From d136a8e528547d4791a643429276f8f04342d4c7 Mon Sep 17 00:00:00 2001
From: Greg Titus <toon@omnigroup.com>
Date: Fri, 2 Aug 2024 15:58:35 -0700
Subject: [PATCH] Avoid getCalleeLocator() with inner call that is still
 variable type.

---
 lib/Sema/CSSimplify.cpp                  | 15 +++++++++------
 test/Sema/diag_ambiguous_overloads.swift |  9 +++++++++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/lib/Sema/CSSimplify.cpp b/lib/Sema/CSSimplify.cpp
index 318bf82a9d5bd..3bfea7268ecbd 100644
--- a/lib/Sema/CSSimplify.cpp
+++ b/lib/Sema/CSSimplify.cpp
@@ -2080,13 +2080,16 @@ ConstraintSystem::matchFunctionResultTypes(Type expectedResult, Type fnResult,
     auto anchor = locator.getAnchor();
     if (auto *callExpr = getAsExpr<CallExpr>(anchor)) {
       if (auto *innerCall = getAsExpr<CallExpr>(callExpr->getSemanticFn())) {
-        auto *innerCalleeLoc =
+        if (!simplifyType(getType(innerCall->getFn()))
+                 ->is<TypeVariableType>()) {
+          auto *innerCalleeLoc =
             getCalleeLocator(getConstraintLocator(innerCall));
-        if (auto innerOverload = findSelectedOverloadFor(innerCalleeLoc)) {
-          auto choice = innerOverload->choice;
-          if (choice.getFunctionRefKind() == FunctionRefKind::DoubleApply) {
-            isSecondApply = true;
-            selected.emplace(*innerOverload);
+          if (auto innerOverload = findSelectedOverloadFor(innerCalleeLoc)) {
+            auto choice = innerOverload->choice;
+            if (choice.getFunctionRefKind() == FunctionRefKind::DoubleApply) {
+              isSecondApply = true;
+              selected.emplace(*innerOverload);
+            }
           }
         }
       }
diff --git a/test/Sema/diag_ambiguous_overloads.swift b/test/Sema/diag_ambiguous_overloads.swift
index bf8f13cb8e784..5ad8973d938cb 100644
--- a/test/Sema/diag_ambiguous_overloads.swift
+++ b/test/Sema/diag_ambiguous_overloads.swift
@@ -189,3 +189,12 @@ do {
   let _ = i16 -- i16
   // expected-error@-1 {{ambiguous use of operator '--'}}
 }
+
+struct Issue75623 {
+  func f(p: String) {}
+  func f(_: Int) -> (Int) -> Void {}
+
+  func g() {
+    f(0)(0) // was hitting assertion
+  }
+}