Simplify rustc_args.py, and align its code with what Meson's own Cargo.toml
translator does in v1.10.

Bump unknown_lints to "forbid", so that it will certainly override Cargo.toml's
"allow" level.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 meson.build                |  7 +++----
 scripts/rust/rustc_args.py | 20 ++------------------
 2 files changed, 5 insertions(+), 22 deletions(-)

diff --git a/meson.build b/meson.build
index 270181038bf..e6a11cefdb7 100644
--- a/meson.build
+++ b/meson.build
@@ -128,14 +128,13 @@ if have_rust
   rustc_args = [find_program('scripts/rust/rustc_args.py'),
     '--rustc-version', rustc.version(),
     '--workspace', meson.project_source_root() / 'rust']
-  if get_option('strict_rust_lints')
-    rustc_args += ['--strict-lints']
-  endif
-
   rustfmt = find_program('rustfmt', required: false)
 
   rustc_lint_args = run_command(rustc_args, '--lints',
      capture: true, check: true).stdout().strip().splitlines()
+  if get_option('strict_rust_lints')
+    rustc_lint_args += ['-Dwarnings', '-Funknown_lints']
+  endif
 
   # Apart from procedural macros, our Rust executables will often link
   # with C code, so include all the libraries that C code needs.  This
diff --git a/scripts/rust/rustc_args.py b/scripts/rust/rustc_args.py
index 63b0748e0d3..8fb77785350 100644
--- a/scripts/rust/rustc_args.py
+++ b/scripts/rust/rustc_args.py
@@ -35,8 +35,6 @@
 except ImportError:
     import tomli as tomllib
 
-STRICT_LINTS = {"unknown_lints", "warnings"}
-
 
 class CargoTOML:
     tomldata: Mapping[Any, Any]
@@ -82,7 +80,7 @@ class LintFlag:
     priority: int
 
 
-def generate_lint_flags(cargo_toml: CargoTOML, strict_lints: bool) -> Iterable[str]:
+def generate_lint_flags(cargo_toml: CargoTOML) -> Iterable[str]:
     """Converts Cargo.toml lints to rustc -A/-D/-F/-W flags."""
 
     toml_lints = cargo_toml.lints
@@ -104,13 +102,6 @@ def generate_lint_flags(cargo_toml: CargoTOML, strict_lints: bool) -> Iterable[s
             else:
                 raise Exception(f"invalid level {level} for {prefix}{lint}")
 
-            if not (strict_lints and lint in STRICT_LINTS):
-                lint_list.append(LintFlag(flags=[flag, prefix + lint], priority=priority))
-
-    if strict_lints:
-        for lint in STRICT_LINTS:
-            lint_list.append(LintFlag(flags=["-D", lint], priority=1000000))
-
     lint_list.sort(key=lambda x: x.priority)
     for lint in lint_list:
         yield from lint.flags
@@ -187,13 +178,6 @@ def main() -> None:
         required=False,
         default="1.0.0",
     )
-    parser.add_argument(
-        "--strict-lints",
-        action="store_true",
-        dest="strict_lints",
-        help="apply stricter checks (for nightly Rust)",
-        default=False,
-    )
     args = parser.parse_args()
     if args.verbose:
         logging.basicConfig(level=logging.DEBUG)
@@ -207,7 +191,7 @@ def main() -> None:
         cargo_toml = CargoTOML(args.cargo_toml, None)
 
     if args.lints:
-        for tok in generate_lint_flags(cargo_toml, args.strict_lints):
+        for tok in generate_lint_flags(cargo_toml):
             print(tok)
 
     if rustc_version >= (1, 80):
-- 
2.51.1