fix(compiler-cli): allow '==' to compare nullable types (#16731)

Fixes: #16729

* fix(compiler-cli): diagnose issues in conditional of ternary

Fixes: #16730

packages/compiler-cli/src/diagnostics/expression_type.ts

@@ -51,8 +51,29 @@ export class AstType implements AstVisitor {
       return kind;
     }
 
-    const leftType = this.getType(ast.left);
-    const rightType = this.getType(ast.right);
+    const getType = (ast: AST, operation: string): Symbol => {
+      const type = this.getType(ast);
+      if (type.nullable) {
+        switch (operation) {
+          case '&&':
+          case '||':
+          case '==':
+          case '!=':
+          case '===':
+          case '!==':
+            // Nullable allowed.
+            break;
+          default:
+            this.reportError(`The expression might be null`, ast);
+            break;
+        }
+        return this.query.getNonNullableType(type);
+      }
+      return type;
+    };
+
+    const leftType = getType(ast.left, ast.operation);
+    const rightType = getType(ast.right, ast.operation);
     const leftRawKind = this.query.getTypeKind(leftType);
     const rightRawKind = this.query.getTypeKind(rightType);
     const leftKind = normalize(leftRawKind, rightRawKind);
@@ -166,6 +187,9 @@ export class AstType implements AstVisitor {
 
   visitConditional(ast: Conditional) {
     // The type of a conditional is the union of the true and false conditions.
+    if (this.diagnostics) {
+      visitAstChildren(ast, this);
+    }
     return this.query.getTypeUnion(this.getType(ast.trueExp), this.getType(ast.falseExp));
   }
 

packages/compiler-cli/test/diagnostics/expression_diagnostics_spec.ts

@@ -175,7 +175,16 @@ describe('expression diagnostics', () => {
   it('should reject an uncalled event handler',
      () => reject(
          '<div (click)="click">{{person.name.first}}</div>', 'Unexpected callable expression'));
-
+  describe('with comparisions between nullable and non-nullable', () => {
+    it('should accept ==', () => accept(`<div>{{e == 1 ? 'a' : 'b'}}</div>`));
+    it('should accept ===', () => accept(`<div>{{e === 1 ? 'a' : 'b'}}</div>`));
+    it('should accept !=', () => accept(`<div>{{e != 1 ? 'a' : 'b'}}</div>`));
+    it('should accept !==', () => accept(`<div>{{e !== 1 ? 'a' : 'b'}}</div>`));
+    it('should accept &&', () => accept(`<div>{{e && 1 ? 'a' : 'b'}}</div>`));
+    it('should accept ||', () => accept(`<div>{{e || 1 ? 'a' : 'b'}}</div>`));
+    it('should reject >',
+       () => reject(`<div>{{e > 1 ? 'a' : 'b'}}</div>`, 'The expression might be null'));
+  });
 });
 
 const FILES: Directory = {
@@ -216,6 +225,7 @@ const FILES: Directory = {
           promised_people: Promise<Person[]>;
           private private_person: Person;
           private private_people: Person[];
+          e?: number;
 
           getPerson(): Person { return this.person; }
           click() {}