Rust: allow formatting without linting, fix codegen runfiles path

`lint.py --format-only` gives the upcoming `just format` verb a way to
reformat without failing on pre-existing lint findings.

codegen.sh looked up its runfiles via `external/ql+`, which only resolves
in a main-repository layout. `../ql+` works from both, so codegen keeps
working when the repository is consumed as a bazel dependency.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: redsun82

rust/codegen/codegen.sh

@@ -2,7 +2,7 @@
 
 set -eu
 
-source misc/bazel/runfiles.sh 2>/dev/null || source external/ql+/misc/bazel/runfiles.sh
+source misc/bazel/runfiles.sh 2>/dev/null || source ../ql+/misc/bazel/runfiles.sh
 
 ast_generator="$(rlocation "$1")"
 grammar_file="$(rlocation "$2")"

rust/lint.py

@@ -4,6 +4,15 @@
 import pathlib
 import shutil
 import sys
+import argparse
+
+
+def options():
+    parser = argparse.ArgumentParser(description="lint rust language pack code")
+    parser.add_argument(
+        "--format-only", action="store_true", help="Only apply formatting"
+    )
+    return parser.parse_args()
 
 
 def tool(name):
@@ -12,27 +21,33 @@ def tool(name):
     return ret
 
 
-this_dir = pathlib.Path(__file__).resolve().parent
+def main():
+    args = options()
+    this_dir = pathlib.Path(__file__).resolve().parent
+
+    cargo = tool("cargo")
+    bazel = tool("bazel")
 
-cargo = tool("cargo")
-bazel = tool("bazel")
+    runs = []
 
-runs = []
+    def run(tool, args, *, cwd=this_dir):
+        print("+", tool, args)
+        runs.append(subprocess.run([tool] + args.split(), cwd=cwd))
 
 
-def run(tool, args, *, cwd=this_dir):
-    print("+", tool, args)
-    runs.append(subprocess.run([tool] + args.split(), cwd=cwd))
+    # make sure bazel-provided sources are put in tree for `cargo` to work with them
+    run(bazel, "run ast-generator:inject-sources")
+    run(cargo, "fmt --all --quiet")
 
+    if not args.format_only:
+        for manifest in this_dir.rglob("Cargo.toml"):
+            if not manifest.is_relative_to(this_dir / "ql") and not manifest.is_relative_to(this_dir / "integration-tests"):
+                run(cargo,
+                    "clippy --fix --allow-dirty --allow-staged --quiet -- -D warnings",
+                    cwd=manifest.parent)
 
-# make sure bazel-provided sources are put in tree for `cargo` to work with them
-run(bazel, "run ast-generator:inject-sources")
-run(cargo, "fmt --all --quiet")
+    return max(r.returncode for r in runs)
 
-for manifest in this_dir.rglob("Cargo.toml"):
-    if not manifest.is_relative_to(this_dir / "ql") and not manifest.is_relative_to(this_dir / "integration-tests"):
-        run(cargo,
-            "clippy --fix --allow-dirty --allow-staged --quiet -- -D warnings",
-            cwd=manifest.parent)
 
-sys.exit(max(r.returncode for r in runs))
+if __name__ == "__main__":
+    sys.exit(main())