[LLD][COFF] Clean paths in PDB even when /pdbsourcepath isn't used

[aganea]

Summary

Some of our build system scripts & third party solutions have a hard time without this.
Before this patch we had "dotted" paths such as:

StringTable:
        15:  - 'F:\blah\.\file.cpp'

[rnk]

lgtm

lld/COFF/PDB.cpp

283

Seems consistent

[amccarth]

I'm mildly surprised the make_absolute call doesn't remove unnecessary dotted paths. I guess that's related to the weird schism between sys::fs and sys::path.

Having recently tried out std::filesystem, I was pleasantly surprised that it was not nearly as terrible as I expected. :-) I know it doesn't meet the cross platform needs of LLVM, but maybe we should consider making LLVM's path handling more like it at some point...

[mstorsjo]

In D109030#2975835, @amccarth wrote:

Having recently tried out std::filesystem, I was pleasantly surprised that it was not nearly as terrible as I expected. :-) I know it doesn't meet the cross platform needs of LLVM, but maybe we should consider making LLVM's path handling more like it at some point...

I think(?) the LLVM path handling is kinda modelled to be like std::filesystem, although there are a number of more or less subtle differences. Adjusting it to be a closer match probably would be good, although it would require fixing up all cases of those subtle changes.

Regarding using std::filesystem in LLVM, I'm not offhand entirely sure which cross platform needs it doesn't support. On Windows it can handle paths with both kinds of slashes (and you can export it to either form), but it doesn't support handling paths with backslashes as separators on non-Windows platforms - which I guess can be needed in some cases.

Also regarding using std::filesystem in LLVM; libc++ does support std::filesystem on Windows these days, but it's problematic to use it in MSVC mode as it requires compiler-rt builtins for handling __int128, see https://reviews.llvm.org/D91139#2429595. So until that's resolved, it'd be hard to use it in LLVM itself as it would break self-hosting.

lld/COFF/PDB.cpp

if (sys::path::is_absolute(fileName, sys::path::Style::windows) ||
     return;
 
   // It's not absolute in any path syntax.  Relative paths necessarily refer to
   // the local file system, so we can make it native without ending up with a
   // nonsensical path.
   if (config->pdbSourcePath.empty()) {
     sys::path::native(fileName);
     sys::fs::make_absolute(fileName);
+    sys::path::remove_dots(fileName, true);
     return;
   }
 
   // Try to guess whether /PDBSOURCEPATH is a unix path or a windows path.
   // Since PDB's are more of a Windows thing, we make this conservative and only
   // decide that it's a unix path if we're fairly certain.  Specifically, if
   // it starts with a forward slash.
   SmallString<128> absoluteFileName = config->pdbSourcePath;
   sys::path::Style guessedStyle = absoluteFileName.startswith("/")
                                       ? sys::path::Style::posix
                                       : sys::path::Style::windows;
   sys::path::append(absoluteFileName, guessedStyle, fileName);
   sys::path::native(absoluteFileName, guessedStyle);
   sys::path::remove_dots(absoluteFileName, true, guessedStyle);
 
   fileName = std::move(absoluteFileName);
 }
 
 static void addTypeInfo(pdb::TpiStreamBuilder &tpiBuilder,
                         TypeCollection &typeTable) {
   // Start the TPI or IPI stream header.
   tpiBuilder.setVersionHeader(pdb::PdbTpiV80);

lld/test/COFF/pdb-relative-source-lines.test

 
 RUN: yaml2obj %S/Inputs/pdb_lines_1_relative.yaml -o %t/pdb_lines_1_relative.obj
 RUN: yaml2obj %S/Inputs/pdb_lines_2_relative.yaml -o %t/pdb_lines_2_relative.obj
 RUN: ./lld-link -debug "-pdbsourcepath:c:\src" -entry:main -nodefaultlib -out:out.exe -pdb:out.pdb pdb_lines_1_relative.obj pdb_lines_2_relative.obj
 RUN: llvm-pdbutil pdb2yaml -modules -module-files -module-syms -subsections=lines,fc %t/out.pdb | FileCheck %s
 RUN: ./lld-link -debug "-pdbsourcepath:/usr/src" -entry:main -nodefaultlib -out:out.exe -pdb:out.pdb pdb_lines_1_relative.obj pdb_lines_2_relative.obj
 RUN: llvm-pdbutil pdb2yaml -modules -module-files -module-syms -subsections=lines,fc %t/out.pdb | FileCheck --check-prefix=POSIX %s
 
+Also check without -pdbsourcepath
+RUN: ./lld-link -debug -entry:main -nodefaultlib -out:out.exe -pdb:out.pdb pdb_lines_1_relative.obj pdb_lines_2_relative.obj
+RUN: llvm-pdbutil pdb2yaml -modules -module-files -module-syms -subsections=lines,fc %t/out.pdb | FileCheck --check-prefix=ABSOLUTE %s
+
 CHECK-LABEL:  - Module:          'c:\src\pdb_lines_1_relative.obj'
 CHECK-NEXT:     ObjFile:         'c:\src\pdb_lines_1_relative.obj'
 CHECK:          SourceFiles:
 CHECK-NEXT:       - 'c:\src\pdb_lines_1.c'
 CHECK-NEXT:       - 'c:\src\foo.h'
 CHECK:          Subsections:
 CHECK:                - FileName:        'c:\src\pdb_lines_1.c'
 CHECK:                - FileName:        'c:\src\foo.h'

 POSIX-NEXT:         - cwd
 POSIX-NEXT:         - '/usr/src'
 POSIX-NEXT:         - exe
 POSIX-NEXT:         - '/usr/src/lld-link'
 POSIX-NEXT:         - pdb 
 POSIX-NEXT:         - '/usr/src/out.pdb'
 POSIX-NEXT:         - cmd
 POSIX-NEXT:         - '-debug -pdbsourcepath:/usr/src -entry:main -nodefaultlib -out:out.exe -pdb:out.pdb pdb_lines_1_relative.obj pdb_lines_2_relative.obj'
+
+ABSOLUTE-LABEL: StringTable:
+ABSOLUTE-NOT: {{/|\\}}.{{/|\\}}pdb_lines_1.c