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Filename : rustdoc_test_gen.rs
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// SPDX-License-Identifier: GPL-2.0

//! Generates KUnit tests from saved `rustdoc`-generated tests.
//!
//! KUnit passes a context (`struct kunit *`) to each test, which should be forwarded to the other
//! KUnit functions and macros.
//!
//! However, we want to keep this as an implementation detail because:
//!
//!   - Test code should not care about the implementation.
//!
//!   - Documentation looks worse if it needs to carry extra details unrelated to the piece
//!     being described.
//!
//!   - Test code should be able to define functions and call them, without having to carry
//!     the context.
//!
//!   - Later on, we may want to be able to test non-kernel code (e.g. `core`, `alloc` or
//!     third-party crates) which likely use the standard library `assert*!` macros.
//!
//! For this reason, instead of the passed context, `kunit_get_current_test()` is used instead
//! (i.e. `current->kunit_test`).
//!
//! Note that this means other threads/tasks potentially spawned by a given test, if failing, will
//! report the failure in the kernel log but will not fail the actual test. Saving the pointer in
//! e.g. a `static` per test does not fully solve the issue either, because currently KUnit does
//! not support assertions (only expectations) from other tasks. Thus leave that feature for
//! the future, which simplifies the code here too. We could also simply not allow `assert`s in
//! other tasks, but that seems overly constraining, and we do want to support them, eventually.

use std::{
    fs,
    fs::File,
    io::{BufWriter, Read, Write},
    path::{Path, PathBuf},
};

/// Find the real path to the original file based on the `file` portion of the test name.
///
/// `rustdoc` generated `file`s look like `sync_locked_by_rs`. Underscores (except the last one)
/// may represent an actual underscore in a directory/file, or a path separator. Thus the actual
/// file might be `sync_locked_by.rs`, `sync/locked_by.rs`, `sync_locked/by.rs` or
/// `sync/locked/by.rs`. This function walks the file system to determine which is the real one.
///
/// This does require that ambiguities do not exist, but that seems fair, especially since this is
/// all supposed to be temporary until `rustdoc` gives us proper metadata to build this. If such
/// ambiguities are detected, they are diagnosed and the script panics.
fn find_real_path<'a>(srctree: &Path, valid_paths: &'a mut Vec<PathBuf>, file: &str) -> &'a str {
    valid_paths.clear();

    let potential_components: Vec<&str> = file.strip_suffix("_rs").unwrap().split('_').collect();

    find_candidates(srctree, valid_paths, Path::new(""), &potential_components);
    fn find_candidates(
        srctree: &Path,
        valid_paths: &mut Vec<PathBuf>,
        prefix: &Path,
        potential_components: &[&str],
    ) {
        // The base case: check whether all the potential components left, joined by underscores,
        // is a file.
        let joined_potential_components = potential_components.join("_") + ".rs";
        if srctree
            .join("rust/kernel")
            .join(prefix)
            .join(&joined_potential_components)
            .is_file()
        {
            // Avoid `srctree` here in order to keep paths relative to it in the KTAP output.
            valid_paths.push(
                Path::new("rust/kernel")
                    .join(prefix)
                    .join(joined_potential_components),
            );
        }

        // In addition, check whether each component prefix, joined by underscores, is a directory.
        // If not, there is no need to check for combinations with that prefix.
        for i in 1..potential_components.len() {
            let (components_prefix, components_rest) = potential_components.split_at(i);
            let prefix = prefix.join(components_prefix.join("_"));
            if srctree.join("rust/kernel").join(&prefix).is_dir() {
                find_candidates(srctree, valid_paths, &prefix, components_rest);
            }
        }
    }

    assert!(
        valid_paths.len() > 0,
        "No path candidates found. This is likely a bug in the build system, or some files went \
        away while compiling."
    );

    if valid_paths.len() > 1 {
        eprintln!("Several path candidates found:");
        for path in valid_paths {
            eprintln!("    {path:?}");
        }
        panic!(
            "Several path candidates found, please resolve the ambiguity by renaming a file or \
            folder."
        );
    }

    valid_paths[0].to_str().unwrap()
}

fn main() {
    let srctree = std::env::var("srctree").unwrap();
    let srctree = Path::new(&srctree);

    let mut paths = fs::read_dir("rust/test/doctests/kernel")
        .unwrap()
        .map(|entry| entry.unwrap().path())
        .collect::<Vec<_>>();

    // Sort paths.
    paths.sort();

    let mut rust_tests = String::new();
    let mut c_test_declarations = String::new();
    let mut c_test_cases = String::new();
    let mut body = String::new();
    let mut last_file = String::new();
    let mut number = 0;
    let mut valid_paths: Vec<PathBuf> = Vec::new();
    let mut real_path: &str = "";
    for path in paths {
        // The `name` follows the `{file}_{line}_{number}` pattern (see description in
        // `scripts/rustdoc_test_builder.rs`). Discard the `number`.
        let name = path.file_name().unwrap().to_str().unwrap().to_string();

        // Extract the `file` and the `line`, discarding the `number`.
        let (file, line) = name.rsplit_once('_').unwrap().0.rsplit_once('_').unwrap();

        // Generate an ID sequence ("test number") for each one in the file.
        if file == last_file {
            number += 1;
        } else {
            number = 0;
            last_file = file.to_string();

            // Figure out the real path, only once per file.
            real_path = find_real_path(srctree, &mut valid_paths, file);
        }

        // Generate a KUnit name (i.e. test name and C symbol) for this test.
        //
        // We avoid the line number, like `rustdoc` does, to make things slightly more stable for
        // bisection purposes. However, to aid developers in mapping back what test failed, we will
        // print a diagnostics line in the KTAP report.
        let kunit_name = format!("rust_doctest_kernel_{file}_{number}");

        // Read the test's text contents to dump it below.
        body.clear();
        File::open(path).unwrap().read_to_string(&mut body).unwrap();

        // Calculate how many lines before `main` function (including the `main` function line).
        let body_offset = body
            .lines()
            .take_while(|line| !line.contains("fn main() {"))
            .count()
            + 1;

        use std::fmt::Write;
        write!(
            rust_tests,
            r#"/// Generated `{name}` KUnit test case from a Rust documentation test.
#[no_mangle]
pub extern "C" fn {kunit_name}(__kunit_test: *mut kernel::bindings::kunit) {{
    /// Overrides the usual [`assert!`] macro with one that calls KUnit instead.
    #[allow(unused)]
    macro_rules! assert {{
        ($cond:expr $(,)?) => {{{{
            kernel::kunit_assert!("{kunit_name}", "{real_path}", __DOCTEST_ANCHOR - {line}, $cond);
        }}}}
    }}

    /// Overrides the usual [`assert_eq!`] macro with one that calls KUnit instead.
    #[allow(unused)]
    macro_rules! assert_eq {{
        ($left:expr, $right:expr $(,)?) => {{{{
            kernel::kunit_assert_eq!("{kunit_name}", "{real_path}", __DOCTEST_ANCHOR - {line}, $left, $right);
        }}}}
    }}

    // Many tests need the prelude, so provide it by default.
    #[allow(unused)]
    use kernel::prelude::*;

    // Unconditionally print the location of the original doctest (i.e. rather than the location in
    // the generated file) so that developers can easily map the test back to the source code.
    //
    // This information is also printed when assertions fail, but this helps in the successful cases
    // when the user is running KUnit manually, or when passing `--raw_output` to `kunit.py`.
    //
    // This follows the syntax for declaring test metadata in the proposed KTAP v2 spec, which may
    // be used for the proposed KUnit test attributes API. Thus hopefully this will make migration
    // easier later on.
    kernel::kunit::info(format_args!("    # {kunit_name}.location: {real_path}:{line}\n"));

    /// The anchor where the test code body starts.
    #[allow(unused)]
    static __DOCTEST_ANCHOR: i32 = core::line!() as i32 + {body_offset} + 1;
    {{
        {body}
        main();
    }}
}}

"#
        )
        .unwrap();

        write!(c_test_declarations, "void {kunit_name}(struct kunit *);\n").unwrap();
        write!(c_test_cases, "    KUNIT_CASE({kunit_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#"//! `kernel` crate documentation tests.

const __LOG_PREFIX: &[u8] = b"rust_doctests_kernel\0";

{rust_tests}
"#
    )
    .unwrap();

    write!(
        BufWriter::new(File::create("rust/doctests_kernel_generated_kunit.c").unwrap()),
        r#"/*
 * `kernel` crate documentation tests.
 */

#include <kunit/test.h>

{c_test_declarations}

static struct kunit_case test_cases[] = {{
    {c_test_cases}
    {{ }}
}};

static struct kunit_suite test_suite = {{
    .name = "rust_doctests_kernel",
    .test_cases = test_cases,
}};

kunit_test_suite(test_suite);

MODULE_LICENSE("GPL");
"#
    )
    .unwrap();
}