Rollup merge of #141318 - nnethercote:fix-140884, r=compiler-errors

Avoid creating an empty identifer in `Symbol::to_ident_string`.

Because that causes an assertion failure in debug builds.

Fixes #140884.

r? `@oli-obk`

3 files changed, 18 insertions, 6 deletions

diff --git a/tests/crashes/140884.rs b/tests/crashes/140884.rs
deleted file mode 100644
index 6840760933a..00000000000
--- a/tests/crashes/140884.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-//@ known-bug: #140884
-//@ needs-rustc-debug-assertions
-
-fn a() {
-    extern "" {}
-}
diff --git a/tests/ui/extern/extern-empty-string-issue-140884.rs b/tests/ui/extern/extern-empty-string-issue-140884.rs
new file mode 100644
index 00000000000..10291513d34
--- /dev/null
+++ b/tests/ui/extern/extern-empty-string-issue-140884.rs
@@ -0,0 +1,3 @@
+extern "" {} //~ ERROR invalid ABI: found ``
+
+fn main() {}
diff --git a/tests/ui/extern/extern-empty-string-issue-140884.stderr b/tests/ui/extern/extern-empty-string-issue-140884.stderr
new file mode 100644
index 00000000000..accae0c0f7c
--- /dev/null
+++ b/tests/ui/extern/extern-empty-string-issue-140884.stderr
@@ -0,0 +1,15 @@
+error[E0703]: invalid ABI: found ``
+  --> $DIR/extern-empty-string-issue-140884.rs:1:8
+   |
+LL | extern "" {}
+   |        ^^ invalid ABI
+   |
+   = note: invoke `rustc --print=calling-conventions` for a full list of supported calling conventions
+help: there's a similarly named valid ABI `C`
+   |
+LL | extern "C" {}
+   |         +
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0703`.