error on empty precision

Author: hkBst

compiler/rustc_parse_format/src/lib.rs

@@ -696,8 +696,16 @@ impl<'a> Parser<'a> {
             } else {
                 spec.precision = self.count(start + 1);
             }
-            let end = self.current_pos();
-            spec.precision_span = Some(self.span(start, end));
+            if spec.precision == CountImplied {
+                self.err(
+                    "expected numerical precision",
+                    "missing precision",
+                    self.span(start, end),
+                );
+            } else {
+                let end = self.current_pos();
+                spec.precision_span = Some(self.span(start, end));
+            }
         }
 
         let ty_span_start = self.current_pos();