3 files changed, 30 insertions, 0 deletions
diff --git a/src/test/run-make/incr-foreign-head-span/Makefile b/src/test/run-make/incr-foreign-head-span/Makefile
new file mode 100644
index 000000000..712965eaa
--- /dev/null
+++ b/src/test/run-make/incr-foreign-head-span/Makefile
@@ -0,0 +1,21 @@
+include ../../run-make-fulldeps/tools.mk
+
+# ignore-none no-std is not supported
+# ignore-nvptx64-nvidia-cuda FIXME: can't find crate for 'std'
+
+# Ensure that modifying a crate on disk (without recompiling it)
+# does not cause ICEs in downstream crates.
+# Previously, we would call `SourceMap.guess_head_span` on a span
+# from an external crate, which would cause us to read an upstream
+# source file from disk during compilation of a downstream crate
+# See #86480 for more details
+
+INCR=$(TMPDIR)/incr
+
+all:
+	cp first_crate.rs second_crate.rs $(TMPDIR)
+	$(RUSTC) $(TMPDIR)/first_crate.rs  -C incremental=$(INCR) --target $(TARGET) --crate-type lib
+	$(RUSTC) $(TMPDIR)/second_crate.rs -C incremental=$(INCR) --target $(TARGET)  --extern first-crate=$(TMPDIR) --crate-type lib
+	rm $(TMPDIR)/first_crate.rs
+	$(RUSTC) $(TMPDIR)/second_crate.rs  -C incremental=$(INCR) --target $(TARGET) --cfg second_run --crate-type lib
+
diff --git a/src/test/run-make/incr-foreign-head-span/first_crate.rs b/src/test/run-make/incr-foreign-head-span/first_crate.rs
new file mode 100644
index 000000000..69dd103bf
--- /dev/null
+++ b/src/test/run-make/incr-foreign-head-span/first_crate.rs
@@ -0,0 +1 @@
+pub trait OtherTrait {}
diff --git a/src/test/run-make/incr-foreign-head-span/second_crate.rs b/src/test/run-make/incr-foreign-head-span/second_crate.rs
new file mode 100644
index 000000000..102f6b26c
--- /dev/null
+++ b/src/test/run-make/incr-foreign-head-span/second_crate.rs
@@ -0,0 +1,8 @@
+extern crate first_crate;
+use first_crate::OtherTrait;
+
+#[cfg(not(second_run))]
+trait Foo: OtherTrait {}
+
+#[cfg(second_run)]
+trait Bar: OtherTrait {}