From 6ccd01393bacd83cf5d2ffaff6b4df177dd45372 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Tue, 4 Aug 2020 14:00:59 -0700
Subject: [PATCH] [Diagnostics] Detect and diagnose type mismatches related to
 function builder result

Generic requirement failures are already covered but general type
mismatches have to be handled separately.

Resolves: rdar://problem/65413640
(cherry picked from commit 98007904b83a6cc5ef3b8320635c9258972dfcff)
---
 lib/Sema/CSDiagnostics.cpp                    | 5 +++++
 lib/Sema/CSSimplify.cpp                       | 6 ++++++
 lib/Sema/ConstraintSystem.cpp                 | 5 +++++
 test/Constraints/function_builder_diags.swift | 4 ++++
 4 files changed, 20 insertions(+)

diff --git a/lib/Sema/CSDiagnostics.cpp b/lib/Sema/CSDiagnostics.cpp
index 257c7fb22c3d1..e1a7f1089b99d 100644
--- a/lib/Sema/CSDiagnostics.cpp
+++ b/lib/Sema/CSDiagnostics.cpp
@@ -2107,6 +2107,11 @@ bool ContextualFailure::diagnoseAsError() {
     return true;
   }
 
+  case ConstraintLocator::FunctionBuilderBodyResult: {
+    diagnostic = *getDiagnosticFor(CTP_Initialization, toType);
+    break;
+  }
+
   default:
     return false;
   }
diff --git a/lib/Sema/CSSimplify.cpp b/lib/Sema/CSSimplify.cpp
index da385f2b0d5c0..74acf2bffa059 100644
--- a/lib/Sema/CSSimplify.cpp
+++ b/lib/Sema/CSSimplify.cpp
@@ -4264,6 +4264,12 @@ bool ConstraintSystem::repairFailures(
     break;
   }
 
+  case ConstraintLocator::FunctionBuilderBodyResult: {
+    conversionsOrFixes.push_back(ContextualMismatch::create(
+        *this, lhs, rhs, getConstraintLocator(locator)));
+    break;
+  }
+
   default:
     break;
   }
diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 740382e1d352f..a1e7e6e48d984 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -3531,6 +3531,11 @@ void constraints::simplifyLocator(Expr *&anchor,
       continue;
     }
 
+    case ConstraintLocator::FunctionBuilderBodyResult: {
+      path = path.slice(1);
+      break;
+    }
+
     default:
       // FIXME: Lots of other cases to handle.
       break;
diff --git a/test/Constraints/function_builder_diags.swift b/test/Constraints/function_builder_diags.swift
index 66a9ecaca9df0..0e32913c39619 100644
--- a/test/Constraints/function_builder_diags.swift
+++ b/test/Constraints/function_builder_diags.swift
@@ -602,4 +602,8 @@ struct MyView {
     case . // expected-error {{expected ':' after 'case'}}
     } // expected-error {{expected identifier after '.' expression}}
   }
+
+  @TupleBuilder var invalidConversion: Int {
+    "" // expected-error {{cannot convert value of type 'String' to specified type 'Int'}}
+  }
 }