rust: doctest: fix incorrect pattern in replacement

From: Gary Guo <[email protected]>

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 <[email protected]>

---

 scripts/rustdoc_test_builder.rs | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

scripts/rustdoc_test_builder.rs +9 -5

index 2b1f9ba01839..fda7284355f8 100644
@@ -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();

Le 13/06/2026 à 10:04 PM, Gary Guo a écrit :

Quoted 8 lines

From: Gary Guo <[email protected]>

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.

Quoted 5 lines

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 <[email protected]>

---

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

Quoted 41 lines

 scripts/rustdoc_test_builder.rs | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

scripts/rustdoc_test_builder.rs +9 -5

index 2b1f9ba01839..fda7284355f8 100644
@@ -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();