Use new --output-format=doctest rustdoc command line flag to improve doctest handling

GuillaumeGomez · intel-lab-lkp · commit 08f87593efd3 · 2025-06-17T22:05:06.000+08:00
The goal of this patch is to remove the use of 2 unstable rustdoc features (`--no-run` and `--test-builder`) and replace it with a stable feature: `--output-format=doctest`, which was added in rust-lang/rust#134531. Before this patch, the code was using very hacky methods in order to retrieve doctests, modify them as needed and then concatenate all of them in one file. Now, with this new flag, it instead asks rustdoc to provide the doctests code with their associated information such as file path and line number. Signed-off-by: Guillaume Gomez <guillaume1.gomez@gmail.com>
diff --git a/rust/Makefile b/rust/Makefile
@@ -205,14 +205,15 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 	rm -rf $(objtree)/$(obj)/test/doctests/kernel; \
 	mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
 	OBJTREE=$(abspath $(objtree)) \
-	$(RUSTDOC) --test $(filter-out --remap-path-prefix=%,$(rust_flags)) \
+	$(RUSTDOC) --output-format=doctest $(filter-out --remap-path-prefix=%,$(rust_flags)) \
 		-L$(objtree)/$(obj) --extern ffi --extern pin_init \
 		--extern kernel --extern build_error --extern macros \
 		--extern bindings --extern uapi \
-		--no-run --crate-name kernel -Zunstable-options \
+		--crate-name kernel -Zunstable-options \
 		--sysroot=/dev/null \
 		--test-builder $(objtree)/scripts/rustdoc_test_builder \
-		$< $(rustdoc_test_kernel_quiet); \
+		$< $(rustdoc_test_kernel_quiet) > rustdoc.json; \
+	cat rustdoc.json | $(objtree)/scripts/rustdoc_test_builder; \
 	$(objtree)/scripts/rustdoc_test_gen
 
 %/doctests_kernel_generated.rs %/doctests_kernel_generated_kunit.c: \
diff --git a/scripts/json.rs b/scripts/json.rs
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! JSON parser used to parse rustdoc output when retrieving doctests.
+
+use std::collections::HashMap;
+use std::iter::Peekable;
+use std::str::FromStr;
+
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) enum JsonValue {
+    Object(HashMap<String, JsonValue>),
+    String(String),
+    Number(i32),
+    Bool(bool),
+    Array(Vec<JsonValue>),
+    Null,
+}
+
+fn parse_ident<I: Iterator<Item = char>>(
+    iter: &mut I,
+    output: JsonValue,
+    ident: &str,
+) -> Result<JsonValue, String> {
+    let mut ident_iter = ident.chars().skip(1);
+
+    loop {
+        let i = ident_iter.next();
+        if i.is_none() {
+            return Ok(output);
+        }
+        let c = iter.next();
+        if i != c {
+            if let Some(c) = c {
+                return Err(format!("Unexpected character `{c}` when parsing `{ident}`"));
+            }
+            return Err(format!("Missing character when parsing `{ident}`"));
+        }
+    }
+}
+
+fn parse_string<I: Iterator<Item = char>>(iter: &mut I) -> Result<JsonValue, String> {
+    let mut out = String::new();
+
+    while let Some(c) = iter.next() {
+        match c {
+            '\\' => {
+                let Some(c) = iter.next() else { break };
+                match c {
+                    '"' | '\\' | '/' => out.push(c),
+                    'b' => out.push(char::from(0x8u8)),
+                    'f' => out.push(char::from(0xCu8)),
+                    't' => out.push('\t'),
+                    'r' => out.push('\r'),
+                    'n' => out.push('\n'),
+                    _ => {
+                        // This code doesn't handle codepoints so we put the string content as is.
+                        out.push('\\');
+                        out.push(c);
+                    }
+                }
+            }
+            '"' => {
+                return Ok(JsonValue::String(out));
+            }
+            _ => out.push(c),
+        }
+    }
+    Err(format!("Unclosed JSON string `{out}`"))
+}
+
+fn parse_number<I: Iterator<Item = char>>(
+    iter: &mut Peekable<I>,
+    digit: char,
+) -> Result<JsonValue, String> {
+    let mut nb = String::new();
+
+    nb.push(digit);
+    loop {
+        // We peek next character to prevent taking it from the iterator in case it's a comma.
+        if matches!(iter.peek(), Some(',' | '}' | ']')) {
+            break;
+        }
+        let Some(c) = iter.next() else { break };
+        if c.is_whitespace() {
+            break;
+        } else if !c.is_ascii_digit() {
+            return Err(format!("Error when parsing number `{nb}`: found `{c}`"));
+        }
+        nb.push(c);
+    }
+    i32::from_str(&nb)
+        .map(|nb| JsonValue::Number(nb))
+        .map_err(|error| format!("Invalid number: `{error}`"))
+}
+
+fn parse_array<I: Iterator<Item = char>>(iter: &mut Peekable<I>) -> Result<JsonValue, String> {
+    let mut values = Vec::new();
+
+    'main: loop {
+        let Some(c) = iter.next() else {
+            return Err("Unclosed array".to_string());
+        };
+        if c.is_whitespace() {
+            continue;
+        } else if c == ']' {
+            break;
+        }
+        values.push(parse(iter, c)?);
+        while let Some(c) = iter.next() {
+            if c.is_whitespace() {
+                continue;
+            } else if c == ',' {
+                break;
+            } else if c == ']' {
+                break 'main;
+            } else {
+                return Err(format!("Unexpected `{c}` when parsing array"));
+            }
+        }
+    }
+    Ok(JsonValue::Array(values))
+}
+
+fn parse_object<I: Iterator<Item = char>>(iter: &mut Peekable<I>) -> Result<JsonValue, String> {
+    let mut values = HashMap::new();
+
+    'main: loop {
+        let Some(c) = iter.next() else {
+            return Err("Unclosed object".to_string());
+        };
+        let key;
+        if c.is_whitespace() {
+            continue;
+        } else if c == '"' {
+            let JsonValue::String(k) = parse_string(iter)? else {
+                unreachable!()
+            };
+            key = k;
+        } else if c == '}' {
+            break;
+        } else {
+            return Err(format!("Expected `\"` when parsing Object, found `{c}`"));
+        }
+
+        // We then get the `:` separator.
+        loop {
+            let Some(c) = iter.next() else {
+                return Err(format!("Missing value after key `{key}`"));
+            };
+            if c.is_whitespace() {
+                continue;
+            } else if c == ':' {
+                break;
+            } else {
+                return Err(format!(
+                    "Expected `:` after key, found `{c}` when parsing object"
+                ));
+            }
+        }
+        // Then the value.
+        let value = loop {
+            let Some(c) = iter.next() else {
+                return Err(format!("Missing value after key `{key}`"));
+            };
+            if c.is_whitespace() {
+                continue;
+            } else {
+                break parse(iter, c)?;
+            }
+        };
+
+        if values.contains_key(&key) {
+            return Err(format!("Duplicated key `{key}`"));
+        }
+        values.insert(key, value);
+
+        while let Some(c) = iter.next() {
+            if c.is_whitespace() {
+                continue;
+            } else if c == ',' {
+                break;
+            } else if c == '}' {
+                break 'main;
+            } else {
+                return Err(format!("Unexpected `{c}` when parsing array"));
+            }
+        }
+    }
+    Ok(JsonValue::Object(values))
+}
+
+fn parse<I: Iterator<Item = char>>(iter: &mut Peekable<I>, c: char) -> Result<JsonValue, String> {
+    match c {
+        '{' => parse_object(iter),
+        '"' => parse_string(iter),
+        '[' => parse_array(iter),
+        't' => parse_ident(iter, JsonValue::Bool(true), "true"),
+        'f' => parse_ident(iter, JsonValue::Bool(false), "false"),
+        'n' => parse_ident(iter, JsonValue::Null, "null"),
+        c => {
+            if c.is_ascii_digit() || c == '-' {
+                parse_number(iter, c)
+            } else {
+                Err(format!("Unexpected `{c}` character"))
+            }
+        }
+    }
+}
+
+impl JsonValue {
+    pub(crate) fn parse(input: &str) -> Result<Self, String> {
+        let mut iter = input.chars().peekable();
+        let mut value = None;
+
+        while let Some(c) = iter.next() {
+            if c.is_whitespace() {
+                continue;
+            }
+            value = Some(parse(&mut iter, c)?);
+            break;
+        }
+        while let Some(c) = iter.next() {
+            if c.is_whitespace() {
+                continue;
+            } else {
+                return Err(format!("Unexpected character `{c}` after content"));
+            }
+        }
+        if let Some(value) = value {
+            Ok(value)
+        } else {
+            Err("Empty content".to_string())
+        }
+    }
+}
diff --git a/scripts/rustdoc_test_builder.rs b/scripts/rustdoc_test_builder.rs
@@ -15,60 +15,100 @@
 //! from that. For the moment, we generate ourselves a new name, `{file}_{number}` instead, in
 //! the `gen` script (done there since we need to be aware of all the tests in a given file).
 
+use std::collections::HashMap;
 use std::io::Read;
+use std::fs::create_dir_all;
 
-fn main() {
-    let mut stdin = std::io::stdin().lock();
-    let mut body = String::new();
-    stdin.read_to_string(&mut body).unwrap();
+use json::JsonValue;
 
-    // Find the generated function name looking for the inner function inside `main()`.
-    //
-    // The line we are looking for looks like one of the following:
-    //
-    // ```
-    // 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> {
-    // ```
-    //
-    // It should be unlikely that doctest code matches such lines (when code is formatted properly).
-    let rustdoc_function_name = body
-        .lines()
-        .find_map(|line| {
-            Some(
-                line.split_once("fn main() {")?
-                    .1
-                    .split_once("fn ")?
-                    .1
-                    .split_once("()")?
-                    .0,
-            )
-            .filter(|x| x.chars().all(|c| c.is_alphanumeric() || c == '_'))
-        })
-        .expect("No test function found in `rustdoc`'s output.");
+mod json;
 
-    // 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> {{"
-        ),
-    );
+fn generate_doctest(file: &str, line: i32, doctest_code: &HashMap<String, JsonValue>) -> bool {
+    // FIXME: Once let chain feature is stable, please use it instead.
+    let Some(JsonValue::Object(wrapper)) = doctest_code.get("wrapper") else { return false };
+    let Some(JsonValue::String(before)) = wrapper.get("before") else { return false };
+    let Some(JsonValue::String(after)) = wrapper.get("after") else { return false };
+    let Some(JsonValue::String(code)) = doctest_code.get("code") else { return false };
+    let Some(JsonValue::String(crate_level_code)) = doctest_code.get("crate_level") else { return false };
 
-    // For tests that get generated with `Result`, like above, `rustdoc` generates an `unwrap()` on
+    // For tests that get generated with `Result`, `rustdoc` generates an `unwrap()` on
     // the return value to check there were no returned errors. Instead, we use our assert macro
     // since we want to just fail the test, not panic the kernel.
     //
     // 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()); }}"),
-    );
+    let after = if let Some(JsonValue::Bool(true)) = wrapper.get("returns_result") {
+        "\n} let test_return_value = _inner(); assert!(test_return_value.is_ok()); }"
+    } else {
+        after.as_str()
+    };
+    let code = format!("{crate_level_code}\n{before}\n{code}{after}\n");
+
+    let file = file
+        .strip_suffix(".rs")
+        .unwrap_or(file)
+        .strip_prefix("../rust/kernel/")
+        .unwrap_or(file)
+        .replace('/', "_");
+    let path = format!("rust/test/doctests/kernel/{file}-{line}.rs");
+
+    std::fs::write(path, code.as_bytes()).unwrap();
+    true
+}
+
+fn main() {
+    let mut stdin = std::io::stdin().lock();
+    let mut body = String::new();
+    stdin.read_to_string(&mut body).unwrap();
+
+    let JsonValue::Object(rustdoc) = JsonValue::parse(&body).unwrap() else {
+        panic!("Expected an object")
+    };
+    if let Some(JsonValue::Number(format_version)) = rustdoc.get("format_version") {
+        if *format_version != 2 {
+            panic!("unsupported rustdoc format version: {format_version}");
+        }
+    } else {
+        panic!("missing `format_version` field");
+    }
+    let Some(JsonValue::Array(doctests)) = rustdoc.get("doctests") else {
+        panic!("`doctests` field is missing or has the wrong type");
+    };
 
-    // Figure out a smaller test name based on the generated function name.
-    let name = rustdoc_function_name.split_once("_rust_kernel_").unwrap().1;
+    // We ignore the error since it will fail when generating doctests below if the folder doesn't
+    // exist.
+    let _ = create_dir_all("rust/test/doctests/kernel");
 
-    let path = format!("rust/test/doctests/kernel/{name}");
+    let mut nb_generated = 0;
+    for doctest in doctests {
+        let JsonValue::Object(doctest) = doctest else {
+            unreachable!()
+        };
+        // We check if we need to skip this test by checking it's a rust code and it's not ignored.
+        if let Some(JsonValue::Object(attributes)) = doctest.get("doctest_attributes") {
+            if attributes.get("rust") != Some(&JsonValue::Bool(true)) {
+                continue;
+            } else if let Some(JsonValue::String(ignore)) = attributes.get("ignore") {
+                if ignore != "None" {
+                    continue;
+                }
+            }
+        }
+        if let (
+            Some(JsonValue::String(file)),
+            Some(JsonValue::Number(line)),
+            Some(JsonValue::Object(doctest_code)),
+        ) = (
+            doctest.get("file"),
+            doctest.get("line"),
+            doctest.get("doctest_code"),
+        ) {
+            if generate_doctest(file, *line, doctest_code) {
+                nb_generated += 1;
+            }
+        }
+    }
 
-    std::fs::write(path, body.as_bytes()).unwrap();
+    if nb_generated == 0 {
+        panic!("No test function found in `rustdoc`'s output.");
+    }
 }
diff --git a/scripts/rustdoc_test_gen.rs b/scripts/rustdoc_test_gen.rs
