From e4babd40e00f572c3f308e47c8d98e2d7df550a4 Mon Sep 17 00:00:00 2001
From: Eli Barzilay <eli@barzilay.org>
Date: Fri, 27 Mar 2020 15:54:34 -0400
Subject: [PATCH] Skip `isBlockScopedNameDeclaredBeforeUse` error in interface
 or type declarations

Fixes #35947.
---
 src/compiler/checker.ts                       |  6 +++-
 .../reference/forwardRefInTypeDeclaration.js  | 18 ++++++++++++
 .../forwardRefInTypeDeclaration.symbols       | 27 +++++++++++++++++
 .../forwardRefInTypeDeclaration.types         | 29 +++++++++++++++++++
 .../compiler/forwardRefInTypeDeclaration.ts   | 11 +++++++
 5 files changed, 90 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/forwardRefInTypeDeclaration.js
 create mode 100644 tests/baselines/reference/forwardRefInTypeDeclaration.symbols
 create mode 100644 tests/baselines/reference/forwardRefInTypeDeclaration.types
 create mode 100644 tests/cases/compiler/forwardRefInTypeDeclaration.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index ac38c26d62e..6ebcbdc2227 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1418,7 +1418,7 @@ namespace ts {
                 return true;
             }
 
-            if (!!(usage.flags & NodeFlags.JSDoc) || isInTypeQuery(usage)) {
+            if (!!(usage.flags & NodeFlags.JSDoc) || isInTypeQuery(usage) || usageInTypeDeclaration()) {
                 return true;
             }
             if (isUsedInFunctionOrInstanceProperty(usage, declaration)) {
@@ -1432,6 +1432,10 @@ namespace ts {
             }
             return false;
 
+            function usageInTypeDeclaration() {
+                return !!findAncestor(usage, node => isInterfaceDeclaration(node) || isTypeAliasDeclaration(node));
+            }
+
             function isImmediatelyUsedInInitializerOfBlockScopedVariable(declaration: VariableDeclaration, usage: Node): boolean {
                 switch (declaration.parent.parent.kind) {
                     case SyntaxKind.VariableStatement:
diff --git a/tests/baselines/reference/forwardRefInTypeDeclaration.js b/tests/baselines/reference/forwardRefInTypeDeclaration.js
new file mode 100644
index 00000000000..ee2dda355f6
--- /dev/null
+++ b/tests/baselines/reference/forwardRefInTypeDeclaration.js
@@ -0,0 +1,18 @@
+//// [forwardRefInTypeDeclaration.ts]
+// forward ref ignored in a typeof
+declare let s: typeof s1;
+const s1 = "x";
+
+// ignored anywhere in an interface (#35947)
+interface Foo2 { [s2]: number; }
+const s2 = "x";
+
+// or in a type definition
+type Foo3 = { [s3]: number; }
+const s3 = "x";
+
+
+//// [forwardRefInTypeDeclaration.js]
+var s1 = "x";
+var s2 = "x";
+var s3 = "x";
diff --git a/tests/baselines/reference/forwardRefInTypeDeclaration.symbols b/tests/baselines/reference/forwardRefInTypeDeclaration.symbols
new file mode 100644
index 00000000000..f8ad803779c
--- /dev/null
+++ b/tests/baselines/reference/forwardRefInTypeDeclaration.symbols
@@ -0,0 +1,27 @@
+=== tests/cases/compiler/forwardRefInTypeDeclaration.ts ===
+// forward ref ignored in a typeof
+declare let s: typeof s1;
+>s : Symbol(s, Decl(forwardRefInTypeDeclaration.ts, 1, 11))
+>s1 : Symbol(s1, Decl(forwardRefInTypeDeclaration.ts, 2, 5))
+
+const s1 = "x";
+>s1 : Symbol(s1, Decl(forwardRefInTypeDeclaration.ts, 2, 5))
+
+// ignored anywhere in an interface (#35947)
+interface Foo2 { [s2]: number; }
+>Foo2 : Symbol(Foo2, Decl(forwardRefInTypeDeclaration.ts, 2, 15))
+>[s2] : Symbol(Foo2[s2], Decl(forwardRefInTypeDeclaration.ts, 5, 16))
+>s2 : Symbol(s2, Decl(forwardRefInTypeDeclaration.ts, 6, 5))
+
+const s2 = "x";
+>s2 : Symbol(s2, Decl(forwardRefInTypeDeclaration.ts, 6, 5))
+
+// or in a type definition
+type Foo3 = { [s3]: number; }
+>Foo3 : Symbol(Foo3, Decl(forwardRefInTypeDeclaration.ts, 6, 15))
+>[s3] : Symbol([s3], Decl(forwardRefInTypeDeclaration.ts, 9, 13))
+>s3 : Symbol(s3, Decl(forwardRefInTypeDeclaration.ts, 10, 5))
+
+const s3 = "x";
+>s3 : Symbol(s3, Decl(forwardRefInTypeDeclaration.ts, 10, 5))
+
diff --git a/tests/baselines/reference/forwardRefInTypeDeclaration.types b/tests/baselines/reference/forwardRefInTypeDeclaration.types
new file mode 100644
index 00000000000..de487ec372c
--- /dev/null
+++ b/tests/baselines/reference/forwardRefInTypeDeclaration.types
@@ -0,0 +1,29 @@
+=== tests/cases/compiler/forwardRefInTypeDeclaration.ts ===
+// forward ref ignored in a typeof
+declare let s: typeof s1;
+>s : "x"
+>s1 : "x"
+
+const s1 = "x";
+>s1 : "x"
+>"x" : "x"
+
+// ignored anywhere in an interface (#35947)
+interface Foo2 { [s2]: number; }
+>[s2] : number
+>s2 : "x"
+
+const s2 = "x";
+>s2 : "x"
+>"x" : "x"
+
+// or in a type definition
+type Foo3 = { [s3]: number; }
+>Foo3 : Foo3
+>[s3] : number
+>s3 : "x"
+
+const s3 = "x";
+>s3 : "x"
+>"x" : "x"
+
diff --git a/tests/cases/compiler/forwardRefInTypeDeclaration.ts b/tests/cases/compiler/forwardRefInTypeDeclaration.ts
new file mode 100644
index 00000000000..ef29f727862
--- /dev/null
+++ b/tests/cases/compiler/forwardRefInTypeDeclaration.ts
@@ -0,0 +1,11 @@
+// forward ref ignored in a typeof
+declare let s: typeof s1;
+const s1 = "x";
+
+// ignored anywhere in an interface (#35947)
+interface Foo2 { [s2]: number; }
+const s2 = "x";
+
+// or in a type definition
+type Foo3 = { [s3]: number; }
+const s3 = "x";