Ensure that we assign discriminators for closures from top-level macros

In top-level code, we were incorrectly pulling closure discriminators
from TopLevelCodeDecls, not from the enclosing source file, which could
lead to the same discriminators being assigned to different closures that
come from macro expansions at the top level. Hilarity ensures, yet I am
not amused.

Adjust the DeclContext appropriately when computing discriminators.

Fixes rdar://123836908.

Author: DougGregor

lib/AST/ASTContext.cpp

@@ -2193,12 +2193,20 @@ unsigned ASTContext::getNextMacroDiscriminator(
 
 /// Get the next discriminator within the given declaration context.
 unsigned ASTContext::getNextDiscriminator(const DeclContext *dc) {
+  // Top-level code declarations don't have their own discriminators.
+  if (auto tlcd = dyn_cast<TopLevelCodeDecl>(dc))
+    dc = tlcd->getParent();
+
   return getImpl().NextDiscriminator[dc];
 }
 
 /// Set the maximum assigned discriminator within the given declaration context.
 void ASTContext::setMaxAssignedDiscriminator(
     const DeclContext *dc, unsigned discriminator) {
+  // Top-level code declarations don't have their own discriminators.
+  if (auto tlcd = dyn_cast<TopLevelCodeDecl>(dc))
+    dc = tlcd->getParent();
+
   assert(discriminator >= getImpl().NextDiscriminator[dc]);
   getImpl().NextDiscriminator[dc] = discriminator;
 }

lib/AST/ASTDumper.cpp

@@ -1747,11 +1747,6 @@ void swift::printContext(raw_ostream &os, DeclContext *dc) {
         << "autoclosure discriminator=";
     }
 
-    // If we aren't printing to standard error or the debugger output stream,
-    // this client expects to see the computed discriminator. Compute it now.
-    if (&os != &llvm::errs() && &os != &llvm::dbgs())
-      (void)ACE->getDiscriminator();
-
     PrintWithColorRAII(os, DiscriminatorColor) << ACE->getRawDiscriminator();
     break;
   }
@@ -2782,12 +2777,6 @@ class PrintExpr : public ExprVisitor<PrintExpr, void, StringRef>,
   void printClosure(AbstractClosureExpr *E, char const *name,
                                   StringRef label) {
     printCommon(E, name, label);
-
-    // If we aren't printing to standard error or the debugger output stream,
-    // this client expects to see the computed discriminator. Compute it now.
-    if (hasNonStandardOutput())
-      (void)E->getDiscriminator();
-
     printField(E->getRawDiscriminator(), "discriminator", DiscriminatorColor);
 
     switch (auto isolation = E->getActorIsolation()) {

test/Macros/macro_expand_toplevel.swift

@@ -0,0 +1,15 @@
+// REQUIRES: swift_swift_parser, executable_test
+
+// RUN: %empty-directory(%t)
+// RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift
+
+// RUN: %target-build-swift -swift-version 5 -g -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -Xfrontend -emit-dependencies-path -Xfrontend %t/main.d -Xfrontend -emit-reference-dependencies-path -Xfrontend %t/main.swiftdeps
+// RUN: %target-codesign %t/main
+// RUN: %target-run %t/main | %FileCheck %s
+
+@freestanding(expression) macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroDefinition", type: "StringifyMacro")
+
+// CHECK: 3
+// CHECK-NEXT: 7
+print(#stringify({ 1 + 2 }()))
+print(#stringify({ 3 + 4 }()))