fix(54760): Report error for 'declare type' followed by newline (#54761)

Author: strager

src/compiler/parser.ts

@@ -7106,11 +7106,17 @@ namespace Parser {
                 case SyntaxKind.ProtectedKeyword:
                 case SyntaxKind.PublicKeyword:
                 case SyntaxKind.ReadonlyKeyword:
+                    const previousToken = token();
                     nextToken();
                     // ASI takes effect for this modifier.
                     if (scanner.hasPrecedingLineBreak()) {
                         return false;
                     }
+                    if (previousToken === SyntaxKind.DeclareKeyword && token() === SyntaxKind.TypeKeyword) {
+                        // If we see 'declare type', then commit to parsing a type alias. parseTypeAliasDeclaration will
+                        // report Line_break_not_permitted_here if needed.
+                        return true;
+                    }
                     continue;
 
                 case SyntaxKind.GlobalKeyword:
@@ -8107,6 +8113,9 @@ namespace Parser {
 
     function parseTypeAliasDeclaration(pos: number, hasJSDoc: boolean, modifiers: NodeArray<ModifierLike> | undefined): TypeAliasDeclaration {
         parseExpected(SyntaxKind.TypeKeyword);
+        if (scanner.hasPrecedingLineBreak()) {
+            parseErrorAtCurrentToken(Diagnostics.Line_break_not_permitted_here);
+        }
         const name = parseIdentifier();
         const typeParameters = parseTypeParameters();
         parseExpected(SyntaxKind.EqualsToken);

tests/baselines/reference/typeAliasDeclareKeywordNewlines.errors.txt

@@ -0,0 +1,26 @@
+typeAliasDeclareKeywordNewlines.ts(5,1): error TS1142: Line break not permitted here.
+
+
+==== typeAliasDeclareKeywordNewlines.ts (1 errors) ====
+    var declare: string, type: number;
+    
+    // The following is invalid but should declare a type alias named 'T1':
+    declare type /*unexpected newline*/
+    T1 = null;
+    ~~
+!!! error TS1142: Line break not permitted here.
+    const t1: T1 = null; // Assert that T1 is the null type.
+    
+    let T: null;
+    // The following should use a variable named 'declare', use a variable named
+    // 'type', and assign to a variable named 'T'.
+    declare /*ASI*/
+    type /*ASI*/
+    T = null;
+    
+    // The following should use a variable named 'declare' and declare a type alias
+    // named 'T2':
+    declare /*ASI*/
+    type T2 = null;
+    const t2: T2 = null; // Assert that T2 is the null type.
+    

tests/baselines/reference/typeAliasDeclareKeywordNewlines.js

@@ -0,0 +1,37 @@
+//// [tests/cases/compiler/typeAliasDeclareKeywordNewlines.ts] ////
+
+//// [typeAliasDeclareKeywordNewlines.ts]
+var declare: string, type: number;
+
+// The following is invalid but should declare a type alias named 'T1':
+declare type /*unexpected newline*/
+T1 = null;
+const t1: T1 = null; // Assert that T1 is the null type.
+
+let T: null;
+// The following should use a variable named 'declare', use a variable named
+// 'type', and assign to a variable named 'T'.
+declare /*ASI*/
+type /*ASI*/
+T = null;
+
+// The following should use a variable named 'declare' and declare a type alias
+// named 'T2':
+declare /*ASI*/
+type T2 = null;
+const t2: T2 = null; // Assert that T2 is the null type.
+
+
+//// [typeAliasDeclareKeywordNewlines.js]
+var declare, type;
+var t1 = null; // Assert that T1 is the null type.
+var T;
+// The following should use a variable named 'declare', use a variable named
+// 'type', and assign to a variable named 'T'.
+declare; /*ASI*/
+type; /*ASI*/
+T = null;
+// The following should use a variable named 'declare' and declare a type alias
+// named 'T2':
+declare; /*ASI*/
+var t2 = null; // Assert that T2 is the null type.

tests/baselines/reference/typeAliasDeclareKeywordNewlines.symbols

@@ -0,0 +1,42 @@
+//// [tests/cases/compiler/typeAliasDeclareKeywordNewlines.ts] ////
+
+=== typeAliasDeclareKeywordNewlines.ts ===
+var declare: string, type: number;
+>declare : Symbol(declare, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 3))
+>type : Symbol(type, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 20))
+
+// The following is invalid but should declare a type alias named 'T1':
+declare type /*unexpected newline*/
+T1 = null;
+>T1 : Symbol(T1, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 34))
+
+const t1: T1 = null; // Assert that T1 is the null type.
+>t1 : Symbol(t1, Decl(typeAliasDeclareKeywordNewlines.ts, 5, 5))
+>T1 : Symbol(T1, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 34))
+
+let T: null;
+>T : Symbol(T, Decl(typeAliasDeclareKeywordNewlines.ts, 7, 3))
+
+// The following should use a variable named 'declare', use a variable named
+// 'type', and assign to a variable named 'T'.
+declare /*ASI*/
+>declare : Symbol(declare, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 3))
+
+type /*ASI*/
+>type : Symbol(type, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 20))
+
+T = null;
+>T : Symbol(T, Decl(typeAliasDeclareKeywordNewlines.ts, 7, 3))
+
+// The following should use a variable named 'declare' and declare a type alias
+// named 'T2':
+declare /*ASI*/
+>declare : Symbol(declare, Decl(typeAliasDeclareKeywordNewlines.ts, 0, 3))
+
+type T2 = null;
+>T2 : Symbol(T2, Decl(typeAliasDeclareKeywordNewlines.ts, 16, 7))
+
+const t2: T2 = null; // Assert that T2 is the null type.
+>t2 : Symbol(t2, Decl(typeAliasDeclareKeywordNewlines.ts, 18, 5))
+>T2 : Symbol(T2, Decl(typeAliasDeclareKeywordNewlines.ts, 16, 7))
+

tests/baselines/reference/typeAliasDeclareKeywordNewlines.types

@@ -0,0 +1,41 @@
+//// [tests/cases/compiler/typeAliasDeclareKeywordNewlines.ts] ////
+
+=== typeAliasDeclareKeywordNewlines.ts ===
+var declare: string, type: number;
+>declare : string
+>type : number
+
+// The following is invalid but should declare a type alias named 'T1':
+declare type /*unexpected newline*/
+T1 = null;
+>T1 : null
+
+const t1: T1 = null; // Assert that T1 is the null type.
+>t1 : null
+
+let T: null;
+>T : null
+
+// The following should use a variable named 'declare', use a variable named
+// 'type', and assign to a variable named 'T'.
+declare /*ASI*/
+>declare : string
+
+type /*ASI*/
+>type : number
+
+T = null;
+>T = null : null
+>T : null
+
+// The following should use a variable named 'declare' and declare a type alias
+// named 'T2':
+declare /*ASI*/
+>declare : string
+
+type T2 = null;
+>T2 : null
+
+const t2: T2 = null; // Assert that T2 is the null type.
+>t2 : null
+

tests/cases/compiler/typeAliasDeclareKeywordNewlines.ts

@@ -0,0 +1,19 @@
+var declare: string, type: number;
+
+// The following is invalid but should declare a type alias named 'T1':
+declare type /*unexpected newline*/
+T1 = null;
+const t1: T1 = null; // Assert that T1 is the null type.
+
+let T: null;
+// The following should use a variable named 'declare', use a variable named
+// 'type', and assign to a variable named 'T'.
+declare /*ASI*/
+type /*ASI*/
+T = null;
+
+// The following should use a variable named 'declare' and declare a type alias
+// named 'T2':
+declare /*ASI*/
+type T2 = null;
+const t2: T2 = null; // Assert that T2 is the null type.