Merge pull request rust-lang#20886 from A4-Tacks/parse-missing-method-name

Improve parsing of missing name in MethodCallExpr

Author: Veykril

src/tools/rust-analyzer/crates/parser/src/grammar/expressions.rs

@@ -430,6 +430,11 @@ fn postfix_expr(
             // }
             T!['('] if allow_calls => call_expr(p, lhs),
             T!['['] if allow_calls => index_expr(p, lhs),
+            // test_err postfix_dot_expr_ambiguity
+            // fn foo() {
+            //     x.
+            //     ()
+            // }
             T![.] => match postfix_dot_expr::<false>(p, lhs) {
                 Ok(it) => it,
                 Err(it) => {
@@ -458,6 +463,7 @@ fn postfix_dot_expr<const FLOAT_RECOVERY: bool>(
 
     if PATH_NAME_REF_KINDS.contains(p.nth(nth1))
         && (p.nth(nth2) == T!['('] || p.nth_at(nth2, T![::]))
+        || p.nth(nth1) == T!['(']
     {
         return Ok(method_call_expr::<FLOAT_RECOVERY>(p, lhs));
     }
@@ -526,19 +532,26 @@ fn method_call_expr<const FLOAT_RECOVERY: bool>(
     lhs: CompletedMarker,
 ) -> CompletedMarker {
     if FLOAT_RECOVERY {
-        assert!(p.at_ts(PATH_NAME_REF_KINDS) && (p.nth(1) == T!['('] || p.nth_at(1, T![::])));
+        assert!(
+            p.at_ts(PATH_NAME_REF_KINDS) && (p.nth(1) == T!['('] || p.nth_at(1, T![::]))
+                || p.current() == T!['(']
+        );
     } else {
+        assert!(p.at(T![.]));
         assert!(
-            p.at(T![.])
-                && PATH_NAME_REF_KINDS.contains(p.nth(1))
-                && (p.nth(2) == T!['('] || p.nth_at(2, T![::]))
+            PATH_NAME_REF_KINDS.contains(p.nth(1)) && (p.nth(2) == T!['('] || p.nth_at(2, T![::]))
+                || p.nth(1) == T!['(']
         );
     }
     let m = lhs.precede(p);
     if !FLOAT_RECOVERY {
         p.bump(T![.]);
     }
-    name_ref_mod_path(p);
+    if p.at_ts(PATH_NAME_REF_KINDS) {
+        name_ref_mod_path(p);
+    } else {
+        p.error("expected method name, field name or number");
+    }
     generic_args::opt_generic_arg_list_expr(p);
     if p.at(T!['(']) {
         arg_list(p);

src/tools/rust-analyzer/crates/parser/test_data/generated/runner.rs

@@ -844,6 +844,10 @@ mod err {
         run_and_expect_errors("test_data/parser/inline/err/pointer_type_no_mutability.rs");
     }
     #[test]
+    fn postfix_dot_expr_ambiguity() {
+        run_and_expect_errors("test_data/parser/inline/err/postfix_dot_expr_ambiguity.rs");
+    }
+    #[test]
     fn precise_capturing_invalid() {
         run_and_expect_errors("test_data/parser/inline/err/precise_capturing_invalid.rs");
     }

src/tools/rust-analyzer/crates/parser/test_data/parser/inline/err/postfix_dot_expr_ambiguity.rast

@@ -0,0 +1,29 @@
+SOURCE_FILE
+  FN
+    FN_KW "fn"
+    WHITESPACE " "
+    NAME
+      IDENT "foo"
+    PARAM_LIST
+      L_PAREN "("
+      R_PAREN ")"
+    WHITESPACE " "
+    BLOCK_EXPR
+      STMT_LIST
+        L_CURLY "{"
+        WHITESPACE "\n    "
+        METHOD_CALL_EXPR
+          PATH_EXPR
+            PATH
+              PATH_SEGMENT
+                NAME_REF
+                  IDENT "x"
+          DOT "."
+          WHITESPACE "\n    "
+          ARG_LIST
+            L_PAREN "("
+            R_PAREN ")"
+        WHITESPACE "\n"
+        R_CURLY "}"
+  WHITESPACE "\n"
+error 17: expected method name, field name or number

src/tools/rust-analyzer/crates/parser/test_data/parser/inline/err/postfix_dot_expr_ambiguity.rs

@@ -0,0 +1,4 @@
+fn foo() {
+    x.
+    ()
+}