Compile Servo with the latest version of rust stable (#30831)

This completes the transition to compiling Servo with rust stable. Some
nightly-only features are still used when compiling the `script` and
`crown` crates, as well as for some style unit tests. These will likely
break with newer compiler versions, but `crown` can be disabled for them
conditionally. This is just the first step.

This has some caveats:

1. We need to disable setting up the special linker on Linux. The -Z
   option isn't supported with stable rust so using this is out --
   meanwhile we can't be sure that lld is installed on most systems.
2. `cargo fmt` still uses some unstable options, so we need to rely on
   the unstable toolchain just for running `fmt`. The idea is to fix this
   gradually.

python/servo/command_base.py

@@ -524,12 +524,6 @@ class CommandBase(object):
         if self.config["build"]["rustflags"]:
             env['RUSTFLAGS'] += " " + self.config["build"]["rustflags"]
 
-        # Turn on rust's version of lld if we are on x86 Linux.
-        # TODO(mrobinson): Gradually turn this on for more platforms, when support stabilizes.
-        # See https://github.com/rust-lang/rust/issues/39915
-        if not self.cross_compile_target and effective_target == "x86_64-unknown-linux-gnu":
-            env['RUSTFLAGS'] += " " + servo.platform.get().linker_flag()
-
         if not (self.config["build"]["ccache"] == ""):
             env['CCACHE'] = self.config["build"]["ccache"]
 

python/servo/platform/base.py

@@ -66,9 +66,6 @@ class Base:
     def library_path_variable_name(self):
         raise NotImplementedError("Do not know how to set library path for platform.")
 
-    def linker_flag(self) -> str:
-        return ""
-
     def executable_suffix(self) -> str:
         return ""
 

python/servo/platform/linux.py

@@ -150,17 +150,6 @@ class Linux(Base):
         installed_something |= self._platform_bootstrap_gstreamer(force)
         return installed_something
 
-    def linker_flag(self) -> str:
-        # the rust-lld binary downloaded by rustup
-        # doesn't respect NIX_LDFLAGS and also needs
-        # other patches to work correctly. Use system
-        # version of lld for now. See
-        # https://github.com/NixOS/nixpkgs/issues/220717
-        if self.distro.lower() == 'nixos':
-            return '-C link-arg=-fuse-ld=lld'
-        else:
-            return '-Zgcc-ld=lld'
-
     def install_non_gstreamer_dependencies(self, force: bool) -> bool:
         install = False
         pkgs = []

python/servo/testing_commands.py

@@ -292,7 +292,10 @@ class MachCommands(CommandBase):
         else:
             manifest_dirty = wpt.manifestupdate.update(check_clean=True)
         tidy_failed = tidy.scan(not all_files, not no_progress, stylo=stylo, no_wpt=no_wpt)
-        rustfmt_failed = call(["cargo", "fmt", "--", "--check"])
+
+        call(["rustup", "install", "nightly-2023-03-18"])
+        call(["rustup", "component", "add", "rustfmt", "--toolchain", "nightly-2023-03-18"])
+        rustfmt_failed = call(["cargo", "+nightly-2023-03-18", "fmt", "--", "--check"])
 
         if rustfmt_failed:
             print("Run `./mach fmt` to fix the formatting")
@@ -396,7 +399,10 @@ class MachCommands(CommandBase):
         result = format_toml_files_with_taplo(check_only=False)
         if result != 0:
             return result
-        return call(["cargo", "fmt"])
+
+        call(["rustup", "install", "nightly-2023-03-18"])
+        call(["rustup", "component", "add", "rustfmt", "--toolchain", "nightly-2023-03-18"])
+        return call(["cargo", "+nightly-2023-03-18", "fmt"])
 
     @Command('update-wpt',
              description='Update the web platform tests',