Avoid building rustdoc for tests without doctests

Author: chenyukang

src/bootstrap/src/core/builder/cargo.rs

@@ -918,7 +918,10 @@ impl Builder<'_> {
         }
 
         let rustdoc_path = match cmd_kind {
-            Kind::Doc | Kind::Test | Kind::MiriTest => self.rustdoc_for_compiler(compiler),
+            Kind::Doc => self.rustdoc_for_compiler(compiler),
+            Kind::Test | Kind::MiriTest if self.test_target.runs_doctests() => {
+                self.rustdoc_for_compiler(compiler)
+            }
             _ => PathBuf::from("/path/to/nowhere/rustdoc/not/required"),
         };
 

src/bootstrap/src/core/builder/tests.rs

@@ -2423,6 +2423,19 @@ mod snapshot {
         }
     }
 
+    #[test]
+    fn test_library_tests_only_does_not_build_rustdoc() {
+        let ctx = TestCtx::new();
+        let host = TargetSelection::from_user(&host_target());
+
+        let steps = ctx.config("test").args(&["--tests", "library/core"]).get_steps();
+
+        steps.assert_contains_fuzzy(StepMetadata::build("std", host));
+        steps.assert_no_match(|metadata| {
+            metadata.name == "rustdoc" && metadata.kind == Kind::Build && metadata.target == host
+        });
+    }
+
     #[test]
     fn test_cargo_stage_1() {
         let ctx = TestCtx::new();