Add regression test for rustdoc scrape-examples feature crash (#144752)

tests/run-make/rustdoc-scrape-examples-paths/foo/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "foo"
+version = "0.0.1"
+edition = "2024"
+
+[[example]]
+name = "complex"
+doc-scrape-examples = true

tests/run-make/rustdoc-scrape-examples-paths/foo/examples/complex.rs

@@ -0,0 +1,3 @@
+fn main() {
+    let mut x = foo::X::new();
+}

tests/run-make/rustdoc-scrape-examples-paths/foo/examples/tester.rs

@@ -0,0 +1 @@
+// This file MUST exist to trigger the original bug.

tests/run-make/rustdoc-scrape-examples-paths/foo/src/lib.rs

@@ -0,0 +1,7 @@
+pub struct X;
+
+impl X {
+    pub fn new() -> Self {
+        X
+    }
+}

tests/run-make/rustdoc-scrape-examples-paths/rmake.rs

@@ -0,0 +1,16 @@
+//! Test to ensure that the rustdoc `scrape-examples` feature is not panicking.
+//! Regression test for <https://github.com/rust-lang/rust/issues/144752>.
+
+use run_make_support::{cargo, path, rfs};
+
+fn main() {
+    // We copy the crate to be documented "outside" to prevent documenting
+    // the whole compiler.
+    let tmp = std::env::temp_dir();
+    let test_crate = tmp.join("foo");
+    rfs::copy_dir_all(path("foo"), &test_crate);
+
+    // The `scrape-examples` feature is also implemented in `cargo` so instead of reproducing
+    // what `cargo` does, better to just let `cargo` do it.
+    cargo().current_dir(&test_crate).args(["doc", "-p", "foo", "-Zrustdoc-scrape-examples"]).run();
+}