rust: Rebuild targets when compiler got updated

mesonbuild/backend/ninjabackend.py

@@ -1877,7 +1877,7 @@ def generate_rust_target(self, target: build.BuildTarget) -> None:
         self.generate_generator_list_rules(target)
 
         # dependencies need to cause a relink, they're not just for ordering
-        deps: T.List[str] = []
+        deps: T.List[str] = [rustc.get_exe_file()]
 
         # Dependencies for rust-project.json
         project_deps: T.List[RustDep] = []

mesonbuild/compilers/compilers.py

@@ -631,6 +631,9 @@ def get_exelist(self, ccache: bool = True) -> T.List[str]:
     def get_linker_exelist(self) -> T.List[str]:
         return self.linker.get_exelist() if self.linker else self.get_exelist()
 
+    def get_exe_file(self) -> str:
+        return os.path.realpath(self.exelist_no_ccache[0])
+
     @abc.abstractmethod
     def get_output_args(self, outputname: str) -> T.List[str]:
         pass

mesonbuild/compilers/rust.py

@@ -18,6 +18,8 @@
 import re
 import typing as T
 
+from functools import lru_cache
+
 from .. import coredata
 from ..mesonlib import EnvironmentException, MesonException, Popen_safe_logged, OptionKey
 from .compilers import Compiler, rust_buildtype_args, clike_debug_args
@@ -79,6 +81,19 @@ def __init__(self, exelist: T.List[str], version: str, for_machine: MachineChoic
         if 'link' in self.linker.id:
             self.base_options.add(OptionKey('b_vscrt'))
         self.native_static_libs: T.List[str] = []
+        # Resolve the real rustc executable. When using rustup, "rustc" in PATH
+        # is a wrapper that won't change when updating the toolchain, which
+        # means ninja would not rebuild rust targets after "rustup update". That
+        # can cause build issues because different rustc versions are generally
+        # uncompatible. This also means that once a Meson project has been
+        # configured, changing the default toolchain with e.g.
+        # "rustup default nightly" won't have any effect.
+        sysroot = self.get_sysroot()
+        real_rustc = os.path.join(sysroot, 'bin', 'rustc')
+        if os.path.exists(real_rustc):
+            exelist = [real_rustc] + exelist[1:]
+            self.exelist = exelist
+            self.exelist_no_ccache = exelist
 
     def needs_static_linker(self) -> bool:
         return False
@@ -126,6 +141,7 @@ def get_dependency_gen_args(self, outtarget: str, outfile: str) -> T.List[str]:
     def get_buildtype_args(self, buildtype: str) -> T.List[str]:
         return rust_buildtype_args[buildtype]
 
+    @lru_cache(maxsize=None)
     def get_sysroot(self) -> str:
         cmd = self.get_exelist(ccache=False) + ['--print', 'sysroot']
         p, stdo, stde = Popen_safe_logged(cmd)

mesonbuild/interpreter/interpreter.py

@@ -1519,6 +1519,7 @@ def add_languages_for(self, args: T.List[str], required: bool, for_machine: Mach
                     comp = compilers.detect_compiler_for(self.environment, lang, for_machine, skip_sanity_check)
                     if comp is None:
                         raise InvalidArguments(f'Tried to use unknown language "{lang}".')
+                    self.add_build_def_file(comp.get_exe_file())
                 except mesonlib.MesonException:
                     if not required:
                         mlog.log('Compiler for language',