Rollup merge of rust-lang#138281 - saethlin:mergeable-doctests-stacksize, r=GuillaumeGomez

Fix O(tests) stack usage in edition 2024 mergeable doctests

Fixes rust-lang#138248

The important change here is that we are not passing a potentially-large array by value. Between the fact that `TestFn` cannot be `Clone` and `test_main` takes a `Vec<TestDescAndFn>`, the only way to call `test::test_main` without O(tests) stack use is to call `Vec::push` many times.

The normal test harness does not have this problem because it calls `test_main_static` or `test_main_static_abort`, which take `&[TestDescAndFn]`. Changing `test::test_main` to take a slice is not a simple change, so I'm avoiding doing it here.

Author: matthiaskrgr

src/librustdoc/doctest/runner.rs

@@ -47,11 +47,8 @@ impl DocTestRunner {
                 self.crate_attrs.insert(line.to_string());
             }
         }
-        if !self.ids.is_empty() {
-            self.ids.push(',');
-        }
         self.ids.push_str(&format!(
-            "{}::TEST",
+            "tests.push({}::TEST);\n",
             generate_mergeable_doctest(
                 doctest,
                 scraped_test,
@@ -142,19 +139,23 @@ mod __doctest_mod {{
 
 #[rustc_main]
 fn main() -> std::process::ExitCode {{
-const TESTS: [test::TestDescAndFn; {nb_tests}] = [{ids}];
+let tests = {{
+    let mut tests = Vec::with_capacity({nb_tests});
+    {ids}
+    tests
+}};
 let test_marker = std::ffi::OsStr::new(__doctest_mod::RUN_OPTION);
 let test_args = &[{test_args}];
 const ENV_BIN: &'static str = \"RUSTDOC_DOCTEST_BIN_PATH\";
 
 if let Ok(binary) = std::env::var(ENV_BIN) {{
     let _ = crate::__doctest_mod::BINARY_PATH.set(binary.into());
     unsafe {{ std::env::remove_var(ENV_BIN); }}
-    return std::process::Termination::report(test::test_main(test_args, Vec::from(TESTS), None));
+    return std::process::Termination::report(test::test_main(test_args, tests, None));
 }} else if let Ok(nb_test) = std::env::var(__doctest_mod::RUN_OPTION) {{
     if let Ok(nb_test) = nb_test.parse::<usize>() {{
-        if let Some(test) = TESTS.get(nb_test) {{
-            if let test::StaticTestFn(f) = test.testfn {{
+        if let Some(test) = tests.get(nb_test) {{
+            if let test::StaticTestFn(f) = &test.testfn {{
                 return std::process::Termination::report(f());
             }}
         }}
@@ -164,7 +165,7 @@ if let Ok(binary) = std::env::var(ENV_BIN) {{
 
 eprintln!(\"WARNING: No rustdoc doctest environment variable provided so doctests will be run in \
 the same process\");
-std::process::Termination::report(test::test_main(test_args, Vec::from(TESTS), None))
+std::process::Termination::report(test::test_main(test_args, tests, None))
 }}",
             nb_tests = self.nb_tests,
             output = self.output_merged_tests,