Add new failed_merged_doctest_compilation rustdoc lint

src/librustdoc/doctest.rs

@@ -23,6 +23,7 @@ use rustc_hir as hir;
 use rustc_hir::CRATE_HIR_ID;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_interface::interface;
+use rustc_middle::ty::TyCtxt;
 use rustc_session::config::{self, CrateType, ErrorOutputType, Input};
 use rustc_session::lint;
 use rustc_span::edition::Edition;
@@ -204,13 +205,14 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
         Err(error) => return crate::wrap_return(dcx, Err(error)),
     };
     let args_path = temp_dir.path().join("rustdoc-cfgs");
+    let temp_dir_path = temp_dir.path().to_path_buf();
     crate::wrap_return(dcx, generate_args_file(&args_path, &options));
 
     let extract_doctests = options.output_format == OutputFormat::Doctest;
     let result = 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| {
+        rustc_interface::create_and_enter_global_ctxt(compiler, krate, |tcx| {
             let crate_name = tcx.crate_name(LOCAL_CRATE).to_string();
             let crate_attrs = tcx.hir_attrs(CRATE_HIR_ID);
             let opts = scrape_test_config(crate_name, crate_attrs, args_path);
@@ -220,6 +222,8 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
                 tcx,
             );
             let tests = hir_collector.collect_crate();
+            tcx.dcx().abort_if_errors();
+
             if extract_doctests {
                 let mut collector = extracted::ExtractedDocTests::new();
                 tests.into_iter().for_each(|t| collector.add_test(t, &opts, &options));
@@ -228,90 +232,87 @@ pub(crate) fn run(dcx: DiagCtxtHandle<'_>, input: Input, options: RustdocOptions
                 let mut stdout = stdout.lock();
                 if let Err(error) = serde_json::ser::to_writer(&mut stdout, &collector) {
                     eprintln!();
-                    Err(format!("Failed to generate JSON output for doctests: {error:?}"))
+                    return Err(format!("Failed to generate JSON output for doctests: {error:?}"));
                 } else {
-                    Ok(None)
+                    return Ok(());
                 }
-            } else {
-                let mut collector = CreateRunnableDocTests::new(options, opts);
-                tests.into_iter().for_each(|t| collector.add_test(t, Some(compiler.sess.dcx())));
-
-                Ok(Some(collector))
             }
-        });
-        compiler.sess.dcx().abort_if_errors();
+            let mut collector = CreateRunnableDocTests::new(options, opts);
+            tests.into_iter().for_each(|t| collector.add_test(t, Some(compiler.sess.dcx())));
 
-        collector
-    });
+            let CreateRunnableDocTests {
+                standalone_tests,
+                mergeable_tests,
+                rustdoc_options,
+                opts,
+                unused_extern_reports,
+                compiling_test_count,
+                ..
+            } = collector;
 
-    let CreateRunnableDocTests {
-        standalone_tests,
-        mergeable_tests,
-        rustdoc_options,
-        opts,
-        unused_extern_reports,
-        compiling_test_count,
-        ..
-    } = match result {
-        Ok(Some(collector)) => collector,
-        Ok(None) => return,
-        Err(error) => {
-            eprintln!("{error}");
-            // Since some files in the temporary folder are still owned and alive, we need
-            // to manually remove the folder.
-            let _ = std::fs::remove_dir_all(temp_dir.path());
-            std::process::exit(1);
-        }
-    };
+            run_tests(
+                opts,
+                &rustdoc_options,
+                &unused_extern_reports,
+                standalone_tests,
+                mergeable_tests,
+                Some(temp_dir),
+                Some(tcx),
+            );
 
-    run_tests(
-        opts,
-        &rustdoc_options,
-        &unused_extern_reports,
-        standalone_tests,
-        mergeable_tests,
-        Some(temp_dir),
-    );
+            let compiling_test_count = compiling_test_count.load(Ordering::SeqCst);
+
+            // Collect and warn about unused externs, but only if we've gotten
+            // reports for each doctest
+            if json_unused_externs.is_enabled() {
+                let unused_extern_reports: Vec<_> =
+                    std::mem::take(&mut unused_extern_reports.lock().unwrap());
+                if unused_extern_reports.len() == compiling_test_count {
+                    let extern_names =
+                        externs.iter().map(|(name, _)| name).collect::<FxIndexSet<&String>>();
+                    let mut unused_extern_names = unused_extern_reports
+                        .iter()
+                        .map(|uexts| {
+                            uexts.unused_extern_names.iter().collect::<FxIndexSet<&String>>()
+                        })
+                        .fold(extern_names, |uextsa, uextsb| {
+                            uextsa.intersection(&uextsb).copied().collect::<FxIndexSet<&String>>()
+                        })
+                        .iter()
+                        .map(|v| (*v).clone())
+                        .collect::<Vec<String>>();
+                    unused_extern_names.sort();
+                    // Take the most severe lint level
+                    let lint_level = unused_extern_reports
+                        .iter()
+                        .map(|uexts| uexts.lint_level.as_str())
+                        .max_by_key(|v| match *v {
+                            "warn" => 1,
+                            "deny" => 2,
+                            "forbid" => 3,
+                            // The allow lint level is not expected,
+                            // as if allow is specified, no message
+                            // is to be emitted.
+                            v => unreachable!("Invalid lint level '{v}'"),
+                        })
+                        .unwrap_or("warn")
+                        .to_string();
+                    let uext = UnusedExterns { lint_level, unused_extern_names };
+                    let unused_extern_json = serde_json::to_string(&uext).unwrap();
+                    eprintln!("{unused_extern_json}");
+                }
+            }
 
-    let compiling_test_count = compiling_test_count.load(Ordering::SeqCst);
-
-    // Collect and warn about unused externs, but only if we've gotten
-    // reports for each doctest
-    if json_unused_externs.is_enabled() {
-        let unused_extern_reports: Vec<_> =
-            std::mem::take(&mut unused_extern_reports.lock().unwrap());
-        if unused_extern_reports.len() == compiling_test_count {
-            let extern_names =
-                externs.iter().map(|(name, _)| name).collect::<FxIndexSet<&String>>();
-            let mut unused_extern_names = unused_extern_reports
-                .iter()
-                .map(|uexts| uexts.unused_extern_names.iter().collect::<FxIndexSet<&String>>())
-                .fold(extern_names, |uextsa, uextsb| {
-                    uextsa.intersection(&uextsb).copied().collect::<FxIndexSet<&String>>()
-                })
-                .iter()
-                .map(|v| (*v).clone())
-                .collect::<Vec<String>>();
-            unused_extern_names.sort();
-            // Take the most severe lint level
-            let lint_level = unused_extern_reports
-                .iter()
-                .map(|uexts| uexts.lint_level.as_str())
-                .max_by_key(|v| match *v {
-                    "warn" => 1,
-                    "deny" => 2,
-                    "forbid" => 3,
-                    // The allow lint level is not expected,
-                    // as if allow is specified, no message
-                    // is to be emitted.
-                    v => unreachable!("Invalid lint level '{v}'"),
-                })
-                .unwrap_or("warn")
-                .to_string();
-            let uext = UnusedExterns { lint_level, unused_extern_names };
-            let unused_extern_json = serde_json::to_string(&uext).unwrap();
-            eprintln!("{unused_extern_json}");
-        }
+            Ok(())
+        })
+    });
+
+    if let Err(error) = result {
+        eprintln!("{error}");
+        // Since some files in the temporary folder are still owned and alive, we need
+        // to manually remove the folder.
+        let _ = std::fs::remove_dir_all(temp_dir_path);
+        std::process::exit(1);
     }
 }
 
@@ -323,6 +324,7 @@ pub(crate) fn run_tests(
     mergeable_tests: FxIndexMap<MergeableTestKey, Vec<(DocTestBuilder, ScrapedDocTest)>>,
     // We pass this argument so we can drop it manually before using `exit`.
     mut temp_dir: Option<TempDir>,
+    tcx: Option<TyCtxt<'_>>,
 ) {
     let mut test_args = Vec::with_capacity(rustdoc_options.test_args.len() + 1);
     test_args.insert(0, "rustdoctest".to_string());
@@ -368,6 +370,18 @@ pub(crate) fn run_tests(
             }
             continue;
         }
+        if let Some(tcx) = tcx {
+            tcx.node_span_lint(
+                crate::lint::FAILED_MERGED_DOCTEST_COMPILATION,
+                CRATE_HIR_ID,
+                tcx.hir_span(CRATE_HIR_ID),
+                |lint| {
+                    lint.primary_message(
+                        format!("failed to compile merged doctests for edition {edition}. Reverting to standalone doctests."),
+                    );
+                },
+            );
+        }
         // We failed to compile all compatible tests as one so we push them into the
         // `standalone_tests` doctests.
         debug!("Failed to compile compatible doctests for edition {} all at once", edition);

src/librustdoc/doctest/markdown.rs

@@ -124,6 +124,7 @@ pub(crate) fn test(input: &Input, options: Options) -> Result<(), String> {
         standalone_tests,
         mergeable_tests,
         None,
+        None,
     );
     Ok(())
 }

src/librustdoc/lint.rs

@@ -196,6 +196,17 @@ declare_rustdoc_lint! {
     "detects redundant explicit links in doc comments"
 }
 
+declare_rustdoc_lint! {
+    /// This lint is **warn-by-default**. It warns when merged doctests fail to compile
+    /// when running doctests. This is a `rustdoc` only lint, see the documentation in
+    /// the [rustdoc book].
+    ///
+    /// [rustdoc book]: ../../../rustdoc/lints.html#failed_merged_doctest_compilation
+    FAILED_MERGED_DOCTEST_COMPILATION,
+    Warn,
+    "warns when merged doctest fail to compile when running doctests"
+}
+
 pub(crate) static RUSTDOC_LINTS: Lazy<Vec<&'static Lint>> = Lazy::new(|| {
     vec![
         BROKEN_INTRA_DOC_LINKS,
@@ -209,6 +220,7 @@ pub(crate) static RUSTDOC_LINTS: Lazy<Vec<&'static Lint>> = Lazy::new(|| {
         MISSING_CRATE_LEVEL_DOCS,
         UNESCAPED_BACKTICKS,
         REDUNDANT_EXPLICIT_LINKS,
+        FAILED_MERGED_DOCTEST_COMPILATION,
     ]
 });
 

tests/rustdoc-ui/doctest/dead-code-2024.rs

@@ -8,6 +8,7 @@
 //@ normalize-stdout: "compilation took \d+\.\d+s" -> "compilation took $$TIME"
 //@ failure-status: 101
 
+#![allow(rustdoc::failed_merged_doctest_compilation)]
 #![doc(test(attr(allow(unused_variables), deny(warnings))))]
 
 /// Example

tests/rustdoc-ui/doctest/dead-code-2024.stdout

@@ -1,18 +1,18 @@
 
 running 1 test
-test $DIR/dead-code-2024.rs - f (line 15) - compile ... FAILED
+test $DIR/dead-code-2024.rs - f (line 16) - compile ... FAILED
 
 failures:
 
----- $DIR/dead-code-2024.rs - f (line 15) stdout ----
+---- $DIR/dead-code-2024.rs - f (line 16) stdout ----
 error: trait `T` is never used
-  --> $DIR/dead-code-2024.rs:16:7
+  --> $DIR/dead-code-2024.rs:17:7
    |
 LL | trait T { fn f(); }
    |       ^
    |
 note: the lint level is defined here
-  --> $DIR/dead-code-2024.rs:14:9
+  --> $DIR/dead-code-2024.rs:15:9
    |
 LL | #![deny(warnings)]
    |         ^^^^^^^^
@@ -23,7 +23,7 @@ error: aborting due to 1 previous error
 Couldn't compile the test.
 
 failures:
-    $DIR/dead-code-2024.rs - f (line 15)
+    $DIR/dead-code-2024.rs - f (line 16)
 
 test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
 

tests/rustdoc-ui/doctest/dead-code-items.rs

@@ -9,6 +9,7 @@
 //@ failure-status: 101
 
 #![doc(test(attr(deny(warnings))))]
+#![allow(rustdoc::failed_merged_doctest_compilation)]
 
 #[doc(test(attr(allow(dead_code))))]
 /// Example