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1// SPDX-License-Identifier: GPL-2.0
2
3//! Test builder for `rustdoc`-generated tests.
4//!
5//! This script is a hack to extract the test from `rustdoc`'s output. Ideally, `rustdoc` would
6//! have an option to generate this information instead, e.g. as JSON output.
7//!
8//! The `rustdoc`-generated test names look like `{file}_{line}_{number}`, e.g.
9//! `...path_rust_kernel_sync_arc_rs_42_0`. `number` is the "test number", needed in cases like
10//! a macro that expands into items with doctests is invoked several times within the same line.
11//!
12//! However, since these names are used for bisection in CI, the line number makes it not stable
13//! at all. In the future, we would like `rustdoc` to give us the Rust item path associated with
14//! the test, plus a "test number" (for cases with several examples per item) and generate a name
15//! from that. For the moment, we generate ourselves a new name, `{file}_{number}` instead, in
16//! the `gen` script (done there since we need to be aware of all the tests in a given file).
17
18use std::io::Read;
19
20fn main() {
21 let mut stdin = std::io::stdin().lock();
22 let mut body = String::new();
23 stdin.read_to_string(&mut body).unwrap();
24
25 // Find the generated function name looking for the inner function inside `main()`.
26 //
27 // The line we are looking for looks like one of the following:
28 //
29 // ```
30 // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_28_0() {
31 // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl core::fmt::Debug> {
32 // ```
33 //
34 // It should be unlikely that doctest code matches such lines (when code is formatted properly).
35 let rustdoc_function_name = body
36 .lines()
37 .find_map(|line| {
38 Some(
39 line.split_once("fn main() {")?
40 .1
41 .split_once("fn ")?
42 .1
43 .split_once("()")?
44 .0,
45 )
46 .filter(|x| x.chars().all(|c| c.is_alphanumeric() || c == '_'))
47 })
48 .expect("No test function found in `rustdoc`'s output.");
49
50 // Replicate `rustdoc` 1.87+ behaviour [1] by fully qualifying `Result` to avoid the collision
51 // with our own `Result` coming from the prelude.
52 //
53 // [1]: https://github.com/rust-lang/rust/pull/137807
54 //
55 // TODO: Remove this when MSRV is bumped above 1.87.
56 let body = body.replace(
57 &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"),
58 // This intentionally does not use absolute paths to match `rustdoc` 1.87 behaviour.
59 &format!("{rustdoc_function_name}() -> core::result::Result<(), impl core::fmt::Debug> {{"),
60 );
61
62 // For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on
63 // the return value to check there were no returned errors. Instead, we use our assert macro
64 // since we want to just fail the test, not panic the kernel.
65 //
66 // We save the result in a variable so that the failed assertion message looks nicer.
67 let body = body.replace(
68 &format!("}} {rustdoc_function_name}().unwrap() }}"),
69 &format!("}} let test_return_value = {rustdoc_function_name}(); assert!(test_return_value.is_ok()); }}"),
70 );
71
72 // Figure out a smaller test name based on the generated function name.
73 let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1;
74
75 let path = format!("rust/test/doctests/kernel/{name}");
76
77 std::fs::write(path, body.as_bytes()).unwrap();
78}