dependencies: Convert /c/foo/bar paths to C:/foo/bar

MSVC cannot handle MinGW-esque /c/foo paths, convert them to C:/foo.
We cannot resolve other paths starting with / like /home/foo so leave
them as-is so the user gets an error/warning from the compiler/linker.

These paths are commonly found in pkg-config files generated using
Autotools inside MinGW/MSYS and MinGW/MSYS2 environments.

Currently this is only done for PkgConfigDependency.

mesonbuild/dependencies/base.py

@@ -22,6 +22,7 @@ import shlex
 import shutil
 import textwrap
 from enum import Enum
+from pathlib import PurePath
 
 from .. import mlog
 from .. import mesonlib
@@ -424,6 +425,20 @@ class PkgConfigDependency(ExternalDependency):
         self.link_args = []
         libpaths = []
         for lib in shlex.split(out):
+            # MSVC cannot handle MinGW-esque /c/foo paths, convert them to C:/foo.
+            # We cannot resolve other paths starting with / like /home/foo so leave
+            # them as-is so the user gets an error/warning from the compiler/linker.
+            if self.compiler.id == 'msvc':
+                # Library search path
+                if lib.startswith('-L/'):
+                    pargs = PurePath(lib[2:]).parts
+                    if len(pargs) > 1 and len(pargs[1]) == 1:
+                        lib = '-L{}:/{}'.format(pargs[1], '/'.join(pargs[2:]))
+                # Full path to library or .la file
+                elif lib.startswith('/'):
+                    pargs = PurePath(lib).parts
+                    if len(pargs) > 1 and len(pargs[1]) == 1:
+                        lib = '{}:/{}'.format(pargs[1], '/'.join(pargs[2:]))
             # If we want to use only static libraries, we have to look for the
             # file ourselves instead of depending on the compiler to find it
             # with -lfoo or foo.lib. However, we can only do this if we already

test cases/unit/17 pkgconfig static/meson.build

@@ -5,8 +5,22 @@ if build_machine.system() != 'windows'
 else
   # pkg-config files should not use paths with \
   prefix_parts = meson.source_root().split('\\')
-  prefix = '/'.join(prefix_parts)
+  # If the path is C:/foo/bar, convert it to /c/foo/bar so we can test if our
+  # automatic conversion to C:/foo/bar inside PkgConfigDependency is working.
+  if prefix_parts[0][1] == ':'
+    drive = prefix_parts[0][0]
+  else
+    drive = prefix_parts[0]
+  endif
+  new_parts = []
+  foreach part : prefix_parts
+    if part != prefix_parts[0]
+      new_parts += part
+    endif
+  endforeach
+  prefix = '/@0@/@1@'.format(drive, '/'.join(new_parts))
 endif
+message(prefix)
 
 # Escape spaces
 prefix_parts = prefix.split(' ')