Fix incorrect parser error assumption in semicolon handling leading to incremental parser brokenness (#48067)

Author: jakebailey

Diff for: src/compiler/parser.ts

@@ -1681,19 +1681,8 @@ namespace ts {
                 return;
             }
 
-            // If an initializer was parsed but there is still an error in finding the next semicolon,
-            // we generally know there was an error already reported in the initializer...
-            //   class Example { a = new Map([), ) }
-            //                                ~
             if (initializer) {
-                // ...unless we've found the start of a block after a property declaration, in which
-                // case we can know that regardless of the initializer we should complain on the block.
-                //   class Example { a = 0 {} }
-                //                         ~
-                if (token() === SyntaxKind.OpenBraceToken) {
-                    parseErrorAtCurrentToken(Diagnostics._0_expected, tokenToString(SyntaxKind.SemicolonToken));
-                }
-
+                parseErrorAtCurrentToken(Diagnostics._0_expected, tokenToString(SyntaxKind.SemicolonToken));
                 return;
             }
 

Diff for: tests/baselines/reference/parser0_004152.errors.txt

@@ -1,6 +1,6 @@
 tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,28): error TS2304: Cannot find name 'DisplayPosition'.
 tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,45): error TS1137: Expression or comma expected.
-tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,46): error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
+tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,46): error TS1005: ';' expected.
 tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,49): error TS1005: ';' expected.
 tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,51): error TS2300: Duplicate identifier '3'.
 tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(2,52): error TS1005: ';' expected.
@@ -41,7 +41,7 @@ tests/cases/conformance/parser/ecmascript5/Fuzz/parser0_004152.ts(3,25): error T
                                                 ~
 !!! error TS1137: Expression or comma expected.
                                                  ~
-!!! error TS1068: Unexpected token. A constructor, method, accessor, or property was expected.
+!!! error TS1005: ';' expected.
                                                     ~
 !!! error TS1005: ';' expected.
                                                       ~

Diff for: tests/cases/fourslash/parserCorruptionAfterMapInClass.ts

@@ -0,0 +1,17 @@
+/// <reference path="fourslash.ts" />
+
+// @target: esnext
+// @lib: es2015
+// @strict: true
+
+//// class C {
+////     map = new Set<string, number>/*$*/
+////
+////     foo() {
+////
+////     }
+//// }
+
+goTo.marker('$');
+edit.insert('()');
+verify.getSyntacticDiagnostics([]);