Weak types must not have call or construct sigs

This changes the definition of weak types

Author: sandersn

src/compiler/checker.ts

@@ -9389,13 +9389,15 @@ namespace ts {
 
             /**
              * A type is 'weak' if it is an object type with at least one optional property
-             * and no required properties or index signatures
+             * and no required properties, call/construct signatures or index signatures
              */
             function isWeak(type: Type) {
                 const props = getPropertiesOfType(type);
                 return type.flags & TypeFlags.Object &&
                     props.length > 0 &&
                     every(props, p => !!(p.flags & SymbolFlags.Optional)) &&
+                    !getSignaturesOfType(type, SignatureKind.Call).length &&
+                    !getSignaturesOfType(type, SignatureKind.Construct).length &&
                     !getIndexTypeOfType(type, IndexKind.String) &&
                     !getIndexTypeOfType(type, IndexKind.Number);
             }

tests/baselines/reference/weakType.errors.txt

@@ -38,4 +38,14 @@ tests/cases/compiler/weakType.ts(31,18): error TS2345: Argument of type '{ error
 !!! error TS2345: Argument of type '{ error?: number; }' is not assignable to parameter of type 'ChangeOptions'.
 !!! error TS2345:   Weak type 'ChangeOptions' has no properties in common with '{ error?: number; }'.
     }
+    
+    class K {
+        constructor(s: string) { }
+    }
+    // Ctor isn't a weak type because it has a construct signature
+    interface Ctor {
+        new (s: string): K
+        n?: number
+    }
+    let ctor: Ctor = K
 

tests/baselines/reference/weakType.js

@@ -31,6 +31,16 @@ function del(options: ConfigurableStartEnd = {},
     changes.push(options);
     changes.push(error);
 }
+
+class K {
+    constructor(s: string) { }
+}
+// Ctor isn't a weak type because it has a construct signature
+interface Ctor {
+    new (s: string): K
+    n?: number
+}
+let ctor: Ctor = K
 
 
 //// [weakType.js]
@@ -48,3 +58,9 @@ function del(options, error) {
     changes.push(options);
     changes.push(error);
 }
+var K = (function () {
+    function K(s) {
+    }
+    return K;
+}());
+var ctor = K;

tests/cases/compiler/weakType.ts

@@ -30,3 +30,13 @@ function del(options: ConfigurableStartEnd = {},
     changes.push(options);
     changes.push(error);
 }
+
+class K {
+    constructor(s: string) { }
+}
+// Ctor isn't a weak type because it has a construct signature
+interface Ctor {
+    new (s: string): K
+    n?: number
+}
+let ctor: Ctor = K