Disallow whitespace before non-null assertion

src/compiler/diagnosticMessages.json

@@ -951,6 +951,10 @@
         "category": "Error",
         "code": 1288
     },
+    "A non-null assertion may not be preceded by whitespace.": {
+        "category": "Error",
+        "code": 1289
+    },
 
     "'with' statements are not allowed in an async function block.": {
         "category": "Error",

src/compiler/parser.ts

@@ -6438,8 +6438,12 @@ namespace Parser {
 
             if (!questionDotToken) {
                 if (token() === SyntaxKind.ExclamationToken && !scanner.hasPrecedingLineBreak()) {
+                    const start = scanner.getTokenFullStart();
                     nextToken();
                     expression = finishNode(factory.createNonNullExpression(expression), pos);
+                    if (expression.end - start !== 1) {
+                        parseErrorAt(start, expression.end, Diagnostics.A_non_null_assertion_may_not_be_preceded_by_whitespace);
+                    }
                     continue;
                 }
                 const typeArguments = tryParse(parseTypeArgumentsInExpression);

tests/baselines/reference/parseNoWhitespaceBeforeExclamation.errors.txt

@@ -0,0 +1,18 @@
+parseNoWhitespaceBeforeExclamation.ts(3,6): error TS1289: A non-null assertion may not be preceded by whitespace.
+parseNoWhitespaceBeforeExclamation.ts(4,6): error TS1289: A non-null assertion may not be preceded by whitespace.
+parseNoWhitespaceBeforeExclamation.ts(5,6): error TS1289: A non-null assertion may not be preceded by whitespace.
+
+
+==== parseNoWhitespaceBeforeExclamation.ts (3 errors) ====
+    declare var value: any;
+
+    value !;
+         ~~
+!!! error TS1289: A non-null assertion may not be preceded by whitespace.
+    value !instanceof String;
+         ~~
+!!! error TS1289: A non-null assertion may not be preceded by whitespace.
+    value/* this is a comment */! instanceof String;
+         ~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS1289: A non-null assertion may not be preceded by whitespace.
+

tests/baselines/reference/parseNoWhitespaceBeforeExclamation.js

@@ -0,0 +1,14 @@
+//// [tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts] ////
+
+//// [parseNoWhitespaceBeforeExclamation.ts]
+declare var value: any;
+
+value !;
+value !instanceof String;
+value/* this is a comment */! instanceof String;
+
+
+//// [parseNoWhitespaceBeforeExclamation.js]
+value;
+value instanceof String;
+value /* this is a comment */ instanceof String;

tests/baselines/reference/parseNoWhitespaceBeforeExclamation.symbols

@@ -0,0 +1,17 @@
+//// [tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts] ////
+
+=== parseNoWhitespaceBeforeExclamation.ts ===
+declare var value: any;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+
+value !;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+
+value !instanceof String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+value/* this is a comment */! instanceof String;
+>value : Symbol(value, Decl(parseNoWhitespaceBeforeExclamation.ts, 0, 11))
+>String : Symbol(String, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+

tests/baselines/reference/parseNoWhitespaceBeforeExclamation.types

@@ -0,0 +1,22 @@
+//// [tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts] ////
+
+=== parseNoWhitespaceBeforeExclamation.ts ===
+declare var value: any;
+>value : any
+
+value !;
+>value ! : any
+>value : any
+
+value !instanceof String;
+>value !instanceof String : boolean
+>value ! : any
+>value : any
+>String : StringConstructor
+
+value/* this is a comment */! instanceof String;
+>value/* this is a comment */! instanceof String : boolean
+>value/* this is a comment */! : any
+>value : any
+>String : StringConstructor
+

tests/cases/compiler/parseNoWhitespaceBeforeExclamation.ts

@@ -0,0 +1,5 @@
+declare var value: any;
+
+value !;
+value !instanceof String;
+value/* this is a comment */! instanceof String;