backends: Use POSIX paths for target paths

This commit completes 5de09cbe8838e8febf1ca3aa83b53cf06972bff3,
ensuring that only POSIX style paths are passed to the compiler
line, and thus fixing UNIX-style tools that treat single
backward slashes as Unicode escaped characters.

Fixes #12191

Completes #12534

Completes #12564

3 files changed, 13 insertions, 12 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index ed57a4c1b..3aab420e8 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -150,7 +150,7 @@ class TargetInstallData:
     def __post_init__(self, outdir_name: T.Optional[str]) -> None:
         if outdir_name is None:
             outdir_name = os.path.join('{prefix}', self.outdir)
-        self.out_name = os.path.join(outdir_name, os.path.basename(self.fname))
+        self.out_name = Path(outdir_name, os.path.basename(self.fname)).as_posix()
 
 @dataclass(eq=False)
 class InstallEmptyDir:
@@ -307,16 +307,16 @@ class Backend:
         else:
             assert isinstance(t, build.BuildTarget), t
             filename = t.get_filename()
-        return os.path.join(self.get_target_dir(t), filename)
+        return Path(self.get_target_dir(t), filename).as_posix()
 
     def get_target_filename_abs(self, target: T.Union[build.Target, build.CustomTargetIndex]) -> str:
-        return os.path.join(self.environment.get_build_dir(), self.get_target_filename(target))
+        return Path(self.environment.get_build_dir(), self.get_target_filename(target)).as_posix()
 
     def get_target_debug_filename(self, target: build.BuildTarget) -> T.Optional[str]:
         assert isinstance(target, build.BuildTarget), target
         if target.get_debug_filename():
             debug_filename = target.get_debug_filename()
-            return os.path.join(self.get_target_dir(target), debug_filename)
+            return Path(self.get_target_dir(target), debug_filename).as_posix()
         else:
             return None
 
@@ -324,7 +324,7 @@ class Backend:
         assert isinstance(target, build.BuildTarget), target
         if not target.get_debug_filename():
             return None
-        return os.path.join(self.environment.get_build_dir(), self.get_target_debug_filename(target))
+        return Path(self.environment.get_build_dir(), self.get_target_debug_filename(target)).as_posix()
 
     def get_source_dir_include_args(self, target: build.BuildTarget, compiler: 'Compiler', *, absolute_path: bool = False) -> T.List[str]:
         curdir = target.get_subdir()
diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index 73f2db7c4..10f77e7cc 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -3353,7 +3353,7 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
     def get_target_shsym_filename(self, target):
         # Always name the .symbols file after the primary build output because it always exists
         targetdir = self.get_target_private_dir(target)
-        return os.path.join(targetdir, target.get_filename() + '.symbols')
+        return Path(targetdir, target.get_filename() + '.symbols').as_posix()
 
     def generate_shsym(self, target) -> None:
         target_file = self.get_target_filename(target)
@@ -3372,7 +3372,7 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
         self.add_build(elem)
 
     def get_import_filename(self, target) -> str:
-        return os.path.join(self.get_target_dir(target), target.import_filename)
+        return Path(self.get_target_dir(target), target.import_filename).as_posix()
 
     def get_target_type_link_args(self, target, linker):
         commands = []
diff --git a/mesonbuild/mintro.py b/mesonbuild/mintro.py
index 6986186bd..57fa286b7 100644
--- a/mesonbuild/mintro.py
+++ b/mesonbuild/mintro.py
@@ -128,7 +128,7 @@ def list_installed(installdata: backends.InstallData) -> T.Dict[str, str]:
 def list_install_plan(installdata: backends.InstallData) -> T.Dict[str, T.Dict[str, T.Dict[str, T.Optional[str]]]]:
     plan: T.Dict[str, T.Dict[str, T.Dict[str, T.Optional[str]]]] = {
         'targets': {
-            os.path.join(installdata.build_dir, target.fname): {
+            Path(installdata.build_dir, target.fname).as_posix(): {
                 'destination': target.out_name,
                 'tag': target.tag or None,
                 'subproject': target.subproject or None,
@@ -145,13 +145,14 @@ def list_install_plan(installdata: backends.InstallData) -> T.Dict[str, T.Dict[s
     }.items():
         # Mypy doesn't recognize SubdirInstallData as a subclass of InstallDataBase
         for data in data_list: # type: ignore[attr-defined]
+            data_path = Path(data.path).as_posix()
             data_type = data.data_type or key
-            install_path_name = data.install_path_name
+            install_path_name = Path(data.install_path_name)
             if key == 'headers':  # in the headers, install_path_name is the directory
-                install_path_name = os.path.join(install_path_name, os.path.basename(data.path))
+                install_path_name = install_path_name / os.path.basename(data.path)
 
             entry = {
-                'destination': install_path_name,
+                'destination': install_path_name.as_posix(),
                 'tag': data.tag or None,
                 'subproject': data.subproject or None,
             }
@@ -162,7 +163,7 @@ def list_install_plan(installdata: backends.InstallData) -> T.Dict[str, T.Dict[s
                 entry['exclude_files'] = list(exclude_files)
 
             plan[data_type] = plan.get(data_type, {})
-            plan[data_type][data.path] = entry
+            plan[data_type][data_path] = entry
 
     return plan