Render file patches with a decorated Editor

[smashwilson]

Use decorations within an Atom TextEditor element to implement a file patch item. This should get us improved performance for large diffs, editable diff support, and open the path for multi-file diff views like a commit or pull request pane.

Just to set proper expectations, I'll likely need to pause and resume this a few times before it lands. Don't worry, I won't forget about it 😄

Remaining Work

• Split FilePatchController out into a FilePatchItem, FilePatchContainer, FilePatchController, and FilePatchView, as per Improve React component organization #1436.
• Inherit basic item wiring (getTitle(), etc) onto FilePatchItem.
• Render an <AtomTextEditor> within the FilePatchView.
• Model: render a FilePatch to the unadorned text that should be displayed within the editor accompanied by the buffer line ranges that correspond to each hunk and line range
• View: render each group of controls from the original FilePatchView within an appropriately placed Decoration
  • CSS tweaks to keep it looking right
• Controller: port interactions over and wire 'em up to the right controls
  • Figure out how to preserve selection semantics
• Update Marker and Decoration components to handle prop changes correctly
• Correctly and efficiently update FilePatchView decorations when the FilePatch changes due to staging operations
• Upstream in Atom Multiple, custom line number gutters atom#17736
  • Support custom line numberings in the line number gutter
  • Support the creation of multiple line number gutters
  • Investigate and correct the weird doubled line number labels in custom line-number gutters
  • Write tests for the new gutter code in TextEditorElement's tests
• Fix StagingView selection sync regression
• "No changes to display" should be centered in the pane
• Rework PresentedFilePatch model to unify it with the old model and prevent us from keeping two copies of the diff around
  • Store all patch text in a single String owned by Patch
  • Use an IndexedRowRange to unify an Atom Range with a pair of string offsets
  • Eliminate HunkLine and replace it with IndexedRowRanges within each Hunk that delimit addition and deletion regions
  • Rework partial and complete stage and unstage patch generation
  • Use null objects for missing Files or Patches
  • Unify new model objects within a FilePatch
  • Use a nullFilePatch to signal a missing patch
  • Efficiently determine the Hunk owning a given buffer row
  • Generate old and new line numbers given a buffer row within the patch
  • Use buffer rows to represent lines within a FilePatchSelection
• Adjust the FilePatchView to use the new model instead of a PresentedFilePatch
• An empty FilePatch should have navigation controls
• Restore commands and hotkeys
• Synchronize the FilePatchSelection and the TextEditor selections
  • Derive the selected patch rows from the current TextEditor selection ranges
  • Handle ctrl- and cmd-clicks and drags on the gutters by adjusting the TextEditor selections
  • Fix patch application
  • Heuristically preserve selection rows when a new FilePatch is generated
  • Suppress setState while the AtomTextEditor is being re-rendered with new content
  • Delete the now-unused FilePatchSelection and its tests
• Stretch hunk and change region ranges to the end of the last line
• Catch test coverage up to the speculative work. Get us ✅ again.
• Store the patch text in a TextBuffer in the Patch model instead of a String
  • Allow an AtomTextEditor to be initialized with an externally owned TextBuffer.
  • Store markers within Regions and Hunks instead of IndexedRowRanges.
  • Organize the markers within a given patch into layers.
  • Create markers instead of IndexedRowRanges in buildFilePatch().
  • Roll a new FilePatch into a previous FilePatch's buffer.
  • Move getHunkAt() into Patch and FilePatch.
  • Allow Markers and MarkerLayers to inherit externally managed resources by ID
  • Decorate Patch-owned MarkerLayers and Markers in FilePatchView.
  • Preserve the buffer when a new FilePatch arrives.
  • Make the CommitView use an external text buffer for the commit message.
• Re-introduce hunk selections
• Create a prerelease tag on this branch so that we can dogfood this

v0.19.1-0

• Fix discarding hunks and lines
• Stage, unstage, or discard patches with a blank line
• Correct exception when staging or unstaging the final hunk

v0.19.1-1

• Correct breakage when decorating destroyed markers
• Re-introduce the "toggle hunk" keybinding
• Be less sensitive to stale MarkerLayers when rendering
• Re-introduce hunk-mode navigation controls
• Selection decorations only appear on the first row when a row is soft-wrapped
• "TypeError: Cannot read property 'getMarker' of undefined"
• Re-render on first click with soft-wrapped lines. Upstream fix: Update soft wrap margins on gutter re-measurement atom#18087
• Reword "(un)stage selections" buttons to mention lines

v0.19.1-2

• Include a final empty row in the selected row set
• TypeError: Cannot destructure property holder of 'undefined' or 'null' when conflicts are encountered
• Empty diff view when staging and unstaging changes
• Include keyboard shortcuts in (un)stage selection buttons

v0.19.1-3

• "Discard changes" regressed again
• Begin in hunk selection mode
• ✅ Green tests again checkpoint ✅

v0.19.1-5

• Reintroduce + and - indicators in a gutter
• Improve the context menu on diffs
• Correct keyboard focus when opening FilePatchItem
• Track down stalling and failing tests on CircleCI
• Reintroduce "surfacing" focus to the Git tab with cmd/ctrl-right

v0.19.1-6

• Register more missing commands
• Port Handle staged changes with special characters in the filename #1667 on top of the rewrite

v0.22.1-0

• Integration tests for patch correctness

Concurrent with review

• Ensure CI runs a full stable, beta, and dev matrix on all three platforms - Fill out the build matrix #1663
• Handle CI tests that run against versions of Atom older than the version specified in package.json - Skip all tests when engines.atom has been bumped to exclude the current Atom version #1664
• 🎨 ✨ @simurai design magic CSS pass 🎨 ✨

Checks

• Ensure that the pane item works well
  • ... as a pending pane item
  • ... on serialize and deserialize
  • ... when changing between multiple repositories
• Ensure that our keyboard shortcuts and commands all still work properly
• Ensure that we don't regress our ability to handle rapid staging and unstaging
• Make sure I delete the .old.js files 😬
• Regression check: Should not display mode change for added file that is executable #1312
• Regression check: Uncaught (in promise) TypeError: Cannot read property 'getLines' of undefined #1241

Stretch goals

• Make the editor editable. Alter the FilePatch accordingly. Filed as Editable diffs in FilePatchItems #1720.
• Add syntax highlighting by setting the editor's grammar.
• Support folding of the diff
• Efficiently match up the rendered decorations by deriving a durable hunk-specific key.
• Keep hunk headers visible as you scroll: Always keep hunk-view header visible #1642

Resources

A Guided Tour to that Giant "Files changed" Tab

Fixes #1502. ...Eventually 🕐

[maxbrunsfeld]

[simurai]

I shall remember this PR as "The wall of checkboxes PR". 😂