extract and test inference context

src/typeck.test.ts

@@ -0,0 +1,36 @@
+import { TY_INT, TY_STRING } from "./ast";
+import { DUMMY_SPAN as SPAN } from "./error";
+import { InferContext } from "./typeck";
+
+it("should infer types across assignments", () => {
+  const infcx = new InferContext();
+
+  const a = infcx.newVar();
+  const b = infcx.newVar();
+  const c = infcx.newVar();
+
+  infcx.assign(a, b, SPAN);
+  infcx.assign(b, c, SPAN);
+
+  infcx.assign(a, TY_INT, SPAN);
+
+  const aTy = infcx.resolveIfPossible(c);
+  const bTy = infcx.resolveIfPossible(c);
+  const cTy = infcx.resolveIfPossible(c);
+
+  expect(aTy.kind).toEqual("int");
+  expect(bTy.kind).toEqual("int");
+  expect(cTy.kind).toEqual("int");
+});
+
+it("should conflict assignments to resolvable type vars", () => {
+  const infcx = new InferContext();
+
+  const a = infcx.newVar();
+  const b = infcx.newVar();
+
+  infcx.assign(a, b, SPAN);
+  infcx.assign(b, TY_INT, SPAN);
+
+  expect(() => infcx.assign(a, TY_STRING, SPAN)).toThrow();
+});