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

Author: karolzwolak

compiler/rustc_span/src/symbol.rs

@@ -2510,12 +2510,24 @@ impl Ident {
         Ident::new(self.name, span.with_ctxt(self.span.ctxt()))
     }
 
-    /// 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.
+    /// Creates a new ident with the same span and name with leading quotes removed, if any.
+    /// If called on an empty ident, or with name just single quotes, returns an empty ident which is invalid.
+    /// Creating empty ident will trigger debug assertions.
+    /// Use `without_first_quote_checked` instead if not certain this will return valid ident.
     pub fn without_first_quote(self) -> Ident {
         Ident::new(Symbol::intern(self.as_str().trim_start_matches('\'')), self.span)
     }
 
+    /// Creates a new ident with the same span and name with leading quotes removed, if any.
+    /// If called on an empty ident, or with name just single quotes, returns `None`.
+    /// If you are certain this will return valid ident, use `without_first_quote` instead.
+    pub fn without_first_quote_checked(self) -> Option<Ident> {
+        match Symbol::intern(self.as_str().trim_start_matches('\'')) {
+            sym::empty => None,
+            name => Some(Ident::new(name, self.span)),
+        }
+    }
+
     /// "Normalize" ident for use in comparisons using "item hygiene".
     /// Identifiers with same string value become same if they came from the same macro 2.0 macro
     /// (e.g., `macro` item, but not `macro_rules` item) and stay different if they came from
@@ -3099,15 +3111,16 @@ impl Ident {
     }
 
     pub fn is_raw_lifetime_guess(self) -> bool {
-        // Check that the name isn't just a single quote.
+        // Ident name might be an empty string or just single quotes, so call checked function.
         // `self.without_first_quote()` would return empty ident, which triggers debug assert.
-        if self.name.as_str() == "'" {
-            return false;
+        match self.without_first_quote_checked() {
+            None => false,
+            Some(ident_without_apostrophe) => {
+                ident_without_apostrophe.name != self.name
+                    && ident_without_apostrophe.name.can_be_raw()
+                    && ident_without_apostrophe.is_reserved_lifetime()
+            }
         }
-        let ident_without_apostrophe = self.without_first_quote();
-        ident_without_apostrophe.name != self.name
-            && ident_without_apostrophe.name.can_be_raw()
-            && ident_without_apostrophe.is_reserved_lifetime()
     }
 
     pub fn guess_print_mode(self) -> IdentPrintMode {

tests/ui/extern/extern-single-quote-issue-147365.rs renamed to 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`.