[rustdoc] Add --extract-doctests command-line flag

src/doc/rustdoc/src/unstable-features.md

@@ -664,3 +664,22 @@ Similar to cargo `build.rustc-wrapper` option, this flag takes a `rustc` wrapper
 The first argument to the program will be the test builder program.
 
 This flag can be passed multiple times to nest wrappers.
+
+### `--extract-doctests`: outputs doctests in JSON format
+
+ * Tracking issue: [#134529](https://github.com/rust-lang/rust/issues/134529)
+
+When this flag is used, it outputs the doctests original source code alongside information
+such as:
+
+ * File where they are located.
+ * Line where they are located.
+ * Codeblock attributes (more information about this [here](./write-documentation/documentation-tests.html#attributes)).
+
+The output format is JSON.
+
+Using this flag looks like this:
+
+```bash
+$ rustdoc -Zunstable-options --extract-doctests src/lib.rs
+```

src/librustdoc/config.rs

@@ -172,6 +172,9 @@ pub(crate) struct Options {
     /// This is mainly useful for other tools that reads that debuginfo to figure out
     /// how to call the compiler with the same arguments.
     pub(crate) expanded_args: Vec<String>,
+
+    /// If `true`, it will doctest in JSON format and exit.
+    pub(crate) extract_doctests: bool,
 }
 
 impl fmt::Debug for Options {
@@ -762,6 +765,7 @@ impl Options {
             Ok(result) => result,
             Err(e) => dcx.fatal(format!("--merge option error: {e}")),
         };
+        let extract_doctests = matches.opt_present("extract-doctests");
 
         if generate_link_to_definition && (show_coverage || output_format != OutputFormat::Html) {
             dcx.struct_warn(
@@ -819,6 +823,7 @@ impl Options {
             scrape_examples_options,
             unstable_features,
             expanded_args: args,
+            extract_doctests,
         };
         let render_options = RenderOptions {
             output,

src/librustdoc/doctest.rs

@@ -26,6 +26,7 @@ use rustc_span::FileName;
 use rustc_span::edition::Edition;
 use rustc_span::symbol::sym;
 use rustc_target::spec::{Target, TargetTuple};
+use serde::ser::{Serialize, SerializeStruct, Serializer};
 use tempfile::{Builder as TempFileBuilder, TempDir};
 use tracing::debug;
 
@@ -165,6 +166,7 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
     let args_path = temp_dir.path().join("rustdoc-cfgs");
     crate::wrap_return(dcx, generate_args_file(&args_path, &options));
 
+    let extract_doctests = options.extract_doctests;
     let CreateRunnableDocTests {
         standalone_tests,
         mergeable_tests,
@@ -173,7 +175,7 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
         unused_extern_reports,
         compiling_test_count,
         ..
-    } = interface::run_compiler(config, |compiler| {
+    } = match interface::run_compiler(config, |compiler| {
         let krate = rustc_interface::passes::parse(&compiler.sess);
 
         let collector = rustc_interface::create_and_enter_global_ctxt(&compiler, krate, |tcx| {
@@ -189,14 +191,30 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
                 tcx,
             );
             let tests = hir_collector.collect_crate();
+            if extract_doctests {
+                let stdout = std::io::stdout();
+                let mut stdout = stdout.lock();
+                if let Err(error) = serde_json::ser::to_writer(&mut stdout, &tests) {
+                    eprintln!();
+                    return Err(format!("Failed to generate JSON output for doctests: {error:?}"));
+                }
+                return Ok(None);
+            }
             tests.into_iter().for_each(|t| collector.add_test(t));
 
-            collector
+            Ok(Some(collector))
         });
         compiler.sess.dcx().abort_if_errors();
 
         collector
-    });
+    }) {
+        Ok(Some(collector)) => collector,
+        Ok(None) => return,
+        Err(error) => {
+            eprintln!("{error}");
+            std::process::exit(1);
+        }
+    };
 
     run_tests(opts, &rustdoc_options, &unused_extern_reports, standalone_tests, mergeable_tests);
 
@@ -725,6 +743,25 @@ pub(crate) struct ScrapedDocTest {
     name: String,
 }
 
+// This implementation is needed for 2 reasons:
+// 1. `FileName` doesn't implement `serde::Serialize`.
+// 2. We don't want to output `name`.
+impl Serialize for ScrapedDocTest {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        // `5` is the number of fields we output (so all of them except `name`).
+        let mut s = serializer.serialize_struct("ScrapedDocTest", 4)?;
+        let filename = self.filename.prefer_remapped_unconditionaly().to_string();
+        s.serialize_field("filename", &filename)?;
+        s.serialize_field("line", &self.line)?;
+        s.serialize_field("langstr", &self.langstr)?;
+        s.serialize_field("text", &self.text)?;
+        s.end()
+    }
+}
+
 impl ScrapedDocTest {
     fn new(
         filename: FileName,

src/librustdoc/html/markdown.rs

@@ -46,6 +46,7 @@ pub(crate) use rustc_resolve::rustdoc::main_body_opts;
 use rustc_resolve::rustdoc::may_be_doc_link;
 use rustc_span::edition::Edition;
 use rustc_span::{Span, Symbol};
+use serde::ser::{Serialize, SerializeStruct, Serializer};
 use tracing::{debug, trace};
 
 use crate::clean::RenderedLink;
@@ -836,7 +837,35 @@ pub(crate) struct LangString {
     pub(crate) unknown: Vec<String>,
 }
 
-#[derive(Eq, PartialEq, Clone, Debug)]
+// This implementation is needed for `Edition` which doesn't implement `serde::Serialize` so
+// we need to implement it manually.
+impl Serialize for LangString {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        // `12` is the number of fields.
+        let mut s = serializer.serialize_struct("LangString", 12)?;
+
+        s.serialize_field("original", &self.original)?;
+        s.serialize_field("should_panic", &self.should_panic)?;
+        s.serialize_field("no_run", &self.no_run)?;
+        s.serialize_field("ignore", &self.ignore)?;
+        s.serialize_field("rust", &self.rust)?;
+        s.serialize_field("test_harness", &self.test_harness)?;
+        s.serialize_field("compile_fail", &self.compile_fail)?;
+        s.serialize_field("standalone_crate", &self.standalone_crate)?;
+        s.serialize_field("error_codes", &self.error_codes)?;
+        let edition = self.edition.map(|edition| edition.to_string());
+        s.serialize_field("edition", &edition)?;
+        s.serialize_field("added_classes", &self.added_classes)?;
+        s.serialize_field("unknown", &self.unknown)?;
+
+        s.end()
+    }
+}
+
+#[derive(Eq, PartialEq, Clone, Debug, serde::Serialize)]
 pub(crate) enum Ignore {
     All,
     None,

src/librustdoc/lib.rs

@@ -685,6 +685,7 @@ fn opts() -> Vec<RustcOptGroup> {
             "[rust]",
         ),
         opt(Unstable, Flag, "", "html-no-source", "Disable HTML source code pages generation", ""),
+        opt(Unstable, Flag, "", "extract-doctests", "Output doctests in JSON format", ""),
     ]
 }
 
@@ -804,7 +805,7 @@ fn main_args(
         }
     };
 
-    match (options.should_test, config::markdown_input(&input)) {
+    match (options.should_test | options.extract_doctests, config::markdown_input(&input)) {
         (true, Some(_)) => return wrap_return(dcx, doctest::test_markdown(&input, options)),
         (true, None) => return doctest::run(dcx, input, options),
         (false, Some(md_input)) => {

tests/rustdoc-ui/extract-doctests.rs

@@ -0,0 +1,14 @@
+// Test to ensure that it generates expected output for `--extract-doctests` command-line
+// flag.
+
+//@ compile-flags:-Z unstable-options --extract-doctests
+//@ check-pass
+
+//! ```ignore (checking attributes)
+//! let x = 12;
+//! let y = 14;
+//! ```
+//!
+//! ```edition2018,compile_fail
+//! let
+//! ```

tests/rustdoc-ui/extract-doctests.stdout

@@ -0,0 +1 @@
+[{"filename":"tests/rustdoc-ui/extract-doctests.rs","line":7,"langstr":{"original":"ignore (checking attributes)","should_panic":false,"no_run":false,"ignore":"All","rust":true,"test_harness":false,"compile_fail":false,"standalone_crate":false,"error_codes":[],"edition":null,"added_classes":[],"unknown":[]},"text":"let x = 12;\nlet y = 14;"},{"filename":"tests/rustdoc-ui/extract-doctests.rs","line":12,"langstr":{"original":"edition2018,compile_fail","should_panic":false,"no_run":true,"ignore":"None","rust":true,"test_harness":false,"compile_fail":true,"standalone_crate":false,"error_codes":[],"edition":"2018","added_classes":[],"unknown":[]},"text":"let"}]