fix rustc -l argument on Windows

On Windows, rustc searches both FOO.lib and libFOO.lib when passed -lfoo.
This means that the check for nonstandard names is too struct, and indeed
it breaks passing for example -lkernel32 (which adds kernel32.lib to the
link).

Fix this by special casing Windows.  Extract the logic to the Rust
compiler class for clarity.

Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

mesonbuild/backend/ninjabackend.py

@@ -2050,14 +2050,8 @@ def _link_library(libname: str, static: bool, bundle: bool = False) -> None:
             if rustc.has_verbatim():
                 modifiers.append('+verbatim')
             else:
-                # undo the effects of -l without verbatim
-                badname = not is_library(libname)
-                libname, ext = os.path.splitext(libname)
-                if libname.startswith('lib'):
-                    libname = libname[3:]
-                else:
-                    badname = True
-                if badname:
+                libname = rustc.lib_file_to_l_arg(self.environment, libname)
+                if libname is None:
                     raise MesonException(f"rustc does not implement '-l{type_}:+verbatim'; cannot link to '{orig_libname}' due to nonstandard name")
 
             if modifiers:

mesonbuild/compilers/rust.py

@@ -13,7 +13,7 @@
 from .. import options
 from ..mesonlib import EnvironmentException, MesonException, Popen_safe_logged, version_compare
 from ..options import OptionKey
-from .compilers import Compiler, CompileCheckMode, clike_debug_args
+from .compilers import Compiler, CompileCheckMode, clike_debug_args, is_library
 
 if T.TYPE_CHECKING:
     from ..options import MutableKeyedOptionDictType
@@ -208,6 +208,31 @@ def has_verbatim(self) -> bool:
         # being linked.  However, Meson uses "bundle", not "whole_archive".
         return False
 
+    def lib_file_to_l_arg(self, env: Environment, libname: str) -> T.Optional[str]:
+        """Undo the effects of -l on the filename, returning the
+           argument that can be passed to -l, or None if the
+           library name is not supported."""
+        if not is_library(libname):
+            return None
+        libname, ext = os.path.splitext(libname)
+
+        # On Windows, -lfoo searches either foo.lib or libfoo.a.
+        # Elsewhere, it only searches both static and shared libraries with
+        # the "lib" prefix; for simplicity just skip .lib which is never used.
+        if env.machines[self.for_machine].is_windows():
+            if ext == 'lib':
+                return libname
+            if ext != 'a':
+                return None
+        else:
+            if ext == 'lib':
+                return None
+
+        if not libname.startswith('lib'):
+            return None
+        libname = libname[3:]
+        return libname
+
     def get_debug_args(self, is_debug: bool) -> T.List[str]:
         return clike_debug_args[is_debug]