Add regression test

tests/baselines/reference/exhaustiveSwitchCheckCircularity.errors.txt

@@ -0,0 +1,25 @@
+tests/cases/compiler/exhaustiveSwitchCheckCircularity.ts(14,26): error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
+
+
+==== tests/cases/compiler/exhaustiveSwitchCheckCircularity.ts (1 errors) ====
+    // Repro from #47539
+
+    declare function isNever(n: never): boolean;
+
+    function f() {
+        let foo: "aaa" | "bbb" = "aaa";
+        while (true) {
+            switch (foo) {
+                case "aaa":
+            }
+            if (foo === "aaa") {
+                foo = "bbb";
+            }
+            else if (isNever(foo)) {  // Error expected
+                             ~~~
+!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
+                break;
+            }
+        }
+    }
+

tests/baselines/reference/exhaustiveSwitchCheckCircularity.js

@@ -0,0 +1,38 @@
+//// [exhaustiveSwitchCheckCircularity.ts]
+// Repro from #47539
+
+declare function isNever(n: never): boolean;
+
+function f() {
+    let foo: "aaa" | "bbb" = "aaa";
+    while (true) {
+        switch (foo) {
+            case "aaa":
+        }
+        if (foo === "aaa") {
+            foo = "bbb";
+        }
+        else if (isNever(foo)) {  // Error expected
+            break;
+        }
+    }
+}
+
+
+//// [exhaustiveSwitchCheckCircularity.js]
+"use strict";
+// Repro from #47539
+function f() {
+    var foo = "aaa";
+    while (true) {
+        switch (foo) {
+            case "aaa":
+        }
+        if (foo === "aaa") {
+            foo = "bbb";
+        }
+        else if (isNever(foo)) { // Error expected
+            break;
+        }
+    }
+}

tests/baselines/reference/exhaustiveSwitchCheckCircularity.symbols

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+=== tests/cases/compiler/exhaustiveSwitchCheckCircularity.ts ===
+// Repro from #47539
+
+declare function isNever(n: never): boolean;
+>isNever : Symbol(isNever, Decl(exhaustiveSwitchCheckCircularity.ts, 0, 0))
+>n : Symbol(n, Decl(exhaustiveSwitchCheckCircularity.ts, 2, 25))
+
+function f() {
+>f : Symbol(f, Decl(exhaustiveSwitchCheckCircularity.ts, 2, 44))
+
+    let foo: "aaa" | "bbb" = "aaa";
+>foo : Symbol(foo, Decl(exhaustiveSwitchCheckCircularity.ts, 5, 7))
+
+    while (true) {
+        switch (foo) {
+>foo : Symbol(foo, Decl(exhaustiveSwitchCheckCircularity.ts, 5, 7))
+
+            case "aaa":
+        }
+        if (foo === "aaa") {
+>foo : Symbol(foo, Decl(exhaustiveSwitchCheckCircularity.ts, 5, 7))
+
+            foo = "bbb";
+>foo : Symbol(foo, Decl(exhaustiveSwitchCheckCircularity.ts, 5, 7))
+        }
+        else if (isNever(foo)) {  // Error expected
+>isNever : Symbol(isNever, Decl(exhaustiveSwitchCheckCircularity.ts, 0, 0))
+>foo : Symbol(foo, Decl(exhaustiveSwitchCheckCircularity.ts, 5, 7))
+
+            break;
+        }
+    }
+}
+

tests/baselines/reference/exhaustiveSwitchCheckCircularity.types

@@ -0,0 +1,43 @@
+=== tests/cases/compiler/exhaustiveSwitchCheckCircularity.ts ===
+// Repro from #47539
+
+declare function isNever(n: never): boolean;
+>isNever : (n: never) => boolean
+>n : never
+
+function f() {
+>f : () => void
+
+    let foo: "aaa" | "bbb" = "aaa";
+>foo : "aaa" | "bbb"
+>"aaa" : "aaa"
+
+    while (true) {
+>true : true
+
+        switch (foo) {
+>foo : "aaa" | "bbb"
+
+            case "aaa":
+>"aaa" : "aaa"
+        }
+        if (foo === "aaa") {
+>foo === "aaa" : boolean
+>foo : "aaa" | "bbb"
+>"aaa" : "aaa"
+
+            foo = "bbb";
+>foo = "bbb" : "bbb"
+>foo : "aaa" | "bbb"
+>"bbb" : "bbb"
+        }
+        else if (isNever(foo)) {  // Error expected
+>isNever(foo) : boolean
+>isNever : (n: never) => boolean
+>foo : "bbb"
+
+            break;
+        }
+    }
+}
+

tests/cases/compiler/exhaustiveSwitchCheckCircularity.ts

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+// @strict: true
+
+// Repro from #47539
+
+declare function isNever(n: never): boolean;
+
+function f() {
+    let foo: "aaa" | "bbb" = "aaa";
+    while (true) {
+        switch (foo) {
+            case "aaa":
+        }
+        if (foo === "aaa") {
+            foo = "bbb";
+        }
+        else if (isNever(foo)) {  // Error expected
+            break;
+        }
+    }
+}