Add conditions to check for class extension or implementation of prim… #55712

qwefgh90 · 2023-09-11T14:53:39Z

fixes unresolved issues that discussed on #49208.

Example

Class implementing the primitive:

class C implements number { }
class C2 implements string { }
class C3 implements boolean { }

Actual behavior:

'number' only refers to a type, but is being used as a value here.
'string' only refers to a type, but is being used as a value here.
'boolean' only refers to a type, but is being used as a value here.

Improvement:

A class cannot implement a primitive type like 'number'; a class can only implement interfaces.
A class cannot implement a primitive type like 'string'; a class can only implement interfaces.
A class cannot implement a primitive type like 'boolean'; a class can only implement interfaces.

Class extending the primitive:

class C extends number { }
class C2 extends string { }
class C3 extends boolean { }

Actual behavior:

'number' only refers to a type, but is being used as a value here.
'string' only refers to a type, but is being used as a value here.
'boolean' only refers to a type, but is being used as a value here.

Improvement:

A class cannot extend a primitive type like 'number'; a class can only extend named types and classes.
A class cannot extend a primitive type like 'string'; a class can only extend named types and classes.
A class cannot extend a primitive type like 'boolean'; a class can only extend named types and classes.

Notes:

gulp runtests passed on current branch.
The errors related to implement weren't covered by current unit tests. I added a new test tests\cases\compiler\classImplementsPrimitive.ts to test classes implementing primitive types.
I updated a few unit tests to test for the error.
I made additional changes for some minor typos.

Description

PR #49208 was initially created to address issue #46246 along with some related problems.

However, that issue #46246 has been resolved by a different PR. So, PR #49208 wasn't merged and It was closed while leaving some issues that had been newly found and discussed in this PR, specifically related to incorrect error messages where classes extends or implements primitive types, as shown in the examples above.

To address these issue, I have made changes to the checkAndReportErrorForUsingTypeAsValue function, which has been responsible for these kinds of errors since #46357 was merged.

I have added new functions, isExtendedByClass and isImplementedByClass which determine if errorLocation 's grandparent contains SyntaxKind.ImplementsKeyword or SyntaxKind.ExtendsKeyword. If a condition evaluates to true, the relevant error message is emitted.

I would appreciate any feedback!

typescript-bot · 2023-09-11T14:53:47Z

This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise.

DanielRosenwasser · 2023-09-11T19:04:05Z

The errors are no longer exactly correct. They should be

An interface cannot extend a primitive type like '{0}'. It can only extend other named object types.

A class cannot implement a primitive type like '{0}'. It can only extend other named object types.

A class cannot extend a primitive type like '{0}'. Classes can only extend constructable values.

sandersn · 2023-09-21T22:41:53Z

src/compiler/diagnosticMessages.json

+        "category": "Error",
+        "code": 2855
+    },
+    "A class cannot implement a primitive type like '{0}'. It can only extend other named object types.": {


Should this message refer to 'implement' both times? Seems like it should but I'm not sure.

Suggested change

"A class cannot implement a primitive type like '{0}'. It can only extend other named object types.": {

"A class cannot implement a primitive type like '{0}'. It can only implement other named object types.": {

You're right, that looks a typo. 'implement' would be better in this context.

src/compiler/checker.ts

sandersn · 2023-09-21T22:48:24Z