Rollup merge of #155485 - Urgau:remap-edge-case-test, r=GuillaumeGomez

Add an edge-case test for `--remap-path-prefix` for `rustc` & `rustdoc`

Intended to resolve @lolbinarycat concern https://github.com/rust-lang/rust/pull/155307#issuecomment-4270904667

tests/run-make/remap-path-prefix-edge-cases/rmake.rs

@@ -0,0 +1,51 @@
+//! This test checks multiple edge-case of `--remap-path-prefix`.
+//!
+//! It tests:
+//!  - `=` sign in FROM path
+//!  - multiple path remappings
+//!  - multiple conflicting path remappings
+
+//@ ignore-windows (does not support directories with = sign)
+
+use std::path::Path;
+
+use run_make_support::{
+    CompletedProcess, assert_contains, assert_not_contains, cwd, rfs, run_in_tmpdir, rustc, rustdoc,
+};
+
+fn main() {
+    run_in_tmpdir(|| {
+        let out_dir = cwd();
+
+        // Create a directory with an `=` sign
+        let eq_dir = out_dir.join("path=with=equal");
+        rfs::create_dir_all(&eq_dir);
+
+        let src_path = eq_dir.join("lib.rs");
+        rfs::write(&src_path, "pub fn broken_func() { ");
+
+        // Use multiple remap args and conflicting remappings
+        let remap_args = [
+            format!("--remap-path-prefix={}={}", eq_dir.display(), "REMAPPED_DIR"),
+            format!("--remap-path-prefix={}={}", eq_dir.display(), "REMAPPED_DIR2"),
+        ];
+
+        fn run_test(cmd: impl FnOnce() -> CompletedProcess) {
+            let output = cmd();
+            let stderr = output.stderr_utf8();
+
+            // Checks the diagnostic output
+            assert_contains(&stderr, "REMAPPED_DIR2/lib.rs");
+            assert_not_contains(&stderr, "REMAPPED_DIR/");
+            assert_not_contains(&stderr, "path=with=equal");
+        };
+
+        // Test with rustc
+        run_test(|| rustc().input(&src_path).args(&remap_args).run_fail());
+
+        // Test with rustdoc
+        run_test(|| {
+            rustdoc().input(&src_path).arg("-Zunstable-options").args(&remap_args).run_fail()
+        });
+    });
+}