Add test case for a predicate that throws

tests/baselines/reference/inferTypePredicates.errors.txt

@@ -284,4 +284,19 @@ inferTypePredicates.ts(205,7): error TS2741: Property 'z' is missing in type 'C1
     if (isNumOrStr(unk)) {
       let t: number | string = unk;  // should ok
     }
+    
+    // A function can be a type predicate even if it throws.
+    function assertAndPredicate(x: string | number | Date) {
+      if (x instanceof Date) {
+        throw new Error();
+      }
+      return typeof x === 'string';
+    }
+    
+    declare let snd: string | number | Date;
+    if (assertAndPredicate(snd)) {
+      let t: string = snd; // should ok
+    } else {
+      snd;  // type is number | Date
+    }
     

tests/baselines/reference/inferTypePredicates.js

@@ -241,6 +241,21 @@ declare let unk: unknown;
 if (isNumOrStr(unk)) {
   let t: number | string = unk;  // should ok
 }
+
+// A function can be a type predicate even if it throws.
+function assertAndPredicate(x: string | number | Date) {
+  if (x instanceof Date) {
+    throw new Error();
+  }
+  return typeof x === 'string';
+}
+
+declare let snd: string | number | Date;
+if (assertAndPredicate(snd)) {
+  let t: string = snd; // should ok
+} else {
+  snd;  // type is number | Date
+}
 
 
 //// [inferTypePredicates.js]
@@ -459,3 +474,16 @@ function isNumOrStr(x) {
 if (isNumOrStr(unk)) {
     var t = unk; // should ok
 }
+// A function can be a type predicate even if it throws.
+function assertAndPredicate(x) {
+    if (x instanceof Date) {
+        throw new Error();
+    }
+    return typeof x === 'string';
+}
+if (assertAndPredicate(snd)) {
+    var t = snd; // should ok
+}
+else {
+    snd; // type is number | Date
+}

tests/baselines/reference/inferTypePredicates.symbols

@@ -680,3 +680,37 @@ if (isNumOrStr(unk)) {
 >unk : Symbol(unk, Decl(inferTypePredicates.ts, 236, 11))
 }
 
+// A function can be a type predicate even if it throws.
+function assertAndPredicate(x: string | number | Date) {
+>assertAndPredicate : Symbol(assertAndPredicate, Decl(inferTypePredicates.ts, 239, 1))
+>x : Symbol(x, Decl(inferTypePredicates.ts, 242, 28))
+>Date : Symbol(Date, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.scripthost.d.ts, --, --))
+
+  if (x instanceof Date) {
+>x : Symbol(x, Decl(inferTypePredicates.ts, 242, 28))
+>Date : Symbol(Date, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.scripthost.d.ts, --, --))
+
+    throw new Error();
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+  }
+  return typeof x === 'string';
+>x : Symbol(x, Decl(inferTypePredicates.ts, 242, 28))
+}
+
+declare let snd: string | number | Date;
+>snd : Symbol(snd, Decl(inferTypePredicates.ts, 249, 11))
+>Date : Symbol(Date, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.scripthost.d.ts, --, --))
+
+if (assertAndPredicate(snd)) {
+>assertAndPredicate : Symbol(assertAndPredicate, Decl(inferTypePredicates.ts, 239, 1))
+>snd : Symbol(snd, Decl(inferTypePredicates.ts, 249, 11))
+
+  let t: string = snd; // should ok
+>t : Symbol(t, Decl(inferTypePredicates.ts, 251, 5))
+>snd : Symbol(snd, Decl(inferTypePredicates.ts, 249, 11))
+
+} else {
+  snd;  // type is number | Date
+>snd : Symbol(snd, Decl(inferTypePredicates.ts, 249, 11))
+}
+

tests/baselines/reference/inferTypePredicates.types

@@ -884,3 +884,41 @@ if (isNumOrStr(unk)) {
 >unk : string | number
 }
 
+// A function can be a type predicate even if it throws.
+function assertAndPredicate(x: string | number | Date) {
+>assertAndPredicate : (x: string | number | Date) => x is string
+>x : string | number | Date
+
+  if (x instanceof Date) {
+>x instanceof Date : boolean
+>x : string | number | Date
+>Date : DateConstructor
+
+    throw new Error();
+>new Error() : Error
+>Error : ErrorConstructor
+  }
+  return typeof x === 'string';
+>typeof x === 'string' : boolean
+>typeof x : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>x : string | number
+>'string' : "string"
+}
+
+declare let snd: string | number | Date;
+>snd : string | number | Date
+
+if (assertAndPredicate(snd)) {
+>assertAndPredicate(snd) : boolean
+>assertAndPredicate : (x: string | number | Date) => x is string
+>snd : string | number | Date
+
+  let t: string = snd; // should ok
+>t : string
+>snd : string
+
+} else {
+  snd;  // type is number | Date
+>snd : number | Date
+}
+

tests/cases/compiler/inferTypePredicates.ts

@@ -239,3 +239,18 @@ declare let unk: unknown;
 if (isNumOrStr(unk)) {
   let t: number | string = unk;  // should ok
 }
+
+// A function can be a type predicate even if it throws.
+function assertAndPredicate(x: string | number | Date) {
+  if (x instanceof Date) {
+    throw new Error();
+  }
+  return typeof x === 'string';
+}
+
+declare let snd: string | number | Date;
+if (assertAndPredicate(snd)) {
+  let t: string = snd; // should ok
+} else {
+  snd;  // type is number | Date
+}