Add regression test for #122722

Author: GuillaumeGomez

tests/run-make/rustdoc-test-args/Makefile

@@ -0,0 +1,10 @@
+include ../tools.mk
+
+# Test that rustdoc will properly load in a theme file and display it in the theme selector.
+
+OUTPUT_DIR := "$(TMPDIR)/rustdoc-test-args"
+
+all:
+	yes -- --cfg=A | head -n 100000 > cfgs
+	$(RUSTDOC) --test @cfgs foo.rs
+	rm cfgs

tests/run-make/rustdoc-test-args/foo.rs

@@ -0,0 +1,3 @@
+//! ```
+//! let x = 12;
+//! ```