Sema: Improve MemberImportVisibility diags for for-in loops.

Ensure that source locations are attached to the implicit calls to
`makeIterator()` and `next()` for diagnostics.

Partially resolves rdar://144535697.

Author: tshortli

lib/Sema/CSGen.cpp

@@ -4602,8 +4602,9 @@ generateForEachStmtConstraints(ConstraintSystem &cs, DeclContext *dc,
     FuncDecl *makeIterator = isAsync ? ctx.getAsyncSequenceMakeAsyncIterator()
                                      : ctx.getSequenceMakeIterator();
 
-    auto *makeIteratorRef = UnresolvedDotExpr::createImplicit(
-        ctx, sequenceExpr, makeIterator->getName());
+    auto *makeIteratorRef = new (ctx) UnresolvedDotExpr(
+        sequenceExpr, SourceLoc(), DeclNameRef(makeIterator->getName()),
+        DeclNameLoc(stmt->getForLoc()), /*implicit=*/true);
     makeIteratorRef->setFunctionRefInfo(FunctionRefInfo::singleBaseNameApply());
 
     Expr *makeIteratorCall =
@@ -4666,11 +4667,13 @@ generateForEachStmtConstraints(ConstraintSystem &cs, DeclContext *dc,
     TinyPtrVector<Identifier> labels;
     if (nextFn && nextFn->getParameters()->size() == 1)
       labels.push_back(ctx.Id_isolation);
-    auto *nextRef = UnresolvedDotExpr::createImplicit(
-        ctx,
+    auto *makeIteratorVarRef =
         new (ctx) DeclRefExpr(makeIteratorVar, DeclNameLoc(stmt->getForLoc()),
-                              /*Implicit=*/true),
-        nextId, labels);
+                              /*Implicit=*/true);
+    auto *nextRef = new (ctx)
+        UnresolvedDotExpr(makeIteratorVarRef, SourceLoc(),
+                          DeclNameRef(DeclName(ctx, nextId, labels)),
+                          DeclNameLoc(stmt->getForLoc()), /*implicit=*/true);
     nextRef->setFunctionRefInfo(FunctionRefInfo::singleBaseNameApply());
 
     ArgumentList *nextArgs;

test/AutoDiff/SILOptimizer/differentiation_control_flow_diagnostics.swift

@@ -168,11 +168,11 @@ enum Tree : Differentiable & AdditiveArithmetic {
 // (`Collection.makeIterator` and `IteratorProtocol.next`).
 // expected-error @+1 {{function is not differentiable}}
 @differentiable(reverse)
-// expected-note @+2 {{when differentiating this function definition}}
-// expected-note @+1 {{cannot differentiate through a non-differentiable result; do you want to use 'withoutDerivative(at:)'?}} {{+2:12-12=withoutDerivative(at: }} {{+2:17-17=)}}
 func loop_array(_ array: [Float]) -> Float {
+  // expected-note@-1 {{when differentiating this function definition}}
   var result: Float = 1
   for x in array {
+    // expected-note@-1 {{cannot differentiate through a non-differentiable result; do you want to use 'withoutDerivative(at:)'}}
     result = result * x
   }
   return result

test/NameLookup/members_transitive_compiler_protocols.swift

@@ -0,0 +1,35 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module -o %t %t/lib.swift
+// RUN: %target-swift-frontend -typecheck -primary-file %t/main.swift %t/other.swift -I %t -verify -enable-upcoming-feature MemberImportVisibility
+
+// REQUIRES: swift_feature_MemberImportVisibility
+
+//--- main.swift
+
+import Swift
+// expected-note 2 {{add import of module 'lib'}}
+
+for _ in makeSequence() { }
+// expected-error@-1 {{instance method 'makeIterator()' is not available due to missing import of defining module 'lib'}}
+// expected-error@-2 {{instance method 'next()' is not available due to missing import of defining module 'lib'}}
+
+//--- other.swift
+
+import lib
+
+func makeSequence() -> EmptySequence {
+  return MySequence()
+}
+
+//--- lib.swift
+
+public struct EmptySequence: Sequence {
+  public struct Iterator: IteratorProtocol {
+    public mutating func next() -> Int? { nil }
+  }
+
+  public func makeIterator() -> Iterator { Iterator() }
+  public init() { }
+}