Mapped symbol

src/compiler/checker.ts

@@ -9656,19 +9656,20 @@ namespace ts {
                 if (isTypeUsableAsPropertyName(t)) {
                     const propName = getPropertyNameFromType(t);
                     const modifiersProp = getPropertyOfType(modifiersType, propName);
+                    const templateProp = (templateType.flags & TypeFlags.IndexedAccess) && getPropertyOfType((<IndexedAccessType>templateType).objectType, propName);
                     const isOptional = !!(templateModifiers & MappedTypeModifiers.IncludeOptional ||
                         !(templateModifiers & MappedTypeModifiers.ExcludeOptional) && modifiersProp && modifiersProp.flags & SymbolFlags.Optional);
                     const isReadonly = !!(templateModifiers & MappedTypeModifiers.IncludeReadonly ||
                         !(templateModifiers & MappedTypeModifiers.ExcludeReadonly) && modifiersProp && isReadonlySymbol(modifiersProp));
                     const stripOptional = strictNullChecks && !isOptional && modifiersProp && modifiersProp.flags & SymbolFlags.Optional;
                     const prop = <MappedSymbol>createSymbol(SymbolFlags.Property | (isOptional ? SymbolFlags.Optional : 0), propName,
                         CheckFlags.Mapped | (isReadonly ? CheckFlags.Readonly : 0) | (stripOptional ? CheckFlags.StripOptional : 0));
+
                     prop.mappedType = type;
                     prop.mapper = templateMapper;
-                    if (modifiersProp) {
-                        prop.syntheticOrigin = modifiersProp;
-                        prop.declarations = modifiersProp.declarations;
-                    }
+
+                    prop.syntheticOrigin = templateProp || modifiersProp;
+                    prop.declarations = templateProp && templateProp.declarations || modifiersProp && modifiersProp.declarations || undefined!;
                     prop.nameType = t;
                     members.set(propName, prop);
                 }

tests/baselines/reference/mappedTypes7.js

@@ -0,0 +1,23 @@
+//// [mappedTypes7.ts]
+interface I {
+    a: number;
+    b: number;
+}
+type J = {
+    [K in 'b' | 'a']: I[K]
+};
+
+type L = Pick<J, 'a'>
+
+declare const j: J;
+j.a;
+j.b;
+
+declare const l: L
+l.a
+
+
+//// [mappedTypes7.js]
+j.a;
+j.b;
+l.a;

tests/baselines/reference/mappedTypes7.symbols

@@ -0,0 +1,48 @@
+=== tests/cases/conformance/types/mapped/mappedTypes7.ts ===
+interface I {
+>I : Symbol(I, Decl(mappedTypes7.ts, 0, 0))
+
+    a: number;
+>a : Symbol(I.a, Decl(mappedTypes7.ts, 0, 13))
+
+    b: number;
+>b : Symbol(I.b, Decl(mappedTypes7.ts, 1, 14))
+}
+type J = {
+>J : Symbol(J, Decl(mappedTypes7.ts, 3, 1))
+
+    [K in 'b' | 'a']: I[K]
+>K : Symbol(K, Decl(mappedTypes7.ts, 5, 5))
+>I : Symbol(I, Decl(mappedTypes7.ts, 0, 0))
+>K : Symbol(K, Decl(mappedTypes7.ts, 5, 5))
+
+};
+
+type L = Pick<J, 'a'>
+>L : Symbol(L, Decl(mappedTypes7.ts, 6, 2))
+>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
+>J : Symbol(J, Decl(mappedTypes7.ts, 3, 1))
+
+declare const j: J;
+>j : Symbol(j, Decl(mappedTypes7.ts, 10, 13))
+>J : Symbol(J, Decl(mappedTypes7.ts, 3, 1))
+
+j.a;
+>j.a : Symbol(a, Decl(mappedTypes7.ts, 0, 13))
+>j : Symbol(j, Decl(mappedTypes7.ts, 10, 13))
+>a : Symbol(a, Decl(mappedTypes7.ts, 0, 13))
+
+j.b;
+>j.b : Symbol(b, Decl(mappedTypes7.ts, 1, 14))
+>j : Symbol(j, Decl(mappedTypes7.ts, 10, 13))
+>b : Symbol(b, Decl(mappedTypes7.ts, 1, 14))
+
+declare const l: L
+>l : Symbol(l, Decl(mappedTypes7.ts, 14, 13))
+>L : Symbol(L, Decl(mappedTypes7.ts, 6, 2))
+
+l.a
+>l.a : Symbol(a, Decl(mappedTypes7.ts, 0, 13))
+>l : Symbol(l, Decl(mappedTypes7.ts, 14, 13))
+>a : Symbol(a, Decl(mappedTypes7.ts, 0, 13))
+

tests/baselines/reference/mappedTypes7.types

@@ -0,0 +1,38 @@
+=== tests/cases/conformance/types/mapped/mappedTypes7.ts ===
+interface I {
+    a: number;
+>a : number
+
+    b: number;
+>b : number
+}
+type J = {
+>J : J
+
+    [K in 'b' | 'a']: I[K]
+};
+
+type L = Pick<J, 'a'>
+>L : Pick<J, "a">
+
+declare const j: J;
+>j : J
+
+j.a;
+>j.a : number
+>j : J
+>a : number
+
+j.b;
+>j.b : number
+>j : J
+>b : number
+
+declare const l: L
+>l : Pick<J, "a">
+
+l.a
+>l.a : number
+>l : Pick<J, "a">
+>a : number
+

tests/cases/conformance/types/mapped/mappedTypes7.ts

@@ -0,0 +1,16 @@
+interface I {
+    a: number;
+    b: number;
+}
+type J = {
+    [K in 'b' | 'a']: I[K]
+};
+
+type L = Pick<J, 'a'>
+
+declare const j: J;
+j.a;
+j.b;
+
+declare const l: L
+l.a