rust: avoid assuming a particular `bindgen` build

`bindgen`'s logic to find `libclang` (via `clang-sys`) may change over
time, and depends on how it was built (e.g. Linux distributions may decide
to build it differently, and we are going to provide documentation on
installing it via distributions later in this series).

Therefore, clarify that `bindgen` may be built in several ways and
simplify the documentation by only mentioning the most prominent
environment variable (`LIBCLANG_PATH`) as an example on how to tweak the
search of the library at runtime (i.e. when `bindgen` is built as our
documentation explains). This also avoids duplicating the documentation,
like `bindgen` itself does (i.e. it refers to `clang-sys`).

Similarly, replace the test we had for this (which used the real program)
with a mocked one, to avoid depending on the particular build as well.

Tested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20240709160615.998336-8-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 15 insertions, 10 deletions

diff --git a/scripts/rust_is_available_test.py b/scripts/rust_is_available_test.py
index a255f79aafc2..0481aab862ec 100755
--- a/scripts/rust_is_available_test.py
+++ b/scripts/rust_is_available_test.py
@@ -55,10 +55,15 @@ else:
 
     @classmethod
     def generate_bindgen(cls, version_stdout, libclang_stderr):
+        if libclang_stderr is None:
+            libclang_case = f"raise SystemExit({cls.bindgen_default_bindgen_libclang_failure_exit_code})"
+        else:
+            libclang_case = f"print({repr(libclang_stderr)}, file=sys.stderr)"
+
         return cls.generate_executable(f"""#!/usr/bin/env python3
 import sys
 if "rust_is_available_bindgen_libclang.h" in " ".join(sys.argv):
-    print({repr(libclang_stderr)}, file=sys.stderr)
+    {libclang_case}
 else:
     print({repr(version_stdout)})
 """)
@@ -68,6 +73,10 @@ else:
         return cls.generate_bindgen(stdout, cls.bindgen_default_bindgen_libclang_stderr)
 
     @classmethod
+    def generate_bindgen_libclang_failure(cls):
+        return cls.generate_bindgen(cls.bindgen_default_bindgen_version_stdout, None)
+
+    @classmethod
     def generate_bindgen_libclang(cls, stderr):
         return cls.generate_bindgen(cls.bindgen_default_bindgen_version_stdout, stderr)
 
@@ -89,6 +98,7 @@ else:
         cls.rust_default_sysroot = subprocess.check_output(("rustc", "--print", "sysroot")).decode().strip()
 
         cls.bindgen_default_bindgen_version_stdout = f"bindgen {cls.bindgen_default_version}"
+        cls.bindgen_default_bindgen_libclang_failure_exit_code = 42
         cls.bindgen_default_bindgen_libclang_stderr = f"scripts/rust_is_available_bindgen_libclang.h:2:9: warning: clang version {cls.llvm_default_version} [-W#pragma-messages], err: false"
 
         cls.default_rustc = cls.generate_rustc(f"rustc {cls.rustc_default_version}")
@@ -227,15 +237,10 @@ else:
         self.assertIn(f"Rust bindings generator '{bindgen}' is too new. This may or may not work.", result.stderr)
 
     def test_bindgen_libclang_failure(self):
-        for env in (
-            { "LLVM_CONFIG_PATH": self.missing },
-            { "LIBCLANG_PATH": self.missing },
-            { "CLANG_PATH": self.missing },
-        ):
-            with self.subTest(env=env):
-                result = self.run_script(self.Expected.FAILURE, env | { "PATH": os.environ["PATH"], "BINDGEN": "bindgen" })
-                self.assertIn("Running 'bindgen' to check the libclang version (used by the Rust", result.stderr)
-                self.assertIn("bindings generator) failed with code ", result.stderr)
+        bindgen = self.generate_bindgen_libclang_failure()
+        result = self.run_script(self.Expected.FAILURE, { "BINDGEN": bindgen })
+        self.assertIn(f"Running '{bindgen}' to check the libclang version (used by the Rust", result.stderr)
+        self.assertIn(f"bindings generator) failed with code {self.bindgen_default_bindgen_libclang_failure_exit_code}. This may be caused by", result.stderr)
 
     def test_bindgen_libclang_unexpected_version(self):
         bindgen = self.generate_bindgen_libclang("scripts/rust_is_available_bindgen_libclang.h:2:9: warning: clang version unexpected [-W#pragma-messages], err: false")