Re: [PATCH 2/2] rust: doctest: trim function name for reproducbility

[Gary Guo]

On Sun Jun 14, 2026 at 8:07 AM BST, David Gow wrote:
> Le 13/06/2026 à 10:04 PM, Gary Guo a écrit :
>> From: Gary Guo <gary@xxxxxxxxxxx>
>> 
>> Currently rustdoc will generate function names like
>> "_doctest_main__home_gary_Projects_linux_rust_kernel_io_rs_824_0" for a
>> doctest located at rust/kernel/io.rs:824, when building with separate
>> outdir using `O=`. This creates overlong symbol names and is also not
>> reproducible.
>> 
>> Fix it by doing a custom remapping to trim it to something like
>> `_doctest_main_rust_kernel_io_rs_824_0`.
>> 
>> Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
>> ---
>
> Hi Gary,
>
> This seems to break older versions of rustc. For example, with
> rust 1.93.1, the build now fails with errors like:
>
> ERROR:root:error[E0425]: cannot find function `_doctest_main_rust_kernel_alloc_allocator_rs_176_0` in this scope
>   --> rust/doctests_kernel_generated.rs:74:27
>    |
> 74 | } let test_return_value = _doctest_main_rust_kernel_alloc_allocator_rs_176_0(); assert!(test_return_value.is_ok()); }
>    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in this scope
>
>
> Am I missing something? I'm using kunit.py to build:
> ./tools/testing/kunit/kunit.py run --kconfig_add CONFIG_RUST=y rust_doctests_kernel
>
> Seems to be working okay with 1.96, though.

It looks like upstream rustdoc is using fully qualified path from 1.87+, so the
replacement doesn't find it anymore. Not sure why it works in 1.96, though.

Sashiko suggested doing a full text replacement which I think makes more sense
anyway and would work for all versions (and also for unit-returning functions).
Will do it for the next version.

Best,
Gary

>
> Cheers,
> -- David
>
>>  scripts/rustdoc_test_builder.rs | 14 +++++++++-----
>>  1 file changed, 9 insertions(+), 5 deletions(-)
>> 
>> diff --git a/scripts/rustdoc_test_builder.rs b/scripts/rustdoc_test_builder.rs
>> index 2b1f9ba01839..fda7284355f8 100644
>> --- a/scripts/rustdoc_test_builder.rs
>> +++ b/scripts/rustdoc_test_builder.rs
>> @@ -47,11 +47,18 @@ fn main() {
>>          })
>>          .expect("No test function found in `rustdoc`'s output.");
>>  
>> +    // Figure out a smaller test name based on the generated function name.
>> +    let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1;
>> +
>> +    // The rustdoc function name can include the absolute path when building with `O=` which is
>> +    // undesireable and create overlong symbol names. Remap it to relative path.
>> +    let trimmed_function_name = format!("_doctest_main_rust_kernel_{name}");
>> +
>>      // Qualify `Result` to avoid the collision with our own `Result` coming from the prelude.
>>      let body = body.replace(
>>          &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"),
>>          &format!(
>> -            "{rustdoc_function_name}() -> ::core::result::Result<(), impl ::core::fmt::Debug> {{"
>> +            "{trimmed_function_name}() -> ::core::result::Result<(), impl ::core::fmt::Debug> {{"
>>          ),
>>      );
>>  
>> @@ -62,12 +69,9 @@ fn main() {
>>      // We save the result in a variable so that the failed assertion message looks nicer.
>>      let body = body.replace(
>>          &format!("}} {rustdoc_function_name}().unwrap() }}"),
>> -        &format!("}} let test_return_value = {rustdoc_function_name}(); assert!(test_return_value.is_ok()); }}"),
>> +        &format!("}} let test_return_value = {trimmed_function_name}(); assert!(test_return_value.is_ok()); }}"),
>>      );
>>  
>> -    // Figure out a smaller test name based on the generated function name.
>> -    let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1;
>> -
>>      let path = format!("rust/test/doctests/kernel/{name}");
>>  
>>      std::fs::write(path, body.as_bytes()).unwrap();