[ASDAlexander77]

Found in EventTarget.ts of the BrowserLib sources attached to #231. That is the can't find type by name: EventListenerCallback item listed there: the error was a symptom of this bug.

const m: Map<string, number[]> = new Map();   // crashed at run time (0xC0000005)
m.set("a", [5]);

class Box<T> { … }
const b: Box<number> = new Box();              // error: Generic class 'Box' is missing type arguments

TypeScript takes the type arguments of new C() from the type the value is given to. tslang did not:

• A generic with type-parameter defaults: Map is class Map<K = any, V = any>, so new Map() became Map<any, any>. The initializer then cast it to Map<string, number[]>, a different specialization with a different layout. The first set crashed at run time. This happens on older builds too.
• A generic without defaults: a compile error.

Fix

In mlirGen(NewExpression), a new written without type arguments uses the receiver's type when that type is a specialization of the same generic class. The comparison uses ClassInfo::originClassType. It applies when the class named is either the generic itself or its specialization by the defaults.

The receiver is the receiverType that is already passed down for:

• a declared variable;
• a field initializer;
• the right side of an assignment.

Explicit type arguments are unchanged, and so is a receiver of any other type.

Tests

• New 00new_generic_from_receiver.ts (compile, jit, and the rc/none corpus). It covers:

  • a plain generic;
  • a generic with defaults;
  • a declared variable, an assignment, a field initializer and a constructor assignment;
  • explicit type arguments.

  The old build fails it with "missing type arguments".

• Full release suite: 2993/2993 passed.

• TypeScriptCompilerDefaultLib tests, release jit and compile: 156/156 each.

• BrowserLib EventTarget.ts no longer reports EventListenerCallback. What is left there is the existing rule that push on a const local array is an error, plus the missing splice.

Not in this PR

A cast between two different specializations of one generic class, such as Map<any, any> to Map<string, number[]>, is still accepted silently. That is what turned this into a run-time crash. It should be a compile error.

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