From 0a628ff0c9c0bd6ef169a28e7052450939b625ec Mon Sep 17 00:00:00 2001
From: Oleksandr T <oleksandr.tarasiuk@outlook.com>
Date: Sat, 6 Nov 2021 00:36:08 +0200
Subject: [PATCH] fix(44059): omit duplicate types (#45739)

---
 src/services/codefixes/inferFromUsage.ts       | 18 +++++++++++++++---
 .../codeFixInferFromUsageVariable4.ts          | 13 +++++++++++++
 2 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 tests/cases/fourslash/codeFixInferFromUsageVariable4.ts

diff --git a/src/services/codefixes/inferFromUsage.ts b/src/services/codefixes/inferFromUsage.ts
index b6b3aea3f02..e680d4307ec 100644
--- a/src/services/codefixes/inferFromUsage.ts
+++ b/src/services/codefixes/inferFromUsage.ts
@@ -1000,13 +1000,25 @@ namespace ts.codefix {
             if (usage.numberIndex) {
                 types.push(checker.createArrayType(combineFromUsage(usage.numberIndex)));
             }
-            if (usage.properties?.size || usage.calls?.length || usage.constructs?.length || usage.stringIndex) {
+            if (usage.properties?.size || usage.constructs?.length || usage.stringIndex) {
                 types.push(inferStructuralType(usage));
             }
 
-            types.push(...(usage.candidateTypes || []).map(t => checker.getBaseTypeOfLiteralType(t)));
-            types.push(...inferNamedTypesFromProperties(usage));
+            const candidateTypes = (usage.candidateTypes || []).map(t => checker.getBaseTypeOfLiteralType(t));
+            const callsType = usage.calls?.length ? inferStructuralType(usage) : undefined;
+            if (callsType && candidateTypes) {
+                types.push(checker.getUnionType([callsType, ...candidateTypes], UnionReduction.Subtype));
+            }
+            else {
+                if (callsType) {
+                    types.push(callsType);
+                }
+                if (length(candidateTypes)) {
+                    types.push(...candidateTypes);
+                }
+            }
 
+            types.push(...inferNamedTypesFromProperties(usage));
             return types;
         }
 
diff --git a/tests/cases/fourslash/codeFixInferFromUsageVariable4.ts b/tests/cases/fourslash/codeFixInferFromUsageVariable4.ts
new file mode 100644
index 00000000000..12db84cfef0
--- /dev/null
+++ b/tests/cases/fourslash/codeFixInferFromUsageVariable4.ts
@@ -0,0 +1,13 @@
+/// <reference path='fourslash.ts' />
+
+// @noImplicitAny: false
+////[|let foo;|]
+////
+////foo?.();
+////foo = () => {}
+
+verify.codeFix({
+    description: "Infer type of 'foo' from usage",
+    index: 0,
+    newRangeContent: "let foo: () => void;"
+});