Fixed type predicate inference for discriminated union parameters (#5…

…7952)
microsoft · Apr 2, 2024 · 42a215c · 42a215c
1 parent 4cedfe4
commit 42a215c
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Showing 6 changed files with 133 additions and 3 deletions.
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -37690,8 +37690,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             { flags: FlowFlags.Start };
         const trueCondition: FlowCondition = {
             flags: FlowFlags.TrueCondition,
-            node: expr,
             antecedent,
+            node: expr,
         };
 
         const trueType = getFlowTypeOfReference(param.name, initType, initType, func, trueCondition);
@@ -37700,10 +37700,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // "x is T" means that x is T if and only if it returns true. If it returns false then x is not T.
         // This means that if the function is called with an argument of type trueType, there can't be anything left in the `else` branch. It must reduce to `never`.
         const falseCondition: FlowCondition = {
-            ...trueCondition,
             flags: FlowFlags.FalseCondition,
+            antecedent,
+            node: expr,
         };
-        const falseSubtype = getFlowTypeOfReference(param.name, trueType, trueType, func, falseCondition);
+        const falseSubtype = getFlowTypeOfReference(param.name, initType, trueType, func, falseCondition);
         return falseSubtype.flags & TypeFlags.Never ? trueType : undefined;
     }
 

diff --git a/tests/baselines/reference/inferTypePredicates.errors.txt b/tests/baselines/reference/inferTypePredicates.errors.txt
@@ -315,4 +315,14 @@ inferTypePredicates.ts(205,7): error TS2741: Property 'z' is missing in type 'C1
     function inferWithRest(x: string | null, ...f: ["a", "b"]) {
       return typeof x === 'string';
     }
+
+    // https://github.com/microsoft/TypeScript/issues/57947
+    declare const foobar:
+      | { type: "foo"; foo: number }
+      | { type: "bar"; bar: string };
+
+    const foobarPred = (fb: typeof foobar) => fb.type === "foo";
+    if (foobarPred(foobar)) {
+      foobar.foo;
+    }
 
diff --git a/tests/baselines/reference/inferTypePredicates.js b/tests/baselines/reference/inferTypePredicates.js
@@ -269,6 +269,16 @@ const noInferenceFromImpossibleRest = (...f: []) => typeof f === "undefined";
 function inferWithRest(x: string | null, ...f: ["a", "b"]) {
   return typeof x === 'string';
 }
+
+// https://github.com/microsoft/TypeScript/issues/57947
+declare const foobar:
+  | { type: "foo"; foo: number }
+  | { type: "bar"; bar: string };
+
+const foobarPred = (fb: typeof foobar) => fb.type === "foo";
+if (foobarPred(foobar)) {
+  foobar.foo;
+}
 
 
 //// [inferTypePredicates.js]
@@ -524,6 +534,10 @@ function inferWithRest(x) {
     }
     return typeof x === 'string';
 }
+var foobarPred = function (fb) { return fb.type === "foo"; };
+if (foobarPred(foobar)) {
+    foobar.foo;
+}
 
 
 //// [inferTypePredicates.d.ts]
@@ -605,3 +619,14 @@ declare function narrowFromAny(x: any): x is number;
 declare const noInferenceFromRest: (f_0: "a" | "b") => boolean;
 declare const noInferenceFromImpossibleRest: () => boolean;
 declare function inferWithRest(x: string | null, ...f: ["a", "b"]): x is string;
+declare const foobar: {
+    type: "foo";
+    foo: number;
+} | {
+    type: "bar";
+    bar: string;
+};
+declare const foobarPred: (fb: typeof foobar) => fb is {
+    type: "foo";
+    foo: number;
+};
diff --git a/tests/baselines/reference/inferTypePredicates.symbols b/tests/baselines/reference/inferTypePredicates.symbols
@@ -747,3 +747,33 @@ function inferWithRest(x: string | null, ...f: ["a", "b"]) {
 >x : Symbol(x, Decl(inferTypePredicates.ts, 265, 23))
 }
 
+// https://github.com/microsoft/TypeScript/issues/57947
+declare const foobar:
+>foobar : Symbol(foobar, Decl(inferTypePredicates.ts, 270, 13))
+
+  | { type: "foo"; foo: number }
+>type : Symbol(type, Decl(inferTypePredicates.ts, 271, 5))
+>foo : Symbol(foo, Decl(inferTypePredicates.ts, 271, 18))
+
+  | { type: "bar"; bar: string };
+>type : Symbol(type, Decl(inferTypePredicates.ts, 272, 5))
+>bar : Symbol(bar, Decl(inferTypePredicates.ts, 272, 18))
+
+const foobarPred = (fb: typeof foobar) => fb.type === "foo";
+>foobarPred : Symbol(foobarPred, Decl(inferTypePredicates.ts, 274, 5))
+>fb : Symbol(fb, Decl(inferTypePredicates.ts, 274, 20))
+>foobar : Symbol(foobar, Decl(inferTypePredicates.ts, 270, 13))
+>fb.type : Symbol(type, Decl(inferTypePredicates.ts, 271, 5), Decl(inferTypePredicates.ts, 272, 5))
+>fb : Symbol(fb, Decl(inferTypePredicates.ts, 274, 20))
+>type : Symbol(type, Decl(inferTypePredicates.ts, 271, 5), Decl(inferTypePredicates.ts, 272, 5))
+
+if (foobarPred(foobar)) {
+>foobarPred : Symbol(foobarPred, Decl(inferTypePredicates.ts, 274, 5))
+>foobar : Symbol(foobar, Decl(inferTypePredicates.ts, 270, 13))
+
+  foobar.foo;
+>foobar.foo : Symbol(foo, Decl(inferTypePredicates.ts, 271, 18))
+>foobar : Symbol(foobar, Decl(inferTypePredicates.ts, 270, 13))
+>foo : Symbol(foo, Decl(inferTypePredicates.ts, 271, 18))
+}
+
diff --git a/tests/baselines/reference/inferTypePredicates.types b/tests/baselines/reference/inferTypePredicates.types
@@ -1595,3 +1595,57 @@ function inferWithRest(x: string | null, ...f: ["a", "b"]) {
 >         : ^^^^^^^^
 }
 
+// https://github.com/microsoft/TypeScript/issues/57947
+declare const foobar:
+>foobar : { type: "foo"; foo: number; } | { type: "bar"; bar: string; }
+>       : ^^^^^^^^     ^^^^^^^      ^^^^^^^^^^^^^^     ^^^^^^^      ^^^
+
+  | { type: "foo"; foo: number }
+>type : "foo"
+>     : ^^^^^
+>foo : number
+>    : ^^^^^^
+
+  | { type: "bar"; bar: string };
+>type : "bar"
+>     : ^^^^^
+>bar : string
+>    : ^^^^^^
+
+const foobarPred = (fb: typeof foobar) => fb.type === "foo";
+>foobarPred : (fb: typeof foobar) => fb is { type: "foo"; foo: number; }
+>           : ^^^^^             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>(fb: typeof foobar) => fb.type === "foo" : (fb: typeof foobar) => fb is { type: "foo"; foo: number; }
+>                                         : ^^^^^             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>fb : { type: "foo"; foo: number; } | { type: "bar"; bar: string; }
+>   : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>foobar : { type: "foo"; foo: number; } | { type: "bar"; bar: string; }
+>       : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>fb.type === "foo" : boolean
+>                  : ^^^^^^^
+>fb.type : "bar" | "foo"
+>        : ^^^^^^^^^^^^^
+>fb : { type: "foo"; foo: number; } | { type: "bar"; bar: string; }
+>   : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>type : "bar" | "foo"
+>     : ^^^^^^^^^^^^^
+>"foo" : "foo"
+>      : ^^^^^
+
+if (foobarPred(foobar)) {
+>foobarPred(foobar) : boolean
+>                   : ^^^^^^^
+>foobarPred : (fb: { type: "foo"; foo: number; } | { type: "bar"; bar: string; }) => fb is { type: "foo"; foo: number; }
+>           : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>foobar : { type: "foo"; foo: number; } | { type: "bar"; bar: string; }
+>       : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  foobar.foo;
+>foobar.foo : number
+>           : ^^^^^^
+>foobar : { type: "foo"; foo: number; }
+>       : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>foo : number
+>    : ^^^^^^
+}
+
diff --git a/tests/cases/compiler/inferTypePredicates.ts b/tests/cases/compiler/inferTypePredicates.ts
@@ -269,3 +269,13 @@ const noInferenceFromImpossibleRest = (...f: []) => typeof f === "undefined";
 function inferWithRest(x: string | null, ...f: ["a", "b"]) {
   return typeof x === 'string';
 }
+
+// https://github.com/microsoft/TypeScript/issues/57947
+declare const foobar:
+  | { type: "foo"; foo: number }
+  | { type: "bar"; bar: string };
+
+const foobarPred = (fb: typeof foobar) => fb.type === "foo";
+if (foobarPred(foobar)) {
+  foobar.foo;
+}