scripts: port rustdoc_test_gen.py to Rust

JSON is not being used now, and the other script is already ported,
so it makes sense to port this one too.

With this, `CONFIG_RUST` does not introduce a Python dependency
(for building), and the remaining Python usage is in
`generate_rust_analyzer.py` which is not needed when building.

The performance difference is again more than an order of magnitude,
but in this case it does not matter much since it runs only once
compared to the builder. Nevertheless, at some point it is likely
there will be many more doctests and shaving a tine bit of time
never hurts.

In fact, from a clean build, this happens to be slower, due to
the compilation step of the script itself.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/Makefile

@@ -169,11 +169,12 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 		--no-run --crate-name kernel -Zunstable-options \
 		--test-builder $(objtree)/scripts/rustdoc_test_builder \
 		$< $(rustdoc_test_kernel_quiet); \
-	$(srctree)/scripts/rustdoc_test_gen.py
+	$(objtree)/scripts/rustdoc_test_gen
 
 %/doctests_kernel_generated.rs %/doctests_kernel_generated_kunit.c: \
     $(src)/kernel/lib.rs $(obj)/kernel.o \
-    $(objtree)/scripts/rustdoc_test_builder FORCE
+    $(objtree)/scripts/rustdoc_test_builder \
+    $(objtree)/scripts/rustdoc_test_gen FORCE
 	$(call if_changed,rustdoc_test_kernel)
 
 # We cannot use `-Zpanic-abort-tests` because some tests are dynamic,

scripts/.gitignore

@@ -7,6 +7,7 @@
 /module.lds
 /recordmcount
 /rustdoc_test_builder
+/rustdoc_test_gen
 /sign-file
 /sorttable
 /unifdef

scripts/Makefile

@@ -12,10 +12,12 @@ hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
 hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
 hostprogs-always-$(CONFIG_RUST)				+= \
 	generate_rust_target \
-	rustdoc_test_builder
+	rustdoc_test_builder \
+	rustdoc_test_gen
 
 generate_rust_target-rust := y
 rustdoc_test_builder-rust := y
+rustdoc_test_gen-rust := y
 
 HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
 HOSTLDLIBS_sorttable = -lpthread

scripts/rustdoc_test_gen.py renamed to scripts/rustdoc_test_gen.rs

@@ -1,21 +1,37 @@
-#!/usr/bin/env python3
-# SPDX-License-Identifier: GPL-2.0
-"""rustdoc_test_gen - Generates KUnit tests from saved `rustdoc`-generated tests.
-"""
-
-import os
-import pathlib
-
-RUST_DIR = pathlib.Path("rust")
-TESTS_DIR = RUST_DIR / "test" / "doctests" / "kernel"
-
-RUST_FILE = RUST_DIR / "doctests_kernel_generated.rs"
-C_FILE = RUST_DIR / "doctests_kernel_generated_kunit.c"
-
-RUST_TEMPLATE_TEST = """
-/// Generated `{test_name}` KUnit test case from a Rust documentation test.
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generates KUnit tests from saved `rustdoc`-generated tests.
+
+use std::io::{BufWriter, Read, Write};
+use std::{fs, fs::File};
+
+fn main() {
+    let mut dirs = fs::read_dir("rust/test/doctests/kernel")
+        .unwrap()
+        .map(|p| p.unwrap().path())
+        .collect::<Vec<_>>();
+    dirs.sort();
+
+    let mut rust_tests = String::new();
+    let mut c_test_declarations = String::new();
+    let mut c_test_cases = String::new();
+    let mut content = String::new();
+    for path in dirs {
+        content.clear();
+
+        File::open(path)
+            .unwrap()
+            .read_to_string(&mut content)
+            .unwrap();
+
+        let (name, body) = content.split_once("\n").unwrap();
+
+        use std::fmt::Write;
+        write!(
+            rust_tests,
+            r#"/// Generated `{name}` KUnit test case from a Rust documentation test.
 #[no_mangle]
-pub fn {test_name}(__kunit_test: *mut kernel::bindings::kunit) {{
+pub fn {name}(__kunit_test: *mut kernel::bindings::kunit) {{
     /// Provides mutual exclusion (see `# Implementation` notes).
     static __KUNIT_TEST_MUTEX: kernel::sync::smutex::Mutex<()> =
         kernel::sync::smutex::Mutex::new(());
@@ -55,12 +71,26 @@
     use kernel::prelude::*;
 
     {{
-        {test_body}
+        {body}
         main();
     }}
 }}
-"""
-RUST_TEMPLATE = """// SPDX-License-Identifier: GPL-2.0
+
+"#
+        )
+        .unwrap();
+
+        write!(c_test_declarations, "void {name}(struct kunit *);\n").unwrap();
+        write!(c_test_cases, "    KUNIT_CASE({name}),\n").unwrap();
+    }
+
+    let rust_tests = rust_tests.trim();
+    let c_test_declarations = c_test_declarations.trim();
+    let c_test_cases = c_test_cases.trim();
+
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated.rs").unwrap()),
+        r#"// SPDX-License-Identifier: GPL-2.0
 
 //! `kernel` crate documentation tests.
 
@@ -98,14 +128,16 @@
 // an `AtomicPtr` to hold the context (though each test only writes once before
 // threads may be created).
 
-const __LOG_PREFIX: &[u8] = b"rust_kernel_doctests\\0";
+const __LOG_PREFIX: &[u8] = b"rust_kernel_doctests\0";
 
 {rust_tests}
-"""
+"#
+    )
+    .unwrap();
 
-C_TEMPLATE_TEST_DECLARATION = "void {test_name}(struct kunit *);\n"
-C_TEMPLATE_TEST_CASE = "    KUNIT_CASE({test_name}),\n"
-C_TEMPLATE = """// SPDX-License-Identifier: GPL-2.0
+    write!(
+        BufWriter::new(File::create("rust/doctests_kernel_generated_kunit.c").unwrap()),
+        r#"// SPDX-License-Identifier: GPL-2.0
 /*
  * `kernel` crate documentation tests.
  */
@@ -127,36 +159,7 @@
 kunit_test_suite(test_suite);
 
 MODULE_LICENSE("GPL");
-"""
-
-def main():
-    rust_tests = ""
-    c_test_declarations = ""
-    c_test_cases = ""
-    for filename in sorted(os.listdir(TESTS_DIR)):
-        with open(TESTS_DIR / filename, "r") as fd:
-            (test_name, test_body) = fd.read().split('\n', 1)
-            rust_tests += RUST_TEMPLATE_TEST.format(
-                test_name = test_name,
-                test_body = test_body
-            )
-            c_test_declarations += C_TEMPLATE_TEST_DECLARATION.format(
-                test_name = test_name
-            )
-            c_test_cases += C_TEMPLATE_TEST_CASE.format(
-                test_name = test_name
-            )
-
-    with open(RUST_FILE, "w") as fd:
-        fd.write(RUST_TEMPLATE.format(
-            rust_tests = rust_tests.strip(),
-        ))
-
-    with open(C_FILE, "w") as fd:
-        fd.write(C_TEMPLATE.format(
-            c_test_declarations=c_test_declarations.strip(),
-            c_test_cases=c_test_cases.strip(),
-        ))
-
-if __name__ == "__main__":
-    main()
+"#
+    )
+    .unwrap();
+}