[llvm] [lit] Fix builtin diff importing system lit.util in subprocess mode (PR #206723)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-testing-tools

Author: Prasoon Kumar (prasoon054)

<details>
<summary>Changes</summary>

'import lit.util' silently picks up a system-installed lit package instead of the local one, which may lack abs_path_preserve_drive.

Switch to 'from .. import util': in subprocess mode __package__ is None, so the relative import raises ImportError and the fallback correctly picks up the local util.py via PYTHONPATH

---
Full diff: https://github.com/llvm/llvm-project/pull/206723.diff


1 Files Affected:

- (modified) llvm/utils/lit/lit/builtin_commands/diff.py (+9-10) 


``````````diff
diff --git a/llvm/utils/lit/lit/builtin_commands/diff.py b/llvm/utils/lit/lit/builtin_commands/diff.py
index 579a2649bc0af..9d1a398106664 100644
--- a/llvm/utils/lit/lit/builtin_commands/diff.py
+++ b/llvm/utils/lit/lit/builtin_commands/diff.py
@@ -7,18 +7,17 @@
 import sys
 
 # diff.py runs in two modes during the in-process migration:
-#   - In-process (default): imported as 'lit.builtin_commands.diff', so the
-#     'lit' package is already resolvable => lit.util works
-#   - Spawned fallback: run standalone via 'sys.executable diff.py', with
-#     PYTHONPATH set to the 'lit/' directory itself, not its parent. No entry
-#     on sys.path is the parent of 'lit/', so 'lit' can't be imported as package =>
-#     'lit.util' raises ImportError. util.py sits directly in that PYTHONPATH
-#     dir, so bare 'import util' resolves instead.
-# Both paths load the same module; the fallback handles the path difference.
-# TODO: Collapse to a standard 'import lit.util' once standalone spawning is removed.
+#   - In-process: imported as 'lit.builtin_commands.diff', so __package__ is
+#     set and the relative import resolves to lit.util from the source tree.
+#   - Spawned fallback: run as __main__ with __package__=None, so the relative
+#     import raises ImportError and the fallback picks up util.py via PYTHONPATH
+#     pointing at the lit/ directory.
+# A relative import is used (not 'import lit.util') to avoid accidentally
+# importing a system-installed lit package that may lack abs_path_preserve_drive.
+# TODO: Collapse to 'from .. import util' once standalone spawning is removed.
 
 try:
-    import lit.util as util
+    from .. import util
 except ImportError:
     import util
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/206723