant.c
@@ -626,7 +626,7 @@ int cmd_pack_redundant(int argc, const char **argv, const char *prefix UNUSED, s
 	}
 
 	if (!i_still_use_this)
-		you_still_use_that("git pack-redundant");
+		you_still_use_that("git pack-redundant", NULL);
 
 	if (load_all_packs)
 		load_all();
diff --git a/builtin/reflog.c b/builtin/reflog.c
index 296470b17ca014..c8f6b93d60b1e8 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -429,13 +429,13 @@ static int cmd_reflog_write(int argc, const char **argv, const char *prefix,
 	ret = get_oid_hex_algop(argv[1], &old_oid, repo->hash_algo);
 	if (ret)
 		die(_("invalid old object ID: '%s'"), argv[1]);
-	if (!is_null_oid(&old_oid) && !has_object(the_repository, &old_oid, 0))
+	if (!is_null_oid(&old_oid) && !odb_has_object(repo->objects, &old_oid, 0))
 		die(_("old object '%s' does not exist"), argv[1]);
 
 	ret = get_oid_hex_algop(argv[2], &new_oid, repo->hash_algo);
 	if (ret)
 		die(_("invalid new object ID: '%s'"), argv[2]);
-	if (!is_null_oid(&new_oid) && !has_object(the_repository, &new_oid, 0))
+	if (!is_null_oid(&new_oid) && !odb_has_object(repo->objects, &new_oid, 0))
 		die(_("new object '%s' does not exist"), argv[2]);
 
 	message = argv[3];
diff --git a/builtin/survey.c b/builtin/survey.c
index 5df4fee789c266..f40905fb2fd57a 100644
--- a/builtin/survey.c
+++ b/builtin/survey.c
@@ -642,9 +642,9 @@ static void survey_phase_refs(struct survey_context *ctx)
 		switch (item->kind) {
 		case FILTER_REFS_TAGS:
 			ctx->report.refs.tags_nr++;
-			if (oid_object_info(ctx->repo,
-					    &item->objectname,
-					    &size) == OBJ_TAG)
+			if (odb_read_object_info(ctx->repo->objects,
+						 &item->objectname,
+						 &size) == OBJ_TAG)
 				ctx->report.refs.tags_annotated_nr++;
 			break;
 
@@ -711,8 +711,9 @@ static void increment_totals(struct survey_context *ctx,
 		oi.sizep = &object_length;
 		oi.disk_sizep = &disk_sizep;
 
-		if (oid_object_info_extended(ctx->repo, &oids->oid[i],
-					     &oi, oi_flags) < 0) {
+		if (odb_read_object_info_extended(ctx->repo->objects,
+						  &oids->oid[i],
+						  &oi, oi_flags) < 0) {
 			summary->num_missing++;
 		} else {
 			summary->nr++;
diff --git a/ci/install-dependencies.sh b/ci/install-dependencies.sh
index d061a4729339e0..6668c4df849350 100755
--- a/ci/install-dependencies.sh
+++ b/ci/install-dependencies.sh
@@ -61,6 +61,15 @@ ubuntu-*|i386/ubuntu-*|debian-*)
 		libsecret-1-dev libpcre2-dev meson ninja-build pkg-config \
 		${CC_PACKAGE:-${CC:-gcc}} $PYTHON_PACKAGE
 
+	# Starting with Ubuntu 25.10, sudo can now be provided via either
+	# sudo(1) or sudo-rs(1), with the latter being the default. The problem
+	# is that it does not support `--preserve-env` though, which we rely on
+	# in our CI. We thus revert back to the C implementation.
+	if test -f /etc/alternatives/sudo
+	then
+		sudo update-alternatives --set sudo /usr/bin/sudo.ws
+	fi
+
 	case "$distro" in
 	ubuntu-*)
 		mkdir --parents "$CUSTOM_PATH"
diff --git a/compat/lazyload-curl.c b/compat/lazyload-curl.c
index 2f2b2ebc27993e..a6a3f7e3a7aeaa 100644
--- a/compat/lazyload-curl.c
+++ b/compat/lazyload-curl.c
@@ -106,6 +106,9 @@ static curl_global_sslset_type curl_global_sslset_func;
 typedef void (*curl_global_cleanup_type)(void);
 static curl_global_cleanup_type curl_global_cleanup_func;
 
+typedef CURLcode (*curl_global_trace_type)(const char *config);
+static curl_global_trace_type curl_global_trace_func;
+
 typedef struct curl_slist *(*curl_slist_append_type)(struct curl_slist *list, const char *data);
 static curl_slist_append_type curl_slist_append_func;
 
@@ -201,6 +204,7 @@ static void lazy_load_curl(void)
 	curl_global_init_func = (curl_global_init_type)load_function(libcurl, "curl_global_init");
 	curl_global_sslset_func = (curl_global_sslset_type)load_function(libcurl, "curl_global_sslset");
 	curl_global_cleanup_func = (curl_global_cleanup_type)load_function(libcurl, "curl_global_cleanup");
+	curl_global_trace_func = (curl_global_trace_type)load_function(libcurl, "curl_global_trace");
 	curl_slist_append_func = (curl_slist_append_type)load_function(libcurl, "curl_slist_append");
 	curl_slist_free_all_func = (curl_slist_free_all_type)load_function(libcurl, "curl_slist_free_all");
 	curl_easy_strerror_func = (curl_easy_strerror_type)load_function(libcurl, "curl_easy_strerror");
@@ -268,6 +272,12 @@ void curl_global_cleanup(void)
 	curl_global_cleanup_func();
 }
 
+CURLcode curl_global_trace(const char *config)
+{
+	lazy_load_curl();
+	return curl_global_trace_func(config);
+}
+
 struct curl_slist *curl_slist_append(struct curl_slist *list, const char *data)
 {
 	lazy_load_curl();
diff --git a/diff.c b/diff.c
index cb04a9a6f26f5c..187af4f16a0365 100644
--- a/diff.c
+++ b/diff.c
@@ -1357,6 +1357,9 @@ static void emit_diff_symbol_from_struct(struct diff_options *o,
 	int len = eds->len;
 	unsigned flags = eds->flags;
 
+	if (o->dry_run)
+		return;
+
 	switch (s) {
 	case DIFF_SYMBOL_NO_LF_EOF:
 		context = diff_get_color_opt(o, DIFF_CONTEXT);
@@ -4426,7 +4429,7 @@ static void run_external_diff(const struct external_diff *pgm,
 {
 	struct child_process cmd = CHILD_PROCESS_INIT;
 	struct diff_queue_struct *q = &diff_queued_diff;
-	int quiet = !(o->output_format & DIFF_FORMAT_PATCH);
+	int quiet = !(o->output_format & DIFF_FORMAT_PATCH) || o->dry_run;
 	int rc;
 
 	/*
@@ -6876,6 +6879,15 @@ void diff_flush(struct diff_options *options)
 	if (output_format & DIFF_FORMAT_NO_OUTPUT &&
 	    options->flags.exit_with_status &&
 	    options->flags.diff_from_contents) {
+		/*
+		 * run diff_flush_patch for the exit status. setting
+		 * options->file to /dev/null should be safe, because we
+		 * aren't supposed to produce any output anyway.
+		 */
+		diff_free_file(options);
+		options->file = xfopen("/dev/null", "w");
+		options->close_file = 1;
+		options->color_moved = 0;
 		for (i = 0; i < q->nr; i++) {
 			struct diff_filepair *p = q->queue[i];
 			if (check_pair_status(p))
diff --git a/git-compat-util.h b/git-compat-util.h
index 674d51481bf1a4..3d1f978d984749 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -487,7 +487,7 @@ void warning_errno(const char *err, ...) __attribute__((format (printf, 1, 2)));
 
 void show_usage_if_asked(int ac, const char **av, const char *err);
 
-NORETURN void you_still_use_that(const char *command_name);
+NORETURN void you_still_use_that(const char *command_name, const char *hint);
 
 #ifndef NO_OPENSSL
 #ifdef APPLE_COMMON_CRYPTO
diff --git a/git-curl-compat.h b/git-curl-compat.h
index 04496113fb7b83..ecc2e742922313 100644
--- a/git-curl-compat.h
+++ b/git-curl-compat.h
@@ -53,6 +53,13 @@
 #define GIT_CURL_HAVE_CURLOPT_PROTOCOLS_STR 1
 #endif
 
+/**
+ * curl_global_trace() was added in 8.3.0, released September 2023.
+ */
+#if LIBCURL_VERSION_NUM >= 0x080300
+#define GIT_CURL_HAVE_GLOBAL_TRACE 1
+#endif
+
 /**
  * CURLOPT_TCP_KEEPCNT was added in 8.9.0, released in July, 2024.
  */
diff --git a/git.c b/git.c
index ac75336f5ff07a..5e862ea693d11c 100644
--- a/git.c
+++ b/git.c
@@ -28,6 +28,7 @@
 #define NEED_WORK_TREE		(1<<3)
 #define DELAY_PAGER_CONFIG	(1<<4)
 #define NO_PARSEOPT		(1<<5) /* parse-options is not used */
+#define DEPRECATED		(1<<6)
 
 struct cmd_struct {
 	const char *cmd;
@@ -51,7 +52,9 @@ const char git_more_info_string[] =
 
 static int use_pager = -1;
 
-static void list_builtins(struct string_list *list, unsigned int exclude_option);
+static void list_builtins(struct string_list *list,
+			  unsigned int include_option,
+			  unsigned int exclude_option);
 
 static void exclude_helpers_from_list(struct string_list *list)
 {
@@ -88,7 +91,7 @@ static int list_cmds(const char *spec)
 		int len = sep - spec;
 
 		if (match_token(spec, len, "builtins"))
-			list_builtins(&list, 0);
+			list_builtins(&list, 0, 0);
 		else if (match_token(spec, len, "main"))
 			list_all_main_cmds(&list);
 		else if (match_token(spec, len, "others"))
@@ -99,6 +102,8 @@ static int list_cmds(const char *spec)
 			list_aliases(&list);
 		else if (match_token(spec, len, "config"))
 			list_cmds_by_config(&list);
+		else if (match_token(spec, len, "deprecated"))
+			list_builtins(&list, DEPRECATED, 0);
 		else if (len > 5 && !strncmp(spec, "list-", 5)) {
 			struct strbuf sb = STRBUF_INIT;
 
@@ -322,7 +327,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 			if (!strcmp(cmd, "parseopt")) {
 				struct string_list list = STRING_LIST_INIT_DUP;
 
-				list_builtins(&list, NO_PARSEOPT);
+				list_builtins(&list, 0, NO_PARSEOPT);
 				for (size_t i = 0; i < list.nr; i++)
 					printf("%s ", list.items[i].string);
 				string_list_clear(&list, 0);
@@ -360,7 +365,7 @@ static int handle_options(const char ***argv, int *argc, int *envchanged)
 	return (*argv) - orig_argv;
 }
 
-static int handle_alias(struct strvec *args)
+static int handle_alias(struct strvec *args, struct string_list *expanded_aliases)
 {
 	int envchanged = 0, ret = 0, saved_errno = errno;
 	int count, option_count;
@@ -371,6 +376,8 @@ static int handle_alias(struct strvec *args)
 	alias_command = args->v[0];
 	alias_string = alias_lookup(alias_command);
 	if (alias_string) {
+		struct string_list_item *seen;
+
 		if (args->nr == 2 && !strcmp(args->v[1], "-h"))
 			fprintf_ln(stderr, _("'%s' is aliased to '%s'"),
 				   alias_command, alias_string);
@@ -418,6 +425,25 @@ static int handle_alias(struct strvec *args)
 		if (!strcmp(alias_command, new_argv[0]))
 			die(_("recursive alias: %s"), alias_command);
 
+		string_list_append(expanded_aliases, alias_command);
+		seen = unsorted_string_list_lookup(expanded_aliases,
+						   new_argv[0]);
+
+		if (seen) {
+			struct strbuf sb = STRBUF_INIT;
+			for (size_t i = 0; i < expanded_aliases->nr; i++) {
+				struct string_list_item *item = &expanded_aliases->items[i];
+
+				strbuf_addf(&sb, "\n  %s", item->string);
+				if (item == seen)
+					strbuf_addstr(&sb, " <==");
+				else if (i == expanded_aliases->nr - 1)
+					strbuf_addstr(&sb, " ==>");
+			}
+			die(_("alias loop detected: expansion of '%s' does"
+			      " not terminate:%s"), expanded_aliases->items[0].string, sb.buf);
+		}
+
 		trace_argv_printf(new_argv,
 				  "trace: alias expansion: %s =>",
 				  alias_command);
@@ -590,7 +616,7 @@ static struct cmd_struct commands[] = {
 	{ "notes", cmd_notes, RUN_SETUP },
 	{ "pack-objects", cmd_pack_objects, RUN_SETUP },
 #ifndef WITH_BREAKING_CHANGES
-	{ "pack-redundant", cmd_pack_redundant, RUN_SETUP | NO_PARSEOPT },
+	{ "pack-redundant", cmd_pack_redundant, RUN_SETUP | NO_PARSEOPT | DEPRECATED },
 #endif
 	{ "pack-refs", cmd_pack_refs, RUN_SETUP },
 	{ "patch-id", cmd_patch_id, RUN_SETUP_GENTLY | NO_PARSEOPT },
@@ -648,7 +674,7 @@ static struct cmd_struct commands[] = {
 	{ "verify-tag", cmd_verify_tag, RUN_SETUP },
 	{ "version", cmd_version },
 #ifndef WITH_BREAKING_CHANGES
-	{ "whatchanged", cmd_whatchanged, RUN_SETUP },
+	{ "whatchanged", cmd_whatchanged, RUN_SETUP | DEPRECATED },
 #endif
 	{ "worktree", cmd_worktree, RUN_SETUP },
 	{ "write-tree", cmd_write_tree, RUN_SETUP },
@@ -669,11 +695,16 @@ int is_builtin(const char *s)
 	return !!get_builtin(s);
 }
 
-static void list_builtins(struct string_list *out, unsigned int exclude_option)
+static void list_builtins(struct string_list *out,
+			  unsigned int include_option,
+			  unsigned int exclude_option)
 {
+	if (include_option && exclude_option)
+		BUG("'include_option' and 'exclude_option' are mutually exclusive");
 	for (size_t i = 0; i < ARRAY_SIZE(commands); i++) {
-		if (exclude_option &&
-		    (commands[i].option & exclude_option))
+		if (include_option && !(commands[i].option & include_option))
+			continue;
+		if (exclude_option && (commands[i].option & exclude_option))
 			continue;
 		string_list_append(out, commands[i].cmd);
 	}
@@ -794,13 +825,29 @@ static void execv_dashed_external(const char **argv)
 		exit(128);
 }
 
+static int is_deprecated_command(const char *cmd)
+{
+	struct cmd_struct *builtin = get_builtin(cmd);
+	return builtin && (builtin->option & DEPRECATED);
+}
+
 static int run_argv(struct strvec *args)
 {
 	int done_alias = 0;
-	struct string_list cmd_list = STRING_LIST_INIT_DUP;
-	struct string_list_item *seen;
+	struct string_list expanded_aliases = STRING_LIST_INIT_DUP;
 
 	while (1) {
+		/*
+		 * Allow deprecated commands to be overridden by aliases. This
+		 * creates a seamless path forward for people who want to keep
+		 * using the name after it is gone, but want to skip the
+		 * deprecation complaint in the meantime.
+		 */
+		if (is_deprecated_command(args->v[0]) &&
+		    handle_alias(args, &expanded_aliases)) {
+			done_alias = 1;
+			continue;
+		}
 		/*
 		 * If we tried alias and futzed with our environment,
 		 * it no longer is safe to invoke builtins directly in
@@ -850,35 +897,17 @@ static int run_argv(struct strvec *args)
 		/* .. then try the external ones */
 		execv_dashed_external(args->v);
 
-		seen = unsorted_string_list_lookup(&cmd_list, args->v[0]);
-		if (seen) {
-			struct strbuf sb = STRBUF_INIT;
-			for (size_t i = 0; i < cmd_list.nr; i++) {
-				struct string_list_item *item = &cmd_list.items[i];
-
-				strbuf_addf(&sb, "\n  %s", item->string);
-				if (item == seen)
-					strbuf_addstr(&sb, " <==");
-				else if (i == cmd_list.nr - 1)
-					strbuf_addstr(&sb, " ==>");
-			}
-			die(_("alias loop detected: expansion of '%s' does"
-			      " not terminate:%s"), cmd_list.items[0].string, sb.buf);
-		}
-
-		string_list_append(&cmd_list, args->v[0]);
-
 		/*
 		 * It could be an alias -- this works around the insanity
 		 * of overriding "git log" with "git show" by having
 		 * alias.log = show
 		 */
-		if (!handle_alias(args))
+		if (!handle_alias(args, &expanded_aliases))
 			break;
 		done_alias = 1;
 	}
 
-	string_list_clear(&cmd_list, 0);
+	string_list_clear(&expanded_aliases, 0);
 
 	return done_alias;
 }
diff --git a/http.c b/http.c
index 361c8ba5948f69..18508dd7f41068 100644
--- a/http.c
+++ b/http.c
@@ -1384,6 +1384,14 @@ void http_init(struct remote *remote, const char *url, int proactive_auth)
 	if (curl_global_init(CURL_GLOBAL_ALL) != CURLE_OK)
 		die("curl_global_init failed");
 
+#ifdef GIT_CURL_HAVE_GLOBAL_TRACE
+	{
+		const char *comp = getenv("GIT_TRACE_CURL_COMPONENTS");
+		if (comp)
+			curl_global_trace(comp);
+	}
+#endif
+
 	if (proactive_auth && http_proactive_auth == PROACTIVE_AUTH_NONE)
 		http_proactive_auth = PROACTIVE_AUTH_IF_CREDENTIALS;
 
diff --git a/object-name.c b/object-name.c
index 11aa0e6afc565e..ffd946116d0736 100644
--- a/object-name.c
+++ b/object-name.c
@@ -696,10 +696,9 @@ static inline char get_hex_char_from_oid(const struct object_id *oid,
 		return hex[oid->hash[pos >> 1] & 0xf];
 }
 
-static int extend_abbrev_len(const struct object_id *oid, void *cb_data)
+static int extend_abbrev_len(const struct object_id *oid,
+			     struct min_abbrev_data *mad)
 {
-	struct min_abbrev_data *mad = cb_data;
-
 	unsigned int i = mad->init_len;
 	while (mad->hex[i] && mad->hex[i] == get_hex_char_from_oid(oid, i))
 		i++;
diff --git a/odb.h b/odb.h
index 3dfc66d75a3d20..e8b9dff9480ded 100644
--- a/odb.h
+++ b/odb.h
@@ -475,37 +475,4 @@ static inline int odb_write_object(struct object_database *odb,
 	return odb_write_object_ext(odb, buf, len, type, oid, NULL, 0);
 }
 
-/* Compatibility wrappers, to be removed once Git 2.51 has been released. */
-#include "repository.h"
-
-static inline int oid_object_info_extended(struct repository *r,
-					   const struct object_id *oid,
-					   struct object_info *oi,
-					   unsigned flags)
-{
-	return odb_read_object_info_extended(r->objects, oid, oi, flags);
-}
-
-static inline int oid_object_info(struct repository *r,
-				  const struct object_id *oid,
-				  unsigned long *sizep)
-{
-	return odb_read_object_info(r->objects, oid, sizep);
-}
-
-static inline void *repo_read_object_file(struct repository *r,
-					  const struct object_id *oid,
-					  enum object_type *type,
-					  unsigned long *size)
-{
-	return odb_read_object(r->objects, oid, type, size);
-}
-
-static inline int has_object(struct repository *r,
-			     const struct object_id *oid,
-			     unsigned flags)
-{
-	return odb_has_object(r->objects, oid, flags);
-}
-
 #endif /* ODB_H */
diff --git a/pack-objects.c b/pack-objects.c
index a9d9855063aea8..7b86ae89989800 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -4,6 +4,7 @@
 #include "pack-objects.h"
 #include "packfile.h"
 #include "parse.h"
+#include "repository.h"
 
 static uint32_t locate_object_entry_hash(struct packing_data *pdata,
 					 const struct object_id *oid,
diff --git a/progress.c b/progress.c
index 8d5ae70f3a9ec7..8315bdc3d4a77a 100644
--- a/progress.c
+++ b/progress.c
@@ -114,16 +114,19 @@ static void display(struct progress *progress, uint64_t n, const char *done)
 	const char *tp;
 	struct strbuf *counters_sb = &progress->counters_sb;
 	int show_update = 0;
+	int update = !!progress_update;
 	int last_count_len = counters_sb->len;
 
-	if (progress->delay && (!progress_update || --progress->delay))
+	progress_update = 0;
+
+	if (progress->delay && (!update || --progress->delay))
 		return;
 
 	progress->last_value = n;
 	tp = (progress->throughput) ? progress->throughput->display.buf : "";
 	if (progress->total) {
 		unsigned percent = n * 100 / progress->total;
-		if (percent != progress->last_percent || progress_update) {
+		if (percent != progress->last_percent || update) {
 			progress->last_percent = percent;
 
 			strbuf_reset(counters_sb);
@@ -133,7 +136,7 @@ static void display(struct progress *progress, uint64_t n, const char *done)
 				    tp);
 			show_update = 1;
 		}
-	} else if (progress_update) {
+	} else if (update) {
 		strbuf_reset(counters_sb);
 		strbuf_addf(counters_sb, "%"PRIuMAX"%s", (uintmax_t)n, tp);
 		show_update = 1;
@@ -166,7 +169,6 @@ static void display(struct progress *progress, uint64_t n, const char *done)
 			}
 			fflush(stderr);
 		}
-		progress_update = 0;
 	}
 }
 
@@ -281,7 +283,7 @@ static int get_default_delay(void)
 	static int delay_in_secs = -1;
 
 	if (delay_in_secs < 0)
-		delay_in_secs = git_env_ulong("GIT_PROGRESS_DELAY", 2);
+		delay_in_secs = git_env_ulong("GIT_PROGRESS_DELAY", 1);
 
 	return delay_in_secs;
 }
diff --git a/t/Makefile b/t/Makefile
index 757674e727348c..ab8a5b54aa6ce0 100644
--- a/t/Makefile
+++ b/t/Makefile
@@ -189,15 +189,9 @@ perf:
 
 .PHONY: libgit-sys-test libgit-rs-test
 libgit-sys-test:
-	$(QUIET)(\
-		cd ../contrib/libgit-sys && \
-		cargo test \
-	)
-libgit-rs-test:
-	$(QUIET)(\
-		cd ../contrib/libgit-rs && \
-		cargo test \
-	)
+	$(QUIET)cargo test --manifest-path ../contrib/libgit-sys/Cargo.toml
+libgit-rs-test: libgit-sys-test
+	$(QUIET)cargo test --manifest-path ../contrib/libgit-rs/Cargo.toml
 ifdef INCLUDE_LIBGIT_RS
-all:: libgit-sys-test libgit-rs-test
+all:: libgit-rs-test
 endif
diff --git a/t/helper/test-pack-deltas.c b/t/helper/test-pack-deltas.c
index 4caa024b1ebe73..4981401eaa6664 100644
--- a/t/helper/test-pack-deltas.c
+++ b/t/helper/test-pack-deltas.c
@@ -51,16 +51,14 @@ static void write_ref_delta(struct hashfile *f,
 	unsigned long size, base_size, delta_size, compressed_size, hdrlen;
 	enum object_type type;
 	void *base_buf, *delta_buf;
-	void *buf = repo_read_object_file(the_repository,
-					  oid, &type,
-					  &size);
+	void *buf = odb_read_object(the_repository->objects,
+				    oid, &type, &size);
 
 	if (!buf)
 		die("unable to read %s", oid_to_hex(oid));
 
-	base_buf = repo_read_object_file(the_repository,
-					 base, &type,
-					 &base_size);
+	base_buf = odb_read_object(the_repository->objects,
+				   base, &type, &base_size);
 
 	if (!base_buf)
 		die("unable to read %s", oid_to_hex(base));
diff --git a/t/t0014-alias.sh b/t/t0014-alias.sh
index 56d70b73e1c165..ee0f0a54b6623f 100755
--- a/t/t0014-alias.sh
+++ b/t/t0014-alias.sh
@@ -27,6 +27,20 @@ test_expect_success 'looping aliases - internal execution' '
 	test_grep "^fatal: alias loop detected: expansion of" output
 '
 
+test_expect_success 'looping aliases - deprecated builtins' '
+	test_config alias.whatchanged pack-redundant &&
+	test_config alias.pack-redundant whatchanged &&
+	cat >expect <<-EOF &&
+	${SQ}whatchanged${SQ} is aliased to ${SQ}pack-redundant${SQ}
+	${SQ}pack-redundant${SQ} is aliased to ${SQ}whatchanged${SQ}
+	fatal: alias loop detected: expansion of ${SQ}whatchanged${SQ} does not terminate:
+	  whatchanged <==
+	  pack-redundant ==>
+	EOF
+	test_must_fail git whatchanged -h 2>actual &&
+	test_cmp expect actual
+'
+
 # This test is disabled until external loops are fixed, because would block
 # the test suite for a full minute.
 #
@@ -55,4 +69,47 @@ test_expect_success 'tracing a shell alias with arguments shows trace of prepare
 	test_cmp expect actual
 '
 
+can_alias_deprecated_builtin () {
+	cmd="$1" &&
+	# some git(1) commands will fail for `-h` (the case for
+	# git-status as of 2025-09-07)
+	test_might_fail git status -h >expect &&
+	test_file_not_empty expect &&
+	test_might_fail git -c alias."$cmd"=status "$cmd" -h >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'can alias-shadow deprecated builtins' '
+	for cmd in $(git --list-cmds=deprecated)
+	do
+		can_alias_deprecated_builtin "$cmd" || return 1
+	done
+'
+
+test_expect_success 'can alias-shadow via two deprecated builtins' '
+	# some git(1) commands will fail... (see above)
+	test_might_fail git status -h >expect &&
+	test_file_not_empty expect &&
+	test_might_fail git -c alias.whatchanged=pack-redundant \
+		-c alias.pack-redundant=status whatchanged -h >actual &&
+	test_cmp expect actual
+'
+
+cannot_alias_regular_builtin () {
+	cmd="$1" &&
+	# some git(1) commands will fail... (see above)
+	test_might_fail git "$cmd" -h >expect &&
+	test_file_not_empty expect &&
+	test_might_fail git -c alias."$cmd"=status "$cmd" -h >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success 'cannot alias-shadow a sample of regular builtins' '
+	for cmd in grep check-ref-format interpret-trailers \
+		checkout-index fast-import diagnose rev-list prune
+	do
+		cannot_alias_regular_builtin "$cmd" || return 1
+	done
+'
+
 test_done
diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh
index 3256acaa3505ef..e740ce362988a5 100755
--- a/t/t0300-credentials.sh
+++ b/t/t0300-credentials.sh
@@ -991,18 +991,24 @@ test_expect_success 'url parser not confused by encoded markers' '
 
 test_expect_success 'credential config with partial URLs' '
 	echo "echo password=yep" | write_script git-credential-yep &&
-	test_write_lines url=https://user@example.com/repo.git >stdin &&
+	test_write_lines url=https://user@example.com/org/repo.git >stdin &&
 	for partial in \
 		example.com \
+		example.com/org/repo.git \
 		user@example.com \
+		user@example.com/org/repo.git \
 		https:// \
 		https://example.com \
 		https://example.com/ \
+		https://example.com/org \
+		https://example.com/org/ \
+		https://example.com/org/repo.git \
 		https://user@example.com \
 		https://user@example.com/ \
-		https://example.com/repo.git \
-		https://user@example.com/repo.git \
-		/repo.git
+		https://user@example.com/org \
+		https://user@example.com/org/ \
+		https://user@example.com/org/repo.git \
+		/org/repo.git
 	do
 		git -c credential.$partial.helper=yep \
 			credential fill <stdin >stdout &&
@@ -1012,7 +1018,12 @@ test_expect_success 'credential config with partial URLs' '
 
 	for partial in \
 		dont.use.this \
+		example.com/o \
+		user@example.com/o \
 		http:// \
+		https://example.com/o \
+		https://user@example.com/o \
+		/o \
 		/repo
 	do
 		git -c credential.$partial.helper=yep \
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index cfeec239e0946c..3a47b2f7cbae73 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -661,6 +661,27 @@ test_expect_success 'diff -I<regex>: ignore matching file' '
 	test_grep ! "file1" actual
 '
 
+test_expect_success 'diff -I<regex>: ignore all content changes' '
+	test_when_finished "git rm -f file1 file2" &&
+	: >file1 &&
+	git add file1 &&
+	: >file2 &&
+	git add file2 &&
+
+	rm -f file1 file2 &&
+	mkdir file2 &&
+	test_diff_no_content_changes () {
+		git diff $1 --ignore-blank-lines -I".*" >actual &&
+		test_line_count = 2 actual &&
+		test_grep "file1" actual &&
+		test_grep "file2" actual &&
+		test_grep ! "diff --git" actual
+	} &&
+	test_diff_no_content_changes "--raw" &&
+	test_diff_no_content_changes "--name-only" &&
+	test_diff_no_content_changes "--name-status"
+'
+
 # check_prefix <patch> <src> <dst>
 # check only lines with paths to avoid dependency on exact oid/contents
 check_prefix () {
diff --git a/t/t4035-diff-quiet.sh b/t/t4035-diff-quiet.sh
index 0352bf81a90a38..35eaf0855f86a5 100755
--- a/t/t4035-diff-quiet.sh
+++ b/t/t4035-diff-quiet.sh
@@ -50,6 +50,10 @@ test_expect_success 'git diff-tree HEAD HEAD' '
 	test_expect_code 0 git diff-tree --quiet HEAD HEAD >cnt &&
 	test_line_count = 0 cnt
 '
+test_expect_success 'git diff-tree -w HEAD^ HEAD' '
+	test_expect_code 1 git diff-tree --quiet -w HEAD^ HEAD >cnt &&
+	test_line_count = 0 cnt
+'
 test_expect_success 'git diff-files' '
 	test_expect_code 0 git diff-files --quiet >cnt &&
 	test_line_count = 0 cnt
diff --git a/t/t5564-http-proxy.sh b/t/t5564-http-proxy.sh
index b27e481f95bc4d..c3903faf2d3e6f 100755
--- a/t/t5564-http-proxy.sh
+++ b/t/t5564-http-proxy.sh
@@ -72,7 +72,9 @@ test_expect_success SOCKS_PROXY 'clone via Unix socket' '
 	test_when_finished "rm -rf clone" &&
 	test_config_global http.proxy "socks4://localhost$PWD/%2530.sock" && {
 		{
-			GIT_TRACE_CURL=$PWD/trace git clone "$HTTPD_URL/smart/repo.git" clone 2>err &&
+			GIT_TRACE_CURL=$PWD/trace \
+			GIT_TRACE_CURL_COMPONENTS=socks \
+			git clone "$HTTPD_URL/smart/repo.git" clone 2>err &&
 			grep -i "SOCKS4 request granted" trace
 		} ||
 		old_libcurl_error err
diff --git a/t/t6137-pathspec-wildcards-literal.sh b/t/t6137-pathspec-wildcards-literal.sh
index 20abad5667df28..17a03085ef396d 100755
--- a/t/t6137-pathspec-wildcards-literal.sh
+++ b/t/t6137-pathspec-wildcards-literal.sh
@@ -3,8 +3,8 @@ test_description='test wildcards and literals with git add/commit (subshell styl
 
 . ./test-lib.sh
 
-test_have_prereq FUNNYNAMES || {
-	skip_all='skipping: needs FUNNYNAMES (non-Windows only)'
+test_have_prereq BSLASHPSPEC || {
+	skip_all='skipping: needs BSLASHPSPEC (backslashes in pathspecs)'
 	test_done
 }
 
@@ -184,7 +184,7 @@ test_expect_success 'add wildcard f?z' '
 	)
 '
 
-test_expect_success 'add literal \? literal' '
+test_expect_success 'add literal \?' '
 	git init test-q-lit &&
 	(
 		cd test-q-lit &&
@@ -241,7 +241,7 @@ test_expect_success 'add literal hello\?world' '
 	)
 '
 
-test_expect_success 'add literal [abc]' '
+test_expect_success 'add literal \[abc\]' '
 	git init test-brackets-lit &&
 	(
 		cd test-brackets-lit &&
@@ -280,7 +280,7 @@ test_expect_success 'commit: wildcard *' '
 	)
 '
 
-test_expect_success 'commit: literal *' '
+test_expect_success 'commit: literal \*' '
 	git init test-c-asterisk-lit &&
 	(
 		cd test-c-asterisk-lit &&
@@ -328,7 +328,7 @@ test_expect_success 'commit: literal f\*' '
 	)
 '
 
-test_expect_success 'commit: wildcard pathspec limits commit' '
+test_expect_success 'commit: wildcard f**' '
 	git init test-c-pathlimit &&
 	(
 		cd test-c-pathlimit &&
diff --git a/usage.c b/usage.c
index 81913236a4a2ab..7545a616453449 100644
--- a/usage.c
+++ b/usage.c
@@ -7,6 +7,7 @@
 #include "git-compat-util.h"
 #include "gettext.h"
 #include "trace2.h"
+#include "strbuf.h"
 
 static void vfreportf(FILE *f, const char *prefix, const char *err, va_list params)
 {
@@ -375,14 +376,32 @@ void bug_fl(const char *file, int line, const char *fmt, ...)
 	va_end(ap);
 }
 
-NORETURN void you_still_use_that(const char *command_name)
+
+NORETURN void you_still_use_that(const char *command_name, const char *hint)
 {
+	struct strbuf percent_encoded = STRBUF_INIT;
+	strbuf_add_percentencode(&percent_encoded,
+				 command_name,
+				 STRBUF_ENCODE_SLASH);
+
+	fprintf(stderr,
+		_("'%s' is nominated for removal.\n"), command_name);
+
+	if (hint)
+		fputs(hint, stderr);
+
 	fprintf(stderr,
-		_("'%s' is nominated for removal.\n"
-		  "If you still use this command, please add an extra\n"
-		  "option, '--i-still-use-this', on the command line\n"
-		  "and let us know you still use it by sending an e-mail\n"
-		  "to <git@vger.kernel.org>.  Thanks.\n"),
-		command_name);
+		_("If you still use this command, here's what you can do:\n"
+		  "\n"
+		  "- read https://git-scm.com/docs/BreakingChanges.html\n"
+		  "- check if anyone has discussed this on the mailing\n"
+		  "  list and if they came up with something that can\n"
+		  "  help you: https://lore.kernel.org/git/?q=%s\n"
+		  "- send an email to <git@vger.kernel.org> to let us\n"
+		  "  know that you still use this command and were unable\n"
+		  "  to determine a suitable replacement\n"
+		  "\n"),
+		percent_encoded.buf);
+	strbuf_release(&percent_encoded);
 	die(_("refusing to run without --i-still-use-this"));
 }