[PATCH 1/2] rust: doctest: fix incorrect pattern in replacement

[PATCH 1/2] rust: doctest: fix incorrect pattern in replacement

[Gary Guo]

From: Gary Guo <gary@garyguo.net>

The `-> Result<(), impl core::fmt::Debug>` string is generated by rustdoc
and by adding "::" into the string it no longer finds anything, and making
the line useless. Remove the "::" in the pattern (but keep it in the
replacement result).

Fixes: de7cd3e4d638 ("rust: use absolute paths in macros referencing core and kernel")
Signed-off-by: Gary Guo <gary@garyguo.net>
---
 scripts/rustdoc_test_builder.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/rustdoc_test_builder.rs b/scripts/rustdoc_test_builder.rs
index f7540bcf595a..2b1f9ba01839 100644
--- a/scripts/rustdoc_test_builder.rs
+++ b/scripts/rustdoc_test_builder.rs
@@ -49,7 +49,7 @@ fn main() {
 
     // 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}() -> Result<(), impl core::fmt::Debug> {{"),
         &format!(
             "{rustdoc_function_name}() -> ::core::result::Result<(), impl ::core::fmt::Debug> {{"
         ),

base-commit: abe651837cb394f76d738a7a747322fca3bf17ba
-- 
2.54.0

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

[Gary Guo]

From: Gary Guo <gary@garyguo.net>

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@garyguo.net>
---
 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();
-- 
2.54.0

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

[David Gow]

Le 13/06/2026 à 10:04 PM, Gary Guo a écrit :
> From: Gary Guo <gary@garyguo.net>
> 
> 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@garyguo.net>
> ---

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.

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();

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@garyguo.net>
>> 
>> 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@garyguo.net>
>> ---
>
> 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();