don't panic on extern with just multiple quotes in the name

compiler/rustc_span/src/symbol.rs

@@ -2511,9 +2511,11 @@ impl Ident {
     }
 
     /// Creates a new ident with the same span and name with leading quote removed, if any.
-    /// If called on an empty ident, or with name just a single quote, returns an empty ident which is invalid.
+    /// Calling it on a `'` ident will return an empty ident, which triggers debug assertions.
     pub fn without_first_quote(self) -> Ident {
-        Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
+        self.as_str()
+            .strip_prefix('\'')
+            .map_or(self, |name| Ident::new(Symbol::intern(name), self.span))
     }
 
     /// "Normalize" ident for use in comparisons using "item hygiene".

tests/ui/extern/extern-only-quotes-issue-147365.rs

@@ -2,8 +2,12 @@
 
 // https://github.com/rust-lang/rust/issues/147365
 // Ensures we don't trigger debug assert by creating an empty Ident when determining whether
-// the single quote is a raw lifetime.
+// the quotes are a raw lifetime.
 
 extern "'" {} //~ ERROR invalid ABI: found `'`
 
+extern "''" {} //~ ERROR invalid ABI: found `''`
+
+extern "'''" {} //~ ERROR invalid ABI: found `'''`
+
 fn main() {}

tests/ui/extern/extern-only-quotes-issue-147365.stderr

@@ -0,0 +1,32 @@
+error[E0703]: invalid ABI: found `'`
+  --> $DIR/extern-only-quotes-issue-147365.rs:7:8
+   |
+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 "'" {}
+LL + extern "C" {}
+   |
+
+error[E0703]: invalid ABI: found `''`
+  --> $DIR/extern-only-quotes-issue-147365.rs:9:8
+   |
+LL | extern "''" {}
+   |        ^^^^ invalid ABI
+   |
+   = note: invoke `rustc --print=calling-conventions` for a full list of supported calling conventions
+
+error[E0703]: invalid ABI: found `'''`
+  --> $DIR/extern-only-quotes-issue-147365.rs:11:8
+   |
+LL | extern "'''" {}
+   |        ^^^^^ invalid ABI
+   |
+   = note: invoke `rustc --print=calling-conventions` for a full list of supported calling conventions
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0703`.

tests/ui/extern/extern-single-quote-issue-147365.stderr

@@ -1,16 +0,0 @@
-error[E0703]: invalid ABI: found `'`
-  --> $DIR/extern-single-quote-issue-147365.rs:7:8
-   |
-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 "'" {}
-LL + extern "C" {}
-   |
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0703`.