fix: add diagnose for non-declarative statements in namespace (#2765)

Author: JesseCodeBones

src/diagnosticMessages.json

@@ -194,6 +194,7 @@
   "Cannot extend a class '{0}'. Class constructor is marked as private.": 2675,
   "The 'this' types of each signature are incompatible.": 2685,
   "Namespace '{0}' has no exported member '{1}'.": 2694,
+  "Namespace can only have declarations.": 2695,
   "Required type parameters may not follow optional type parameters.": 2706,
   "Duplicate property '{0}'.": 2718,
   "Property '{0}' is missing in type '{1}' but required in type '{2}'.": 2741,

src/parser.ts

@@ -398,9 +398,14 @@ export class Parser extends DiagnosticEmitter {
               tn.range(declareStart, declareEnd), "declare"
             ); // recoverable
           }
-          if (!namespace) {
+          if (namespace) {
+            this.error(
+              DiagnosticCode.Namespace_can_only_have_declarations,
+              tn.range(startPos)
+            );
+          } else {
             statement = this.parseStatement(tn, true);
-          } // TODO: else?
+          }
         }
         break;
       }

tests/parser/namespace.ts

@@ -1,7 +1,9 @@
+let outerVar:i32 = 0;
 declare namespace A {
   namespace B {
     export namespace C {
       var aVar: i32;
+      outerVar = 42; // 2695: Namespace can only have declarations.
       const aConst: i32;
       const aConstInvalid: i32 = 0; // 1039: Initializers are not allowed in ambient contexts.
       function aFunc(): void;

tests/parser/namespace.ts.fixture.ts

@@ -1,3 +1,4 @@
+let outerVar: i32 = 0;
 declare namespace A {
   namespace B {
     export namespace C {
@@ -14,5 +15,6 @@ declare namespace A {
     }
   }
 }
-// ERROR 1039: "Initializers are not allowed in ambient contexts." in namespace.ts(6,32+1)
-// ERROR 1183: "An implementation cannot be declared in ambient contexts." in namespace.ts(8,37+1)
+// ERROR 2695: "Namespace can only have declarations." in namespace.ts(6,7+0)
+// ERROR 1039: "Initializers are not allowed in ambient contexts." in namespace.ts(8,32+1)
+// ERROR 1183: "An implementation cannot be declared in ambient contexts." in namespace.ts(10,37+1)