rust: Override the default MSVCRT when linking Rust and !rust together

Rust by default links with the default MSVCRT, (dynamic, release).
MSVCRT's cannot be mixed, so if Meson compiles a C or C++ library and
links it with the debug MSVCRT, then tries to link that with the Rust
library there will be failures. There is no built-in way to fix this for
rustc, so as a workaround we inject the correct arguments early in the
linker line (before any libs at least) to change the runtime. This seems
to work and is recommended as workaround in the upstream rust bug
report: rust-lang/rust#39016.

Given that this bug report has been opened since 2017, it seems unlikely
to be fixed anytime soon, and affects all (currently) released versions
of Rust.

mesonbuild/backend/ninjabackend.py

@@ -1943,6 +1943,49 @@ def generate_rust_target(self, target: build.BuildTarget) -> None:
         args += output
         linkdirs = mesonlib.OrderedSet()
         external_deps = target.external_deps.copy()
+
+        # Have we already injected msvc-crt args?
+        #
+        # If we don't have A C, C++, or Fortran compiler that is
+        # VisualStudioLike treat this as if we've already injected them
+        #
+        # We handle this here rather than in the rust compiler because in
+        # general we don't want to link rust targets to a non-default crt.
+        # However, because of the way that MSCRTs work you can only link to one
+        # per target, so if A links to the debug one, and B links to the normal
+        # one you can't link A and B. Rust is hardcoded to the default one,
+        # so if we compile C/C++ code and link against a non-default MSCRT then
+        # linking will fail. We can work around this by injecting MSCRT link
+        # arguments early in the rustc command line
+        # https://github.com/rust-lang/rust/issues/39016
+        crt_args_injected = not any(x is not None and x.get_argument_syntax() == 'msvc' for x in
+                                    (self.environment.coredata.compilers[target.for_machine].get(l)
+                                     for l in ['c', 'cpp', 'fortran']))
+
+        crt_link_args: T.List[str] = []
+        try:
+            buildtype = self.environment.coredata.options[OptionKey('buildtype')].value
+            crt = self.environment.coredata.options[OptionKey('b_vscrt')].value
+            is_debug = buildtype == 'debug'
+
+            if crt == 'from_buildtype':
+                crt = 'mdd' if is_debug else 'md'
+            elif crt == 'static_from_buildtype':
+                crt = 'mtd' if is_debug else 'mt'
+
+            if crt == 'mdd':
+                crt_link_args = ['-l', 'static=msvcrtd']
+            elif crt == 'md':
+                # this is the default, no need to inject anything
+                crt_args_injected = True
+            elif crt == 'mtd':
+                crt_link_args = ['-l', 'static=libcmtd']
+            elif crt == 'mt':
+                crt_link_args = ['-l', 'static=libcmt']
+
+        except KeyError:
+            crt_args_injected = True
+
         # TODO: we likely need to use verbatim to handle name_prefix and name_suffix
         for d in target.link_targets:
             linkdirs.add(d.subdir)
@@ -1956,7 +1999,13 @@ def generate_rust_target(self, target: build.BuildTarget) -> None:
                 d_name = self._get_rust_dependency_name(target, d)
                 args += ['--extern', '{}={}'.format(d_name, os.path.join(d.subdir, d.filename))]
                 project_deps.append(RustDep(d_name, self.rust_crates[d.name].order))
-            elif isinstance(d, build.StaticLibrary):
+                continue
+
+            if not crt_args_injected and not {'c', 'cpp', 'fortran'}.isdisjoint(d.compilers):
+                args += crt_link_args
+                crt_args_injected = True
+
+            if isinstance(d, build.StaticLibrary):
                 # Rustc doesn't follow Meson's convention that static libraries
                 # are called .a, and import libraries are .lib, so we have to
                 # manually handle that.
@@ -1996,6 +2045,10 @@ def generate_rust_target(self, target: build.BuildTarget) -> None:
                 args += ['--extern', '{}={}'.format(d_name, os.path.join(d.subdir, d.filename))]
                 project_deps.append(RustDep(d_name, self.rust_crates[d.name].order))
             else:
+                if not crt_args_injected and not {'c', 'cpp', 'fortran'}.isdisjoint(d.compilers):
+                    crt_args_injected = True
+                    crt_args_injected = True
+
                 if rustc.linker.id in {'link', 'lld-link'}:
                     if verbatim:
                         # If we can use the verbatim modifier, then everything is great

test cases/rust/20 rust and cpp/test.json

@@ -0,0 +1,15 @@
+{
+  "matrix": {
+    "options": {
+      "b_vscrt": [
+        { "val": "none" },
+        { "val": "mdd" },
+        { "val": "md" },
+        { "val": "mtd" },
+        { "val": "mt" },
+        { "val": "from_buildtype" },
+        { "val": "static_from_buildtype" }
+      ]
+    }
+  }
+}