From 759537c5b22ed7f50dc633cd4012511d84a116a3 Mon Sep 17 00:00:00 2001
From: Jack Bates <jack@nottheoilrig.com>
Date: Tue, 15 Oct 2019 13:29:19 -0700
Subject: [PATCH] Don't inferFromIndexTypes() twice

---
 src/compiler/checker.ts                       | 52 +++++++++----------
 .../reference/restTupleElements1.types        |  2 +-
 2 files changed, 27 insertions(+), 27 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 85c6b695063d7..b99bf712ad7d2 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -17921,6 +17921,32 @@ namespace ts {
                 }
                 // Infer from the members of source and target only if the two types are possibly related
                 if (!typesDefinitelyUnrelated(source, target)) {
+                    if (isArrayType(source) || isTupleType(source)) {
+                        if (isTupleType(target)) {
+                            const sourceLength = isTupleType(source) ? getLengthOfTupleType(source) : 0;
+                            const targetLength = getLengthOfTupleType(target);
+                            const sourceRestType = isTupleType(source) ? getRestTypeOfTupleType(source) : getElementTypeOfArrayType(source);
+                            const targetRestType = getRestTypeOfTupleType(target);
+                            const fixedLength = targetLength < sourceLength || sourceRestType ? targetLength : sourceLength;
+                            for (let i = 0; i < fixedLength; i++) {
+                                inferFromTypes(i < sourceLength ? getTypeArguments(<TypeReference>source)[i] : sourceRestType!, getTypeArguments(target)[i]);
+                            }
+                            if (targetRestType) {
+                                const types = fixedLength < sourceLength ? getTypeArguments(<TypeReference>source).slice(fixedLength, sourceLength) : [];
+                                if (sourceRestType) {
+                                    types.push(sourceRestType);
+                                }
+                                if (types.length) {
+                                    inferFromTypes(getUnionType(types), targetRestType);
+                                }
+                            }
+                            return;
+                        }
+                        if (isArrayType(target)) {
+                            inferFromIndexTypes(source, target);
+                            return;
+                        }
+                    }
                     inferFromProperties(source, target);
                     inferFromSignatures(source, target, SignatureKind.Call);
                     inferFromSignatures(source, target, SignatureKind.Construct);
@@ -17929,32 +17955,6 @@ namespace ts {
             }
 
             function inferFromProperties(source: Type, target: Type) {
-                if (isArrayType(source) || isTupleType(source)) {
-                    if (isTupleType(target)) {
-                        const sourceLength = isTupleType(source) ? getLengthOfTupleType(source) : 0;
-                        const targetLength = getLengthOfTupleType(target);
-                        const sourceRestType = isTupleType(source) ? getRestTypeOfTupleType(source) : getElementTypeOfArrayType(source);
-                        const targetRestType = getRestTypeOfTupleType(target);
-                        const fixedLength = targetLength < sourceLength || sourceRestType ? targetLength : sourceLength;
-                        for (let i = 0; i < fixedLength; i++) {
-                            inferFromTypes(i < sourceLength ? getTypeArguments(<TypeReference>source)[i] : sourceRestType!, getTypeArguments(target)[i]);
-                        }
-                        if (targetRestType) {
-                            const types = fixedLength < sourceLength ? getTypeArguments(<TypeReference>source).slice(fixedLength, sourceLength) : [];
-                            if (sourceRestType) {
-                                types.push(sourceRestType);
-                            }
-                            if (types.length) {
-                                inferFromTypes(getUnionType(types), targetRestType);
-                            }
-                        }
-                        return;
-                    }
-                    if (isArrayType(target)) {
-                        inferFromIndexTypes(source, target);
-                        return;
-                    }
-                }
                 const properties = getPropertiesOfObjectType(target);
                 for (const targetProp of properties) {
                     const sourceProp = getPropertyOfType(source, targetProp.escapedName);
diff --git a/tests/baselines/reference/restTupleElements1.types b/tests/baselines/reference/restTupleElements1.types
index 88c98395f21c3..3eb0b00087072 100644
--- a/tests/baselines/reference/restTupleElements1.types
+++ b/tests/baselines/reference/restTupleElements1.types
@@ -173,7 +173,7 @@ f0([]);  // Error
 >[] : never[]
 
 f0([1]);
->f0([1]) : [number, number]
+>f0([1]) : [number, unknown]
 >f0 : <T, U>(x: [T, ...U[]]) => [T, U]
 >[1] : [number]
 >1 : 1