Auto merge of #32169 - mitaa:anon-tip, r=nrc

Allow custom filenames for anonymous inputs

This came out of #29253 but doesn't fix it.

I thought it might be worth merging on its own nonetheless.

src/librustdoc/test.rs

@@ -180,7 +180,10 @@ fn runtest(test: &str, cratename: &str, cfgs: Vec<String>, libs: SearchPaths,
     // the test harness wants its own `main` & top level functions, so
     // never wrap the test in `fn main() { ... }`
     let test = maketest(test, Some(cratename), as_test_harness, opts);
-    let input = config::Input::Str(test.to_string());
+    let input = config::Input::Str {
+        name: driver::anon_src(),
+        input: test.to_owned(),
+    };
     let mut outputs = HashMap::new();
     outputs.insert(OutputType::Exe, None);