Fixed a redundant used before defined error

src/compiler/checker.ts

@@ -2773,6 +2773,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return sourceFiles.indexOf(declarationFile) <= sourceFiles.indexOf(useFile);
         }
 
+        // deferred usage in a type context is always OK regardless of the usage position:
+        if (!!(usage.flags & NodeFlags.JSDoc) || isInTypeQuery(usage) || isInAmbientOrTypeNode(usage)) {
+            return true;
+        }
+
         if (declaration.pos <= usage.pos && !(isPropertyDeclaration(declaration) && isThisProperty(usage.parent) && !declaration.initializer && !declaration.exclamationToken)) {
             // declaration is before usage
             if (declaration.kind === SyntaxKind.BindingElement) {
@@ -2813,9 +2818,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         //    (except when emitStandardClassFields: true and the reference is to a parameter property)
         // 4. inside a static property initializer, a reference to a static method in the same class
         // 5. inside a TS export= declaration (since we will move the export statement during emit to avoid TDZ)
-        // or if usage is in a type context:
-        // 1. inside a type query (typeof in type position)
-        // 2. inside a jsdoc comment
         if (usage.parent.kind === SyntaxKind.ExportSpecifier || (usage.parent.kind === SyntaxKind.ExportAssignment && (usage.parent as ExportAssignment).isExportEquals)) {
             // export specifiers do not use the variable, they only make it available for use
             return true;
@@ -2825,9 +2827,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return true;
         }
 
-        if (!!(usage.flags & NodeFlags.JSDoc) || isInTypeQuery(usage) || isInAmbientOrTypeNode(usage)) {
-            return true;
-        }
         if (isUsedInFunctionOrInstanceProperty(usage, declaration)) {
             if (
                 emitStandardClassFields

tests/baselines/reference/noUsedBeforeDefinedErrorInTypeContext.symbols

@@ -0,0 +1,50 @@
+//// [tests/cases/compiler/noUsedBeforeDefinedErrorInTypeContext.ts] ////
+
+=== noUsedBeforeDefinedErrorInTypeContext.ts ===
+// https://github.com/microsoft/TypeScript/issues/8775
+
+interface IThing<T> {
+>IThing : Symbol(IThing, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 0, 0))
+>T : Symbol(T, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 2, 17))
+
+    owner: T;
+>owner : Symbol(IThing.owner, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 2, 21))
+>T : Symbol(T, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 2, 17))
+}
+
+var foo = {
+>foo : Symbol(foo, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 6, 3))
+
+    one: {} as IThing<typeof foo>,
+>one : Symbol(one, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 6, 11))
+>IThing : Symbol(IThing, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 0, 0))
+>foo : Symbol(foo, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 6, 3))
+}
+
+let baz = {
+>baz : Symbol(baz, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 10, 3))
+
+    two: {} as IThing<typeof bar>,
+>two : Symbol(two, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 10, 11))
+>IThing : Symbol(IThing, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 0, 0))
+>bar : Symbol(bar, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 14, 3))
+}
+
+let bar = {
+>bar : Symbol(bar, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 14, 3))
+
+    three: {} as IThing<typeof bar>,
+>three : Symbol(three, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 14, 11))
+>IThing : Symbol(IThing, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 0, 0))
+>bar : Symbol(bar, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 14, 3))
+}
+
+const qwe = {
+>qwe : Symbol(qwe, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 18, 5))
+
+    four: {} as IThing<typeof qwe>,
+>four : Symbol(four, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 18, 13))
+>IThing : Symbol(IThing, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 0, 0))
+>qwe : Symbol(qwe, Decl(noUsedBeforeDefinedErrorInTypeContext.ts, 18, 5))
+}
+

tests/baselines/reference/noUsedBeforeDefinedErrorInTypeContext.types

@@ -0,0 +1,54 @@
+//// [tests/cases/compiler/noUsedBeforeDefinedErrorInTypeContext.ts] ////
+
+=== noUsedBeforeDefinedErrorInTypeContext.ts ===
+// https://github.com/microsoft/TypeScript/issues/8775
+
+interface IThing<T> {
+    owner: T;
+>owner : T
+}
+
+var foo = {
+>foo : any
+>{    one: {} as IThing<typeof foo>,} : { one: IThing<any>; }
+
+    one: {} as IThing<typeof foo>,
+>one : IThing<any>
+>{} as IThing<typeof foo> : IThing<any>
+>{} : {}
+>foo : any
+}
+
+let baz = {
+>baz : { two: IThing<any>; }
+>{    two: {} as IThing<typeof bar>,} : { two: IThing<any>; }
+
+    two: {} as IThing<typeof bar>,
+>two : IThing<any>
+>{} as IThing<typeof bar> : IThing<any>
+>{} : {}
+>bar : any
+}
+
+let bar = {
+>bar : any
+>{    three: {} as IThing<typeof bar>,} : { three: IThing<any>; }
+
+    three: {} as IThing<typeof bar>,
+>three : IThing<any>
+>{} as IThing<typeof bar> : IThing<any>
+>{} : {}
+>bar : any
+}
+
+const qwe = {
+>qwe : any
+>{    four: {} as IThing<typeof qwe>,} : { four: IThing<any>; }
+
+    four: {} as IThing<typeof qwe>,
+>four : IThing<any>
+>{} as IThing<typeof qwe> : IThing<any>
+>{} : {}
+>qwe : any
+}
+

tests/cases/compiler/noUsedBeforeDefinedErrorInTypeContext.ts

@@ -0,0 +1,23 @@
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/8775
+
+interface IThing<T> {
+    owner: T;
+}
+
+var foo = {
+    one: {} as IThing<typeof foo>,
+}
+
+let baz = {
+    two: {} as IThing<typeof bar>,
+}
+
+let bar = {
+    three: {} as IThing<typeof bar>,
+}
+
+const qwe = {
+    four: {} as IThing<typeof qwe>,
+}