Reinstate constraint check for template literal types

src/compiler/checker.ts

@@ -18402,6 +18402,16 @@ namespace ts {
                         return result;
                     }
                 }
+                else if (source.flags & TypeFlags.TemplateLiteral) {
+                    if (!(target.flags & TypeFlags.TemplateLiteral)) {
+                        const baseConstraint = getBaseConstraintOfType(source);
+                        const constraint = baseConstraint && baseConstraint !== source ? baseConstraint : stringType;
+                        if (result = isRelatedTo(constraint, target, reportErrors)) {
+                            resetErrorInfo(saveErrorInfo);
+                            return result;
+                        }
+                    }
+                }
                 else if (source.flags & TypeFlags.StringMapping) {
                     if (target.flags & TypeFlags.StringMapping && (<StringMappingType>source).symbol === (<StringMappingType>target).symbol) {
                         if (result = isRelatedTo((<StringMappingType>source).type, (<StringMappingType>target).type, reportErrors)) {

tests/baselines/reference/templateLiteralTypes3.errors.txt

@@ -126,4 +126,16 @@ tests/cases/conformance/types/literal/templateLiteralTypes3.ts(74,5): error TS23
 
     const value2 = "abc";
     const templated2: Templated = `${value2} abc` as const;
+
+    // Repro from #43620
+
+    type Prefixes = "foo" | "bar";
+
+    type AllPrefixData = "foo:baz" | "bar:baz";
+
+    type PrefixData<P extends Prefixes> = `${P}:baz`;
+
+    interface ITest<P extends Prefixes, E extends AllPrefixData = PrefixData<P>> {
+        blah: string;
+    }
 

tests/baselines/reference/templateLiteralTypes3.js

@@ -104,6 +104,18 @@ const templated1: Templated = `${value1} abc` as const;
 
 const value2 = "abc";
 const templated2: Templated = `${value2} abc` as const;
+
+// Repro from #43620
+
+type Prefixes = "foo" | "bar";
+
+type AllPrefixData = "foo:baz" | "bar:baz";
+
+type PrefixData<P extends Prefixes> = `${P}:baz`;
+
+interface ITest<P extends Prefixes, E extends AllPrefixData = PrefixData<P>> {
+    blah: string;
+}
 
 
 //// [templateLiteralTypes3.js]
@@ -198,3 +210,9 @@ declare const value1: string;
 declare const templated1: Templated;
 declare const value2 = "abc";
 declare const templated2: Templated;
+declare type Prefixes = "foo" | "bar";
+declare type AllPrefixData = "foo:baz" | "bar:baz";
+declare type PrefixData<P extends Prefixes> = `${P}:baz`;
+interface ITest<P extends Prefixes, E extends AllPrefixData = PrefixData<P>> {
+    blah: string;
+}

tests/baselines/reference/templateLiteralTypes3.symbols

@@ -342,3 +342,30 @@ const templated2: Templated = `${value2} abc` as const;
 >Templated : Symbol(Templated, Decl(templateLiteralTypes3.ts, 93, 29))
 >value2 : Symbol(value2, Decl(templateLiteralTypes3.ts, 103, 5))
 
+// Repro from #43620
+
+type Prefixes = "foo" | "bar";
+>Prefixes : Symbol(Prefixes, Decl(templateLiteralTypes3.ts, 104, 55))
+
+type AllPrefixData = "foo:baz" | "bar:baz";
+>AllPrefixData : Symbol(AllPrefixData, Decl(templateLiteralTypes3.ts, 108, 30))
+
+type PrefixData<P extends Prefixes> = `${P}:baz`;
+>PrefixData : Symbol(PrefixData, Decl(templateLiteralTypes3.ts, 110, 43))
+>P : Symbol(P, Decl(templateLiteralTypes3.ts, 112, 16))
+>Prefixes : Symbol(Prefixes, Decl(templateLiteralTypes3.ts, 104, 55))
+>P : Symbol(P, Decl(templateLiteralTypes3.ts, 112, 16))
+
+interface ITest<P extends Prefixes, E extends AllPrefixData = PrefixData<P>> {
+>ITest : Symbol(ITest, Decl(templateLiteralTypes3.ts, 112, 49))
+>P : Symbol(P, Decl(templateLiteralTypes3.ts, 114, 16))
+>Prefixes : Symbol(Prefixes, Decl(templateLiteralTypes3.ts, 104, 55))
+>E : Symbol(E, Decl(templateLiteralTypes3.ts, 114, 35))
+>AllPrefixData : Symbol(AllPrefixData, Decl(templateLiteralTypes3.ts, 108, 30))
+>PrefixData : Symbol(PrefixData, Decl(templateLiteralTypes3.ts, 110, 43))
+>P : Symbol(P, Decl(templateLiteralTypes3.ts, 114, 16))
+
+    blah: string;
+>blah : Symbol(ITest.blah, Decl(templateLiteralTypes3.ts, 114, 78))
+}
+

tests/baselines/reference/templateLiteralTypes3.types

@@ -363,3 +363,19 @@ const templated2: Templated = `${value2} abc` as const;
 >`${value2} abc` : "abc abc"
 >value2 : "abc"
 
+// Repro from #43620
+
+type Prefixes = "foo" | "bar";
+>Prefixes : Prefixes
+
+type AllPrefixData = "foo:baz" | "bar:baz";
+>AllPrefixData : AllPrefixData
+
+type PrefixData<P extends Prefixes> = `${P}:baz`;
+>PrefixData : `${P}:baz`
+
+interface ITest<P extends Prefixes, E extends AllPrefixData = PrefixData<P>> {
+    blah: string;
+>blah : string
+}
+

tests/cases/conformance/types/literal/templateLiteralTypes3.ts

@@ -106,3 +106,15 @@ const templated1: Templated = `${value1} abc` as const;
 
 const value2 = "abc";
 const templated2: Templated = `${value2} abc` as const;
+
+// Repro from #43620
+
+type Prefixes = "foo" | "bar";
+
+type AllPrefixData = "foo:baz" | "bar:baz";
+
+type PrefixData<P extends Prefixes> = `${P}:baz`;
+
+interface ITest<P extends Prefixes, E extends AllPrefixData = PrefixData<P>> {
+    blah: string;
+}