Fix: Reverse git diff direction to correctly detect renamed files with -M95

[chandprashant92]

Bug: git diff HEAD..merge-base silently misses all affected modules

when a PR contains only pure file renames

Problem

GitChangedFilesSource constructs the changed-files command as:

git --no-pager diff --name-only -M95 $top..$sha

Where top = "HEAD" (the PR tip) and sha = the merge-base commit.
This produces:

git diff --name-only -M95 HEAD..merge-base

The direction is reversed. The semantically correct command for
"what changed in this PR?" is merge-base..HEAD.

Why this is silent for normal PRs (and why it was never caught)

For content-modified files, git diff A..B and git diff B..A report
the same filenames — direction doesn't affect --name-only output.

The bug only surfaces when a PR consists entirely of pure renames
(files moved via git mv with 100% content similarity). In that case,
-M95 rename detection kicks in and --name-only outputs the
destination path relative to the diff direction:

Command	--name-only output
git diff merge-base..HEAD	NEW paths (correct for AMD's ProjectGraph)
git diff HEAD..merge-base	OLD paths (wrong — these don't exist in the current ProjectGraph)

With the reversed direction, AMD receives a list of file paths that no
longer exist in the project tree → changedProjects = 0, unknownFiles
accumulates all renamed files → the buildAllWhenNoProjectsChanged
safety net is not triggered (because unknownFiles is non-empty) →
AMD reports 0 affected modules and silently skips all tasks.

Reproduction

git mv src/foo/Bar.kt src/baz/Bar.kt
git commit -m "rename"

# AMD (broken) — shows OLD path → no module match
git diff --name-only -M95 HEAD..$(git merge-base HEAD origin/main)
# Output: src/foo/Bar.kt  ← old path, doesn't exist in current ProjectGraph

# Correct — shows NEW path → module matched
git diff --name-only -M95 $(git merge-base HEAD origin/main)..HEAD
# Output: src/baz/Bar.kt  ← new path, correctly resolved to module

Fix

Swap the argument order in GitChangedFilesSource:

// Before
"$CHANGED_FILES_CMD_PREFIX $top..$sha"

// After
"$CHANGED_FILES_CMD_PREFIX $sha..$top"

No behaviour change for content-modified files. Correctly handles
pure-rename PRs by reporting new destination paths that map to the
current project graph.

[CLAassistant]

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[chandprashant92]

Hi @joshafeinberg, would you mind reviewing my changes, please?