Commits on Sep 8, 2021

1. submodule: lazily add submodule ODBs as alternates …

   Teach Git to add submodule ODBs as alternates to the object store of
   the_repository only upon the first access of an object not in
   the_repository, and not when add_submodule_odb() is called.
   
   This provides a means of gradually migrating from accessing a
   submodule's object through alternates to accessing a submodule's object
   by explicitly passing its repository object. Any Git command can declare
   that it might access submodule objects by calling add_submodule_odb()
   (as they do now), but the submodule ODBs themselves will not be added
   until needed, so individual commands and/or combinations of arguments
   can be migrated one by one.
   
   [The advantage of explicit repository-object passing is code clarity (it
   is clear which repository an object read is from), performance (there is
   no need to linearly search through all submodule ODBs whenever an object
   is accessed from any repository, whether superproject or submodule), and
   the possibility of future features like partial clone submodules (which
   right now is not possible because if an object is missing, we do not
   know which repository to lazy-fetch into).]
   
   This commit also introduces an environment variable that a test may set
   to make the actual registration of alternates fatal, in order to
   demonstrate that its codepaths do not need this registration.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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2. grep: use submodule-ODB-as-alternate lazy-addition …

   In the parent commit, Git was taught to add submodule ODBs as alternates
   lazily, but grep does not use this because it computes the path to add
   directly, not going through add_submodule_odb(). Add an equivalent to
   add_submodule_odb() that takes the exact ODB path and teach grep to use
   it.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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3. grep: typesafe versions of grep_source_init …

   grep_source_init() can create "struct grep_source" objects and,
   depending on the value of the type passed, some void-pointer parameters have
   different meanings. Because one of these types (GREP_SOURCE_OID) will
   require an additional parameter in a subsequent patch, take the
   opportunity to increase clarity and type safety by replacing this
   function with individual functions for each type.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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4. grep: read submodule entry with explicit repo …

   Replace an existing parse_object_or_die() call (which implicitly works
   on the_repository) with a function call that allows a repository to be
   passed in. There is no such direct equivalent to parse_object_or_die(),
   but we only need the type of the object, so replace with
   oid_object_info().
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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5. grep: allocate subrepos on heap …

   Currently, struct repository objects corresponding to submodules are
   allocated on the stack in grep_submodule(). This currently works because
   they will not be used once grep_submodule() exits, but a subsequent
   patch will require these structs to be accessible for longer (perhaps
   even in another thread). Allocate them on the heap and clear them only
   at the very end.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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6. grep: add repository to OID grep sources …

   Record the repository whenever an OID grep source is created, and teach
   the worker threads to explicitly provide the repository when accessing
   objects.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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7. submodule-config: pass repo upon blob config read …

   When reading the config of a submodule, if reading from a blob, read
   using an explicitly specified repository instead of by adding the
   submodule's ODB as an alternate and then reading an object from
   the_repository.
   
   This makes the "grep --recurse-submodules with submodules without
   .gitmodules in the working tree" test in t7814 work when
   GIT_TEST_FATAL_REGISTER_SUBMODULE_ODB is true.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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8. t7814: show lack of alternate ODB-adding …

   The previous patches have made "git grep" no longer need to add
   submodule ODBs as alternates, at least for the code paths tested in
   t7814. Demonstrate this by making adding a submodule ODB as an alternate
   fatal in this test.
   
   Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
   Reviewed-by: Emily Shaffer <emilyshaffer@google.com>
   Reviewed-by: Matheus Tavares <matheus.bernardino@usp.br>
   Signed-off-by: Junio C Hamano <gitster@pobox.com>

   

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