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

[Gary Guo]

From: Gary Guo <ga...@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 <ga...@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

[Gary Guo]

From: Gary Guo <ga...@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 <ga...@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

[Gary Guo]

From: Gary Guo <ga...@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. Omit it in the replacement too, for
consistency with upstream rustdoc.

Fixes: de7cd3e4d638 ("rust: use absolute paths in macros referencing core and kernel")
Signed-off-by: Gary Guo <ga...@garyguo.net>
--

Changes in v2:
- Update comments too
- Stops using :: in the replacement too to be consistent with upstream
rustdoc
---
scripts/rustdoc_test_builder.rs | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/scripts/rustdoc_test_builder.rs b/scripts/rustdoc_test_builder.rs
index f7540bcf595a..5457679c12f9 100644
--- a/scripts/rustdoc_test_builder.rs
+++ b/scripts/rustdoc_test_builder.rs
@@ -28,7 +28,7 @@ fn main() {
//
// ```
// fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_28_0() {
- // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl ::core::fmt::Debug> {
+ // fn main() { #[allow(non_snake_case)] fn _doctest_main_rust_kernel_file_rs_37_0() -> Result<(), impl core::fmt::Debug> {
// ```
//
// It should be unlikely that doctest code matches such lines (when code is formatted properly).
@@ -47,12 +47,14 @@ fn main() {

})
.expect("No test function found in `rustdoc`'s output.");

- // Qualify `Result` to avoid the collision with our own `Result` coming from the prelude.
+ // Replicate rustdoc 1.87+ behaviour by fully qualify `Result` (to avoid the collision with our
+ // own `Result` coming from the prelude).
+ //
+ // TODO: Remove this when MSRV is bumped above 1.87.
let body = body.replace(
- &format!("{rustdoc_function_name}() -> Result<(), impl ::core::fmt::Debug> {{"),
- &format!(

- "{rustdoc_function_name}() -> ::core::result::Result<(), impl ::core::fmt::Debug> {{"

- ),
+ &format!("{rustdoc_function_name}() -> Result<(), impl core::fmt::Debug> {{"),
+ // This intentionally does not use absolute paths to match rustdoc 1.87 behaviour.
+ &format!("{rustdoc_function_name}() -> core::result::Result<(), impl core::fmt::Debug> {{"),
);

// For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on

base-commit: c425609d6ac4012c8bbf01ec2e10e801b1923a7b
prerequisite-patch-id: 0000000000000000000000000000000000000000
--
2.54.0

[Gary Guo]

From: Gary Guo <ga...@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 <ga...@garyguo.net>
---

Changes in v2:
- Do an unconditional replacement to cover all cases.
---
scripts/rustdoc_test_builder.rs | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/scripts/rustdoc_test_builder.rs b/scripts/rustdoc_test_builder.rs
index 5457679c12f9..79cef75f5af3 100644
--- a/scripts/rustdoc_test_builder.rs
+++ b/scripts/rustdoc_test_builder.rs
@@ -70,6 +70,11 @@ fn main() {

// 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 use relative path.

+ let trimmed_function_name = format!("_doctest_main_rust_kernel_{name}");

+ let body = body.replace(&rustdoc_function_name, &trimmed_function_name);
+

[Miguel Ojeda]

On Tue, Jun 16, 2026 at 3:27 PM Gary Guo <ga...@kernel.org> wrote:
>
> 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. Omit it in the replacement too, for
> consistency with upstream rustdoc.
>
> Fixes: de7cd3e4d638 ("rust: use absolute paths in macros referencing core and kernel")
> Signed-off-by: Gary Guo <ga...@garyguo.net>

Applied to `rust-fixes` -- thanks!

[ Improved comments for consistency. Reworded to drop changelog and to
fix typo. - Miguel ]

While it doesn't happen to hurt much at the moment, the change here
was not intended and we should be able to easily backport it, so:

Cc: sta...@vger.kernel.org

Cheers,
Miguel

[Miguel Ojeda]

On Fri, Jun 19, 2026 at 9:35 AM Miguel Ojeda
<miguel.oje...@gmail.com> wrote:
>
> [ Improved comments for consistency. Reworded to drop changelog and to
> fix typo. - Miguel ]

Actually, I just added a link to the comment to the upstream `rustdoc`
PR for context.

Cheers,
Miguel