Non hashable args like fdebug-prefix-map & related

[borjamunozf]

Hello!

I realized that compilers arguments/flags for gcc like the mentioned above are being used in the hash_key function. This means that strategies for handling the absolute paths to relatives regarding debug info or in similar fashion that involves passing a dynamic value into the argument depending of the builder origin will create a different hash key.

From my point of view, these kind of arguments should not affect the computer hash key at all:

• -_fdebug-prefix-map=${PWD}=.
• -fmacro-prefix-map
• ffile-prefix-map
• fdebug-compilation-dir

A naive change could just include a non-hashable list of args that should be skipped or not considered into the hash key.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.60%. Comparing base (9fd99c7) to head (ad5d821).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2409      +/-   ##
==========================================
+ Coverage   71.58%   71.60%   +0.01%     
==========================================
  Files          65       65              
  Lines       36372    36398      +26     
==========================================
+ Hits        26037    26061      +24     
- Misses      10335    10337       +2     

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[necto]

• -fmacro-prefix-map
• ffile-prefix-map

Note that these arguments do affect preprocessor output, so they should still be passed to the preprocessor. Using Clang compiler, I had success with the following patch:

modified   src/compiler/clang.rs
@@ -220,6 +220,7 @@ counted_array!(pub static ARGS: [ArgInfo<gcc::ArgData>; _] = [
     flag!("-fcxx-modules", TooHardFlag),
     take_arg!("-fdebug-compilation-dir", OsString, Separated, PassThrough),
     take_arg!("-fembed-offload-object", PathBuf, Concatenated(b'='), ExtraHashFile),
+    take_arg!("-ffile-prefix-map", OsString, Concatenated(b'='), PreprocessorArgument),
     flag!("-fmodules", TooHardFlag),
     flag!("-fno-color-diagnostics", NoDiagnosticsColorFlag),
     flag!("-fno-pch-timestamp", PassThroughFlag),