test: add failing test for microsoft#19577

Author: nicolas377

tests/baselines/reference/nonNullFullInference.js

@@ -0,0 +1,33 @@
+//// [nonNullFullInference.ts]
+// https://github.com/microsoft/TypeScript/issues/19577
+
+function testNonNullInference(numbers: number[]) {
+    let last;
+
+    for (const n of numbers) {
+        if (n % 2) {
+            return n;
+        }
+
+        last = n;
+    }
+
+    last; // number | undefined
+    last!; // number
+}
+
+
+//// [nonNullFullInference.js]
+// https://github.com/microsoft/TypeScript/issues/19577
+function testNonNullInference(numbers) {
+    var last;
+    for (var _i = 0, numbers_1 = numbers; _i < numbers_1.length; _i++) {
+        var n = numbers_1[_i];
+        if (n % 2) {
+            return n;
+        }
+        last = n;
+    }
+    last; // number | undefined
+    last; // number
+}

tests/baselines/reference/nonNullFullInference.symbols

@@ -0,0 +1,33 @@
+=== tests/cases/compiler/nonNullFullInference.ts ===
+// https://github.com/microsoft/TypeScript/issues/19577
+
+function testNonNullInference(numbers: number[]) {
+>testNonNullInference : Symbol(testNonNullInference, Decl(nonNullFullInference.ts, 0, 0))
+>numbers : Symbol(numbers, Decl(nonNullFullInference.ts, 2, 30))
+
+    let last;
+>last : Symbol(last, Decl(nonNullFullInference.ts, 3, 7))
+
+    for (const n of numbers) {
+>n : Symbol(n, Decl(nonNullFullInference.ts, 5, 14))
+>numbers : Symbol(numbers, Decl(nonNullFullInference.ts, 2, 30))
+
+        if (n % 2) {
+>n : Symbol(n, Decl(nonNullFullInference.ts, 5, 14))
+
+            return n;
+>n : Symbol(n, Decl(nonNullFullInference.ts, 5, 14))
+        }
+
+        last = n;
+>last : Symbol(last, Decl(nonNullFullInference.ts, 3, 7))
+>n : Symbol(n, Decl(nonNullFullInference.ts, 5, 14))
+    }
+
+    last; // number | undefined
+>last : Symbol(last, Decl(nonNullFullInference.ts, 3, 7))
+
+    last!; // number
+>last : Symbol(last, Decl(nonNullFullInference.ts, 3, 7))
+}
+

tests/baselines/reference/nonNullFullInference.types

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+=== tests/cases/compiler/nonNullFullInference.ts ===
+// https://github.com/microsoft/TypeScript/issues/19577
+
+function testNonNullInference(numbers: number[]) {
+>testNonNullInference : (numbers: number[]) => number
+>numbers : number[]
+
+    let last;
+>last : any
+
+    for (const n of numbers) {
+>n : number
+>numbers : number[]
+
+        if (n % 2) {
+>n % 2 : number
+>n : number
+>2 : 2
+
+            return n;
+>n : number
+        }
+
+        last = n;
+>last = n : number
+>last : any
+>n : number
+    }
+
+    last; // number | undefined
+>last : number | undefined
+
+    last!; // number
+>last! : number
+>last : number | undefined
+}
+

tests/cases/compiler/nonNullFullInference.ts

@@ -0,0 +1,17 @@
+// @noImplicitAny: true
+// https://github.com/microsoft/TypeScript/issues/19577
+
+function testNonNullInference(numbers: number[]) {
+    let last;
+
+    for (const n of numbers) {
+        if (n % 2) {
+            return n;
+        }
+
+        last = n;
+    }
+
+    last; // number | undefined
+    last!; // number
+}