Consistent inferences when inferring to template literal type (#40518)

* Consistently make inferences when inferring to template literal type * Add tests * Accept new baselines
2025-11-18 17:21:48 +00:00 · 2020-09-12 16:33:33 -10:00
parent c9422e6aa1
commit 57c8938d9e
6 changed files with 209 additions and 137 deletions
@@ -20056,14 +20056,12 @@ namespace ts {
            }

            function inferToTemplateLiteralType(source: Type, target: TemplateLiteralType) {
-                if (source.flags & (TypeFlags.StringLike | TypeFlags.Index)) {
-                    const matches = source.flags & TypeFlags.StringLiteral ? inferLiteralsFromTemplateLiteralType(<StringLiteralType>source, target) :
-                        source.flags & TypeFlags.TemplateLiteral && arraysEqual((<TemplateLiteralType>source).texts, target.texts) && arraysEqual((<TemplateLiteralType>source).casings, target.casings)? (<TemplateLiteralType>source).types :
-                        undefined;
-                    const types = target.types;
-                    for (let i = 0; i < types.length; i++) {
-                        inferFromTypes(matches ? matches[i] : source.flags & TypeFlags.StringLiteral ? neverType : stringType, types[i]);
-                    }
+                const matches = source.flags & TypeFlags.StringLiteral ? inferLiteralsFromTemplateLiteralType(<StringLiteralType>source, target) :
+                    source.flags & TypeFlags.TemplateLiteral && arraysEqual((<TemplateLiteralType>source).texts, target.texts) && arraysEqual((<TemplateLiteralType>source).casings, target.casings)? (<TemplateLiteralType>source).types :
+                    undefined;
+                const types = target.types;
+                for (let i = 0; i < types.length; i++) {
+                    inferFromTypes(matches ? matches[i] : neverType, types[i]);
                }
            }

@@ -5,9 +5,9 @@ tests/cases/conformance/types/literal/templateLiteralTypes1.ts(39,5): error TS23
      Type 'string' is not assignable to type 'B'.
        'string' is assignable to the constraint of type 'B', but 'B' could be instantiated with a different subtype of constraint 'string'.
 tests/cases/conformance/types/literal/templateLiteralTypes1.ts(165,15): error TS1338: 'infer' declarations are only permitted in the 'extends' clause of a conditional type.
-tests/cases/conformance/types/literal/templateLiteralTypes1.ts(188,16): error TS2590: Expression produces a union type that is too complex to represent.
-tests/cases/conformance/types/literal/templateLiteralTypes1.ts(192,16): error TS2590: Expression produces a union type that is too complex to represent.
-tests/cases/conformance/types/literal/templateLiteralTypes1.ts(196,16): error TS2590: Expression produces a union type that is too complex to represent.
+tests/cases/conformance/types/literal/templateLiteralTypes1.ts(197,16): error TS2590: Expression produces a union type that is too complex to represent.
+tests/cases/conformance/types/literal/templateLiteralTypes1.ts(201,16): error TS2590: Expression produces a union type that is too complex to represent.
+tests/cases/conformance/types/literal/templateLiteralTypes1.ts(205,16): error TS2590: Expression produces a union type that is too complex to represent.


 ==== tests/cases/conformance/types/literal/templateLiteralTypes1.ts (6 errors) ====
@@ -198,6 +198,15 @@ tests/cases/conformance/types/literal/templateLiteralTypes1.ts(196,16): error TS
    
    type L1 = Chars<'FooBarBazThisIsALongerString'>;  // ['F', 'o', 'o', 'B', 'a', 'r', ...]
    
+    // Infer never when source isn't a literal type that matches the pattern
+    
+    type Foo<T> = T extends `*${infer S}*` ? S : never;
+    
+    type TF1 = Foo<any>;      // never
+    type TF2 = Foo<string>;   // never
+    type TF3 = Foo<'abc'>;    // never
+    type TF4 = Foo<'*abc*'>;  // 'abc'
+    
    // Cross product unions limited to 100,000 constituents
    
    type A = any;
@@ -176,6 +176,15 @@ type Chars<S extends string> =

 type L1 = Chars<'FooBarBazThisIsALongerString'>;  // ['F', 'o', 'o', 'B', 'a', 'r', ...]

+// Infer never when source isn't a literal type that matches the pattern
+
+type Foo<T> = T extends `*${infer S}*` ? S : never;
+
+type TF1 = Foo<any>;      // never
+type TF2 = Foo<string>;   // never
+type TF3 = Foo<'abc'>;    // never
+type TF4 = Foo<'*abc*'>;  // 'abc'
+
 // Cross product unions limited to 100,000 constituents

 type A = any;
@@ -329,6 +338,11 @@ declare type S2<S extends string> = S;
 declare type TV1 = `${infer X}`;
 declare type Chars<S extends string> = string extends S ? string[] : S extends `${infer C0}${infer C1}${infer C2}${infer C3}${infer C4}${infer C5}${infer C6}${infer C7}${infer C8}${infer C9}${infer R}` ? [C0, C1, C2, C3, C4, C5, C6, C7, C8, C9, ...Chars<R>] : S extends `${infer C}${infer R}` ? [C, ...Chars<R>] : S extends '' ? [] : never;
 declare type L1 = Chars<'FooBarBazThisIsALongerString'>;
+declare type Foo<T> = T extends `*${infer S}*` ? S : never;
+declare type TF1 = Foo<any>;
+declare type TF2 = Foo<string>;
+declare type TF3 = Foo<'abc'>;
+declare type TF4 = Foo<'*abc*'>;
 declare type A = any;
 declare type U1 = {
    a1: A;
@@ -667,153 +667,178 @@ type L1 = Chars<'FooBarBazThisIsALongerString'>;  // ['F', 'o', 'o', 'B', 'a', '
 >L1 : Symbol(L1, Decl(templateLiteralTypes1.ts, 173, 10))
 >Chars : Symbol(Chars, Decl(templateLiteralTypes1.ts, 164, 24))

+// Infer never when source isn't a literal type that matches the pattern
+
+type Foo<T> = T extends `*${infer S}*` ? S : never;
+>Foo : Symbol(Foo, Decl(templateLiteralTypes1.ts, 175, 48))
+>T : Symbol(T, Decl(templateLiteralTypes1.ts, 179, 9))
+>T : Symbol(T, Decl(templateLiteralTypes1.ts, 179, 9))
+>S : Symbol(S, Decl(templateLiteralTypes1.ts, 179, 33))
+>S : Symbol(S, Decl(templateLiteralTypes1.ts, 179, 33))
+
+type TF1 = Foo<any>;      // never
+>TF1 : Symbol(TF1, Decl(templateLiteralTypes1.ts, 179, 51))
+>Foo : Symbol(Foo, Decl(templateLiteralTypes1.ts, 175, 48))
+
+type TF2 = Foo<string>;   // never
+>TF2 : Symbol(TF2, Decl(templateLiteralTypes1.ts, 181, 20))
+>Foo : Symbol(Foo, Decl(templateLiteralTypes1.ts, 175, 48))
+
+type TF3 = Foo<'abc'>;    // never
+>TF3 : Symbol(TF3, Decl(templateLiteralTypes1.ts, 182, 23))
+>Foo : Symbol(Foo, Decl(templateLiteralTypes1.ts, 175, 48))
+
+type TF4 = Foo<'*abc*'>;  // 'abc'
+>TF4 : Symbol(TF4, Decl(templateLiteralTypes1.ts, 183, 22))
+>Foo : Symbol(Foo, Decl(templateLiteralTypes1.ts, 175, 48))
+
 // Cross product unions limited to 100,000 constituents

 type A = any;
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))

 type U1 = {a1:A} | {b1:A} | {c1:A} | {d1:A} | {e1:A} | {f1:A} | {g1:A} | {h1:A} | {i1:A} | {j1:A};
->U1 : Symbol(U1, Decl(templateLiteralTypes1.ts, 179, 13))
->a1 : Symbol(a1, Decl(templateLiteralTypes1.ts, 181, 11))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->b1 : Symbol(b1, Decl(templateLiteralTypes1.ts, 181, 20))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->c1 : Symbol(c1, Decl(templateLiteralTypes1.ts, 181, 29))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->d1 : Symbol(d1, Decl(templateLiteralTypes1.ts, 181, 38))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->e1 : Symbol(e1, Decl(templateLiteralTypes1.ts, 181, 47))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->f1 : Symbol(f1, Decl(templateLiteralTypes1.ts, 181, 56))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->g1 : Symbol(g1, Decl(templateLiteralTypes1.ts, 181, 65))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->h1 : Symbol(h1, Decl(templateLiteralTypes1.ts, 181, 74))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->i1 : Symbol(i1, Decl(templateLiteralTypes1.ts, 181, 83))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->j1 : Symbol(j1, Decl(templateLiteralTypes1.ts, 181, 92))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
+>U1 : Symbol(U1, Decl(templateLiteralTypes1.ts, 188, 13))
+>a1 : Symbol(a1, Decl(templateLiteralTypes1.ts, 190, 11))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>b1 : Symbol(b1, Decl(templateLiteralTypes1.ts, 190, 20))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>c1 : Symbol(c1, Decl(templateLiteralTypes1.ts, 190, 29))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>d1 : Symbol(d1, Decl(templateLiteralTypes1.ts, 190, 38))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>e1 : Symbol(e1, Decl(templateLiteralTypes1.ts, 190, 47))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>f1 : Symbol(f1, Decl(templateLiteralTypes1.ts, 190, 56))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>g1 : Symbol(g1, Decl(templateLiteralTypes1.ts, 190, 65))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>h1 : Symbol(h1, Decl(templateLiteralTypes1.ts, 190, 74))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>i1 : Symbol(i1, Decl(templateLiteralTypes1.ts, 190, 83))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>j1 : Symbol(j1, Decl(templateLiteralTypes1.ts, 190, 92))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))

 type U2 = {a2:A} | {b2:A} | {c2:A} | {d2:A} | {e2:A} | {f2:A} | {g2:A} | {h2:A} | {i2:A} | {j2:A};
->U2 : Symbol(U2, Decl(templateLiteralTypes1.ts, 181, 98))
->a2 : Symbol(a2, Decl(templateLiteralTypes1.ts, 182, 11))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->b2 : Symbol(b2, Decl(templateLiteralTypes1.ts, 182, 20))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->c2 : Symbol(c2, Decl(templateLiteralTypes1.ts, 182, 29))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->d2 : Symbol(d2, Decl(templateLiteralTypes1.ts, 182, 38))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->e2 : Symbol(e2, Decl(templateLiteralTypes1.ts, 182, 47))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->f2 : Symbol(f2, Decl(templateLiteralTypes1.ts, 182, 56))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->g2 : Symbol(g2, Decl(templateLiteralTypes1.ts, 182, 65))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->h2 : Symbol(h2, Decl(templateLiteralTypes1.ts, 182, 74))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->i2 : Symbol(i2, Decl(templateLiteralTypes1.ts, 182, 83))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->j2 : Symbol(j2, Decl(templateLiteralTypes1.ts, 182, 92))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
+>U2 : Symbol(U2, Decl(templateLiteralTypes1.ts, 190, 98))
+>a2 : Symbol(a2, Decl(templateLiteralTypes1.ts, 191, 11))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>b2 : Symbol(b2, Decl(templateLiteralTypes1.ts, 191, 20))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>c2 : Symbol(c2, Decl(templateLiteralTypes1.ts, 191, 29))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>d2 : Symbol(d2, Decl(templateLiteralTypes1.ts, 191, 38))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>e2 : Symbol(e2, Decl(templateLiteralTypes1.ts, 191, 47))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>f2 : Symbol(f2, Decl(templateLiteralTypes1.ts, 191, 56))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>g2 : Symbol(g2, Decl(templateLiteralTypes1.ts, 191, 65))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>h2 : Symbol(h2, Decl(templateLiteralTypes1.ts, 191, 74))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>i2 : Symbol(i2, Decl(templateLiteralTypes1.ts, 191, 83))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>j2 : Symbol(j2, Decl(templateLiteralTypes1.ts, 191, 92))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))

 type U3 = {a3:A} | {b3:A} | {c3:A} | {d3:A} | {e3:A} | {f3:A} | {g3:A} | {h3:A} | {i3:A} | {j3:A};
->U3 : Symbol(U3, Decl(templateLiteralTypes1.ts, 182, 98))
->a3 : Symbol(a3, Decl(templateLiteralTypes1.ts, 183, 11))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->b3 : Symbol(b3, Decl(templateLiteralTypes1.ts, 183, 20))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->c3 : Symbol(c3, Decl(templateLiteralTypes1.ts, 183, 29))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->d3 : Symbol(d3, Decl(templateLiteralTypes1.ts, 183, 38))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->e3 : Symbol(e3, Decl(templateLiteralTypes1.ts, 183, 47))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->f3 : Symbol(f3, Decl(templateLiteralTypes1.ts, 183, 56))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->g3 : Symbol(g3, Decl(templateLiteralTypes1.ts, 183, 65))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->h3 : Symbol(h3, Decl(templateLiteralTypes1.ts, 183, 74))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->i3 : Symbol(i3, Decl(templateLiteralTypes1.ts, 183, 83))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->j3 : Symbol(j3, Decl(templateLiteralTypes1.ts, 183, 92))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
+>U3 : Symbol(U3, Decl(templateLiteralTypes1.ts, 191, 98))
+>a3 : Symbol(a3, Decl(templateLiteralTypes1.ts, 192, 11))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>b3 : Symbol(b3, Decl(templateLiteralTypes1.ts, 192, 20))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>c3 : Symbol(c3, Decl(templateLiteralTypes1.ts, 192, 29))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>d3 : Symbol(d3, Decl(templateLiteralTypes1.ts, 192, 38))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>e3 : Symbol(e3, Decl(templateLiteralTypes1.ts, 192, 47))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>f3 : Symbol(f3, Decl(templateLiteralTypes1.ts, 192, 56))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>g3 : Symbol(g3, Decl(templateLiteralTypes1.ts, 192, 65))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>h3 : Symbol(h3, Decl(templateLiteralTypes1.ts, 192, 74))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>i3 : Symbol(i3, Decl(templateLiteralTypes1.ts, 192, 83))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>j3 : Symbol(j3, Decl(templateLiteralTypes1.ts, 192, 92))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))

 type U4 = {a4:A} | {b4:A} | {c4:A} | {d4:A} | {e4:A} | {f4:A} | {g4:A} | {h4:A} | {i4:A} | {j4:A};
->U4 : Symbol(U4, Decl(templateLiteralTypes1.ts, 183, 98))
->a4 : Symbol(a4, Decl(templateLiteralTypes1.ts, 184, 11))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->b4 : Symbol(b4, Decl(templateLiteralTypes1.ts, 184, 20))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->c4 : Symbol(c4, Decl(templateLiteralTypes1.ts, 184, 29))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->d4 : Symbol(d4, Decl(templateLiteralTypes1.ts, 184, 38))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->e4 : Symbol(e4, Decl(templateLiteralTypes1.ts, 184, 47))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->f4 : Symbol(f4, Decl(templateLiteralTypes1.ts, 184, 56))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->g4 : Symbol(g4, Decl(templateLiteralTypes1.ts, 184, 65))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->h4 : Symbol(h4, Decl(templateLiteralTypes1.ts, 184, 74))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->i4 : Symbol(i4, Decl(templateLiteralTypes1.ts, 184, 83))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->j4 : Symbol(j4, Decl(templateLiteralTypes1.ts, 184, 92))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
+>U4 : Symbol(U4, Decl(templateLiteralTypes1.ts, 192, 98))
+>a4 : Symbol(a4, Decl(templateLiteralTypes1.ts, 193, 11))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>b4 : Symbol(b4, Decl(templateLiteralTypes1.ts, 193, 20))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>c4 : Symbol(c4, Decl(templateLiteralTypes1.ts, 193, 29))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>d4 : Symbol(d4, Decl(templateLiteralTypes1.ts, 193, 38))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>e4 : Symbol(e4, Decl(templateLiteralTypes1.ts, 193, 47))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>f4 : Symbol(f4, Decl(templateLiteralTypes1.ts, 193, 56))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>g4 : Symbol(g4, Decl(templateLiteralTypes1.ts, 193, 65))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>h4 : Symbol(h4, Decl(templateLiteralTypes1.ts, 193, 74))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>i4 : Symbol(i4, Decl(templateLiteralTypes1.ts, 193, 83))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>j4 : Symbol(j4, Decl(templateLiteralTypes1.ts, 193, 92))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))

 type U5 = {a5:A} | {b5:A} | {c5:A} | {d5:A} | {e5:A} | {f5:A} | {g5:A} | {h5:A} | {i5:A} | {j5:A};
->U5 : Symbol(U5, Decl(templateLiteralTypes1.ts, 184, 98))
->a5 : Symbol(a5, Decl(templateLiteralTypes1.ts, 185, 11))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->b5 : Symbol(b5, Decl(templateLiteralTypes1.ts, 185, 20))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->c5 : Symbol(c5, Decl(templateLiteralTypes1.ts, 185, 29))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->d5 : Symbol(d5, Decl(templateLiteralTypes1.ts, 185, 38))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->e5 : Symbol(e5, Decl(templateLiteralTypes1.ts, 185, 47))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->f5 : Symbol(f5, Decl(templateLiteralTypes1.ts, 185, 56))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->g5 : Symbol(g5, Decl(templateLiteralTypes1.ts, 185, 65))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->h5 : Symbol(h5, Decl(templateLiteralTypes1.ts, 185, 74))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->i5 : Symbol(i5, Decl(templateLiteralTypes1.ts, 185, 83))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
->j5 : Symbol(j5, Decl(templateLiteralTypes1.ts, 185, 92))
->A : Symbol(A, Decl(templateLiteralTypes1.ts, 175, 48))
+>U5 : Symbol(U5, Decl(templateLiteralTypes1.ts, 193, 98))
+>a5 : Symbol(a5, Decl(templateLiteralTypes1.ts, 194, 11))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>b5 : Symbol(b5, Decl(templateLiteralTypes1.ts, 194, 20))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>c5 : Symbol(c5, Decl(templateLiteralTypes1.ts, 194, 29))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>d5 : Symbol(d5, Decl(templateLiteralTypes1.ts, 194, 38))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>e5 : Symbol(e5, Decl(templateLiteralTypes1.ts, 194, 47))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>f5 : Symbol(f5, Decl(templateLiteralTypes1.ts, 194, 56))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>g5 : Symbol(g5, Decl(templateLiteralTypes1.ts, 194, 65))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>h5 : Symbol(h5, Decl(templateLiteralTypes1.ts, 194, 74))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>i5 : Symbol(i5, Decl(templateLiteralTypes1.ts, 194, 83))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))
+>j5 : Symbol(j5, Decl(templateLiteralTypes1.ts, 194, 92))
+>A : Symbol(A, Decl(templateLiteralTypes1.ts, 184, 24))

 type U100000 = U1 & U2 & U3 & U4 & U5;  // Error
->U100000 : Symbol(U100000, Decl(templateLiteralTypes1.ts, 185, 98))
->U1 : Symbol(U1, Decl(templateLiteralTypes1.ts, 179, 13))
->U2 : Symbol(U2, Decl(templateLiteralTypes1.ts, 181, 98))
->U3 : Symbol(U3, Decl(templateLiteralTypes1.ts, 182, 98))
->U4 : Symbol(U4, Decl(templateLiteralTypes1.ts, 183, 98))
->U5 : Symbol(U5, Decl(templateLiteralTypes1.ts, 184, 98))
+>U100000 : Symbol(U100000, Decl(templateLiteralTypes1.ts, 194, 98))
+>U1 : Symbol(U1, Decl(templateLiteralTypes1.ts, 188, 13))
+>U2 : Symbol(U2, Decl(templateLiteralTypes1.ts, 190, 98))
+>U3 : Symbol(U3, Decl(templateLiteralTypes1.ts, 191, 98))
+>U4 : Symbol(U4, Decl(templateLiteralTypes1.ts, 192, 98))
+>U5 : Symbol(U5, Decl(templateLiteralTypes1.ts, 193, 98))

 type Digits = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9;
->Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 187, 38))
+>Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 196, 38))

 type D100000 = `${Digits}${Digits}${Digits}${Digits}${Digits}`;  // Error
->D100000 : Symbol(D100000, Decl(templateLiteralTypes1.ts, 189, 52))
->Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 187, 38))
->Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 187, 38))
->Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 187, 38))
->Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 187, 38))
->Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 187, 38))
+>D100000 : Symbol(D100000, Decl(templateLiteralTypes1.ts, 198, 52))
+>Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 196, 38))
+>Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 196, 38))
+>Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 196, 38))
+>Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 196, 38))
+>Digits : Symbol(Digits, Decl(templateLiteralTypes1.ts, 196, 38))

 type TDigits = [0] | [1] | [2] | [3] | [4] | [5] | [6] | [7] | [8] | [9];
->TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 191, 63))
+>TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 200, 63))

 type T100000 = [...TDigits, ...TDigits, ...TDigits, ...TDigits, ...TDigits];  // Error
->T100000 : Symbol(T100000, Decl(templateLiteralTypes1.ts, 193, 73))
->TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 191, 63))
->TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 191, 63))
->TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 191, 63))
->TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 191, 63))
->TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 191, 63))
+>T100000 : Symbol(T100000, Decl(templateLiteralTypes1.ts, 202, 73))
+>TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 200, 63))
+>TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 200, 63))
+>TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 200, 63))
+>TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 200, 63))
+>TDigits : Symbol(TDigits, Decl(templateLiteralTypes1.ts, 200, 63))

@@ -414,6 +414,23 @@ type Chars<S extends string> =
 type L1 = Chars<'FooBarBazThisIsALongerString'>;  // ['F', 'o', 'o', 'B', 'a', 'r', ...]
 >L1 : ["F", "o", "o", "B", "a", "r", "B", "a", "z", "T", "h", "i", "s", "I", "s", "A", "L", "o", "n", "g", "e", "r", "S", "t", "r", "i", "n", "g"]

+// Infer never when source isn't a literal type that matches the pattern
+
+type Foo<T> = T extends `*${infer S}*` ? S : never;
+>Foo : Foo<T>
+
+type TF1 = Foo<any>;      // never
+>TF1 : never
+
+type TF2 = Foo<string>;   // never
+>TF2 : never
+
+type TF3 = Foo<'abc'>;    // never
+>TF3 : never
+
+type TF4 = Foo<'*abc*'>;  // 'abc'
+>TF4 : "abc"
+
 // Cross product unions limited to 100,000 constituents

 type A = any;
@@ -178,6 +178,15 @@ type Chars<S extends string> =

 type L1 = Chars<'FooBarBazThisIsALongerString'>;  // ['F', 'o', 'o', 'B', 'a', 'r', ...]

+// Infer never when source isn't a literal type that matches the pattern
+
+type Foo<T> = T extends `*${infer S}*` ? S : never;
+
+type TF1 = Foo<any>;      // never
+type TF2 = Foo<string>;   // never
+type TF3 = Foo<'abc'>;    // never
+type TF4 = Foo<'*abc*'>;  // 'abc'
+
 // Cross product unions limited to 100,000 constituents

 type A = any;