Stricter criteria for eliminating types in unions during inference

src/compiler/checker.ts

@@ -15486,8 +15486,7 @@ namespace ts {
             let visited: Map<number>;
             let bivariant = false;
             let propagationType: Type;
-            let inferenceMatch = false;
-            let inferenceIncomplete = false;
+            let inferencePriority = InferencePriority.MaxValue;
             let allowComplexConstraintInference = true;
             inferFromTypes(originalSource, originalTarget);
 
@@ -15600,7 +15599,7 @@ namespace ts {
                                 clearCachedInferences(inferences);
                             }
                         }
-                        inferenceMatch = true;
+                        inferencePriority = Math.min(inferencePriority, priority);
                         return;
                     }
                     else {
@@ -15694,19 +15693,15 @@ namespace ts {
                 const key = source.id + "," + target.id;
                 const status = visited && visited.get(key);
                 if (status !== undefined) {
-                    if (status & 1) inferenceMatch = true;
-                    if (status & 2) inferenceIncomplete = true;
+                    inferencePriority = Math.min(inferencePriority, status);
                     return;
                 }
-                (visited || (visited = createMap<number>())).set(key, 0);
-                const saveInferenceMatch = inferenceMatch;
-                const saveInferenceIncomplete = inferenceIncomplete;
-                inferenceMatch = false;
-                inferenceIncomplete = false;
+                (visited || (visited = createMap<number>())).set(key, InferencePriority.Circularity);
+                const saveInferencePriority = inferencePriority;
+                inferencePriority = InferencePriority.MaxValue;
                 action(source, target);
-                visited.set(key, (inferenceMatch ? 1 : 0) | (inferenceIncomplete ? 2 : 0));
-                inferenceMatch = inferenceMatch || saveInferenceMatch;
-                inferenceIncomplete = inferenceIncomplete || saveInferenceIncomplete;
+                visited.set(key, inferencePriority);
+                inferencePriority = Math.min(inferencePriority, saveInferencePriority);
             }
 
             function inferFromMatchingType(source: Type, targets: Type[], matches: (s: Type, t: Type) => boolean) {
@@ -15778,31 +15773,32 @@ namespace ts {
                     let nakedTypeVariable: Type | undefined;
                     const sources = source.flags & TypeFlags.Union ? (<UnionType>source).types : [source];
                     const matched = new Array<boolean>(sources.length);
-                    const saveInferenceIncomplete = inferenceIncomplete;
-                    inferenceIncomplete = false;
+                    let inferenceCircularity = false;
                     // First infer to types that are not naked type variables. For each source type we
-                    // track whether inferences were made from that particular type to some target.
+                    // track whether inferences were made from that particular type to some target with
+                    // equal priority (i.e. of equal quality) to what we would infer for a naked type
+                    // parameter.
                     for (const t of targets) {
                         if (getInferenceInfoForType(t)) {
                             nakedTypeVariable = t;
                             typeVariableCount++;
                         }
                         else {
                             for (let i = 0; i < sources.length; i++) {
-                                const saveInferenceMatch = inferenceMatch;
-                                inferenceMatch = false;
+                                const saveInferencePriority = inferencePriority;
+                                inferencePriority = InferencePriority.MaxValue;
                                 inferFromTypes(sources[i], t);
-                                if (inferenceMatch) matched[i] = true;
-                                inferenceMatch = inferenceMatch || saveInferenceMatch;
+                                if (inferencePriority === priority) matched[i] = true;
+                                inferenceCircularity = inferenceCircularity || inferencePriority === InferencePriority.Circularity;
+                                inferencePriority = Math.min(inferencePriority, saveInferencePriority);
                             }
                         }
                     }
-                    const inferenceComplete = !inferenceIncomplete;
-                    inferenceIncomplete = inferenceIncomplete || saveInferenceIncomplete;
-                    // If the target has a single naked type variable and inference completed (meaning we
-                    // explored the types fully), create a union of the source types from which no inferences
-                    // have been made so far and infer from that union to the naked type variable.
-                    if (typeVariableCount === 1 && inferenceComplete) {
+                    // If the target has a single naked type variable and no inference circularities were
+                    // encountered above (meaning we explored the types fully), create a union of the source
+                    // types from which no inferences have been made so far and infer from that union to the
+                    // naked type variable.
+                    if (typeVariableCount === 1 && !inferenceCircularity) {
                         const unmatched = flatMap(sources, (s, i) => matched[i] ? undefined : s);
                         if (unmatched.length) {
                             inferFromTypes(getUnionType(unmatched), nakedTypeVariable!);
@@ -15905,7 +15901,7 @@ namespace ts {
                 const symbol = isNonConstructorObject ? target.symbol : undefined;
                 if (symbol) {
                     if (contains(symbolStack, symbol)) {
-                        inferenceIncomplete = true;
+                        inferencePriority = InferencePriority.Circularity;
                         return;
                     }
                     (symbolStack || (symbolStack = [])).push(symbol);

src/compiler/types.ts

@@ -4471,8 +4471,10 @@ namespace ts {
         LiteralKeyof                 = 1 << 5,  // Inference made from a string literal to a keyof T
         NoConstraints                = 1 << 6,  // Don't infer from constraints of instantiable types
         AlwaysStrict                 = 1 << 7,  // Always use strict rules for contravariant inferences
+        MaxValue                     = 1 << 8,  // Seed for inference priority tracking
 
         PriorityImpliesCombination = ReturnType | MappedTypeConstraint | LiteralKeyof,  // These priorities imply that the resulting type should be a combination of all candidates
+        Circularity = -1,  // Inference circularity (value less than all other priorities)
     }
 
     /* @internal */

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2438,7 +2438,9 @@ declare namespace ts {
         LiteralKeyof = 32,
         NoConstraints = 64,
         AlwaysStrict = 128,
-        PriorityImpliesCombination = 56
+        MaxValue = 256,
+        PriorityImpliesCombination = 56,
+        Circularity = -1
     }
     /** @deprecated Use FileExtensionInfo instead. */
     export type JsFileExtensionInfo = FileExtensionInfo;

tests/baselines/reference/api/typescript.d.ts

@@ -2438,7 +2438,9 @@ declare namespace ts {
         LiteralKeyof = 32,
         NoConstraints = 64,
         AlwaysStrict = 128,
-        PriorityImpliesCombination = 56
+        MaxValue = 256,
+        PriorityImpliesCombination = 56,
+        Circularity = -1
     }
     /** @deprecated Use FileExtensionInfo instead. */
     export type JsFileExtensionInfo = FileExtensionInfo;

tests/baselines/reference/unionTypeInference.errors.txt

@@ -58,4 +58,30 @@ tests/cases/conformance/types/typeRelationships/typeInference/unionTypeInference
 
     declare function bar<T>(x: T, y: string | T): T;
     const y = bar(1, 2);
+
+    // Repro from #32752
+
+    const containsPromises: unique symbol = Symbol();
+
+    type DeepPromised<T> =
+        { [containsPromises]?: true } &
+        { [TKey in keyof T]: T[TKey] | DeepPromised<T[TKey]> | Promise<DeepPromised<T[TKey]>> };
+
+    async function fun<T>(deepPromised: DeepPromised<T>) {
+        const deepPromisedWithIndexer: DeepPromised<{ [name: string]: {} | null | undefined }> = deepPromised;
+        for (const value of Object.values(deepPromisedWithIndexer)) {
+            const awaitedValue = await value;
+            if (awaitedValue)
+                await fun(awaitedValue);
+        }
+    }
+
+    // Repro from #32752
+
+    type Deep<T> = { [K in keyof T]: T[K] | Deep<T[K]> };
+
+    declare function baz<T>(dp: Deep<T>): T;
+    declare let xx: { a: string | undefined };
+
+    baz(xx);
 

tests/baselines/reference/unionTypeInference.js

@@ -50,29 +50,64 @@ foo(x);
 
 declare function bar<T>(x: T, y: string | T): T;
 const y = bar(1, 2);
+
+// Repro from #32752
+
+const containsPromises: unique symbol = Symbol();
+
+type DeepPromised<T> =
+    { [containsPromises]?: true } &
+    { [TKey in keyof T]: T[TKey] | DeepPromised<T[TKey]> | Promise<DeepPromised<T[TKey]>> };
+
+async function fun<T>(deepPromised: DeepPromised<T>) {
+    const deepPromisedWithIndexer: DeepPromised<{ [name: string]: {} | null | undefined }> = deepPromised;
+    for (const value of Object.values(deepPromisedWithIndexer)) {
+        const awaitedValue = await value;
+        if (awaitedValue)
+            await fun(awaitedValue);
+    }
+}
+
+// Repro from #32752
+
+type Deep<T> = { [K in keyof T]: T[K] | Deep<T[K]> };
+
+declare function baz<T>(dp: Deep<T>): T;
+declare let xx: { a: string | undefined };
+
+baz(xx);
 
 
 //// [unionTypeInference.js]
-"use strict";
-exports.__esModule = true;
-var a1 = f1(1, 2); // 1 | 2
-var a2 = f1(1, "hello"); // 1
-var a3 = f1(1, sn); // number
-var a4 = f1(undefined, "abc"); // undefined
-var a5 = f1("foo", "bar"); // "foo"
-var a6 = f1(true, false); // boolean
-var a7 = f1("hello", 1); // Error
+const a1 = f1(1, 2); // 1 | 2
+const a2 = f1(1, "hello"); // 1
+const a3 = f1(1, sn); // number
+const a4 = f1(undefined, "abc"); // undefined
+const a5 = f1("foo", "bar"); // "foo"
+const a6 = f1(true, false); // boolean
+const a7 = f1("hello", 1); // Error
 var b1 = f2(["string", true]); // boolean
-var c1 = f3(5); // 5
-var c2 = f3(sn); // number
-var c3 = f3(true); // true
-var c4 = f3(b); // true
-var c5 = f3("abc"); // never
-var d1 = f4("abc");
-var d2 = f4(s);
-var d3 = f4(42); // Error
+const c1 = f3(5); // 5
+const c2 = f3(sn); // number
+const c3 = f3(true); // true
+const c4 = f3(b); // true
+const c5 = f3("abc"); // never
+const d1 = f4("abc");
+const d2 = f4(s);
+const d3 = f4(42); // Error
 function qux(p1, p2) {
     p1 = p2;
 }
 foo(x);
-var y = bar(1, 2);
+const y = bar(1, 2);
+// Repro from #32752
+const containsPromises = Symbol();
+async function fun(deepPromised) {
+    const deepPromisedWithIndexer = deepPromised;
+    for (const value of Object.values(deepPromisedWithIndexer)) {
+        const awaitedValue = await value;
+        if (awaitedValue)
+            await fun(awaitedValue);
+    }
+}
+baz(xx);

tests/baselines/reference/unionTypeInference.symbols

@@ -163,12 +163,12 @@ declare function foo<T>(x: T | Promise<T>): void;
 >T : Symbol(T, Decl(unionTypeInference.ts, 45, 21))
 >x : Symbol(x, Decl(unionTypeInference.ts, 45, 24))
 >T : Symbol(T, Decl(unionTypeInference.ts, 45, 21))
->Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2018.promise.d.ts, --, --))
 >T : Symbol(T, Decl(unionTypeInference.ts, 45, 21))
 
 declare let x: false | Promise<true>;
 >x : Symbol(x, Decl(unionTypeInference.ts, 46, 11))
->Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2018.promise.d.ts, --, --))
 
 foo(x);
 >foo : Symbol(foo, Decl(unionTypeInference.ts, 41, 1))
@@ -187,3 +187,92 @@ const y = bar(1, 2);
 >y : Symbol(y, Decl(unionTypeInference.ts, 50, 5))
 >bar : Symbol(bar, Decl(unionTypeInference.ts, 47, 7))
 
+// Repro from #32752
+
+const containsPromises: unique symbol = Symbol();
+>containsPromises : Symbol(containsPromises, Decl(unionTypeInference.ts, 54, 5))
+>Symbol : Symbol(Symbol, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.symbol.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2019.symbol.d.ts, --, --))
+
+type DeepPromised<T> =
+>DeepPromised : Symbol(DeepPromised, Decl(unionTypeInference.ts, 54, 49))
+>T : Symbol(T, Decl(unionTypeInference.ts, 56, 18))
+
+    { [containsPromises]?: true } &
+>[containsPromises] : Symbol([containsPromises], Decl(unionTypeInference.ts, 57, 5))
+>containsPromises : Symbol(containsPromises, Decl(unionTypeInference.ts, 54, 5))
+
+    { [TKey in keyof T]: T[TKey] | DeepPromised<T[TKey]> | Promise<DeepPromised<T[TKey]>> };
+>TKey : Symbol(TKey, Decl(unionTypeInference.ts, 58, 7))
+>T : Symbol(T, Decl(unionTypeInference.ts, 56, 18))
+>T : Symbol(T, Decl(unionTypeInference.ts, 56, 18))
+>TKey : Symbol(TKey, Decl(unionTypeInference.ts, 58, 7))
+>DeepPromised : Symbol(DeepPromised, Decl(unionTypeInference.ts, 54, 49))
+>T : Symbol(T, Decl(unionTypeInference.ts, 56, 18))
+>TKey : Symbol(TKey, Decl(unionTypeInference.ts, 58, 7))
+>Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.promise.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --), Decl(lib.es2018.promise.d.ts, --, --))
+>DeepPromised : Symbol(DeepPromised, Decl(unionTypeInference.ts, 54, 49))
+>T : Symbol(T, Decl(unionTypeInference.ts, 56, 18))
+>TKey : Symbol(TKey, Decl(unionTypeInference.ts, 58, 7))
+
+async function fun<T>(deepPromised: DeepPromised<T>) {
+>fun : Symbol(fun, Decl(unionTypeInference.ts, 58, 92))
+>T : Symbol(T, Decl(unionTypeInference.ts, 60, 19))
+>deepPromised : Symbol(deepPromised, Decl(unionTypeInference.ts, 60, 22))
+>DeepPromised : Symbol(DeepPromised, Decl(unionTypeInference.ts, 54, 49))
+>T : Symbol(T, Decl(unionTypeInference.ts, 60, 19))
+
+    const deepPromisedWithIndexer: DeepPromised<{ [name: string]: {} | null | undefined }> = deepPromised;
+>deepPromisedWithIndexer : Symbol(deepPromisedWithIndexer, Decl(unionTypeInference.ts, 61, 9))
+>DeepPromised : Symbol(DeepPromised, Decl(unionTypeInference.ts, 54, 49))
+>name : Symbol(name, Decl(unionTypeInference.ts, 61, 51))
+>deepPromised : Symbol(deepPromised, Decl(unionTypeInference.ts, 60, 22))
+
+    for (const value of Object.values(deepPromisedWithIndexer)) {
+>value : Symbol(value, Decl(unionTypeInference.ts, 62, 14))
+>Object.values : Symbol(ObjectConstructor.values, Decl(lib.es2017.object.d.ts, --, --), Decl(lib.es2017.object.d.ts, --, --))
+>Object : Symbol(Object, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>values : Symbol(ObjectConstructor.values, Decl(lib.es2017.object.d.ts, --, --), Decl(lib.es2017.object.d.ts, --, --))
+>deepPromisedWithIndexer : Symbol(deepPromisedWithIndexer, Decl(unionTypeInference.ts, 61, 9))
+
+        const awaitedValue = await value;
+>awaitedValue : Symbol(awaitedValue, Decl(unionTypeInference.ts, 63, 13))
+>value : Symbol(value, Decl(unionTypeInference.ts, 62, 14))
+
+        if (awaitedValue)
+>awaitedValue : Symbol(awaitedValue, Decl(unionTypeInference.ts, 63, 13))
+
+            await fun(awaitedValue);
+>fun : Symbol(fun, Decl(unionTypeInference.ts, 58, 92))
+>awaitedValue : Symbol(awaitedValue, Decl(unionTypeInference.ts, 63, 13))
+    }
+}
+
+// Repro from #32752
+
+type Deep<T> = { [K in keyof T]: T[K] | Deep<T[K]> };
+>Deep : Symbol(Deep, Decl(unionTypeInference.ts, 67, 1))
+>T : Symbol(T, Decl(unionTypeInference.ts, 71, 10))
+>K : Symbol(K, Decl(unionTypeInference.ts, 71, 18))
+>T : Symbol(T, Decl(unionTypeInference.ts, 71, 10))
+>T : Symbol(T, Decl(unionTypeInference.ts, 71, 10))
+>K : Symbol(K, Decl(unionTypeInference.ts, 71, 18))
+>Deep : Symbol(Deep, Decl(unionTypeInference.ts, 67, 1))
+>T : Symbol(T, Decl(unionTypeInference.ts, 71, 10))
+>K : Symbol(K, Decl(unionTypeInference.ts, 71, 18))
+
+declare function baz<T>(dp: Deep<T>): T;
+>baz : Symbol(baz, Decl(unionTypeInference.ts, 71, 53))
+>T : Symbol(T, Decl(unionTypeInference.ts, 73, 21))
+>dp : Symbol(dp, Decl(unionTypeInference.ts, 73, 24))
+>Deep : Symbol(Deep, Decl(unionTypeInference.ts, 67, 1))
+>T : Symbol(T, Decl(unionTypeInference.ts, 73, 21))
+>T : Symbol(T, Decl(unionTypeInference.ts, 73, 21))
+
+declare let xx: { a: string | undefined };
+>xx : Symbol(xx, Decl(unionTypeInference.ts, 74, 11))
+>a : Symbol(a, Decl(unionTypeInference.ts, 74, 17))
+
+baz(xx);
+>baz : Symbol(baz, Decl(unionTypeInference.ts, 71, 53))
+>xx : Symbol(xx, Decl(unionTypeInference.ts, 74, 11))
+