Don't add variables declared in 'guard let' to a SourceFile's Decls.

These variables really are local variables -- they have have a
TopLevelCodeDecl as their DeclContext rather than the SourceFile.
Treating them as global variables caused crashes in serialization.

We need an overhaul of top-level variables in script files anyway
(see rdar://problem/20992489&21628526), but this fixes the immediate
issue.

rdar://problem/21928533

Swift SVN r30519

Author: jrose-apple

lib/AST/NameLookup.cpp

@@ -344,7 +344,7 @@ struct FindLocalVal : public StmtVisitor<FindLocalVal> {
   void checkSourceFile(const SourceFile &SF) {
     for (Decl *D : SF.Decls) {
       if (TopLevelCodeDecl *TLCD = dyn_cast<TopLevelCodeDecl>(D))
-        visit(TLCD->getBody());
+        visitBraceStmt(TLCD->getBody(), /*isTopLevel=*/true);
     }
   }
 
@@ -364,6 +364,17 @@ struct FindLocalVal : public StmtVisitor<FindLocalVal> {
       visit(S->getElseStmt());
   }
   void visitGuardStmt(GuardStmt *S) {
+    if (SM.isBeforeInBuffer(Loc, S->getStartLoc()))
+      return;
+
+    // Names in the guard aren't visible until after the pattern.
+    if (!IntersectsRange(S->getBody()->getSourceRange())) {
+      for (const StmtConditionElement &condition : S->getCond()) {
+        if (auto *pattern = condition.getPatternOrNull())
+          checkPattern(pattern, DeclVisibilityKind::LocalVariable);
+      }
+    }
+
     visit(S->getBody());
   }
   void visitIfConfigStmt(IfConfigStmt *S) {
@@ -413,9 +424,15 @@ struct FindLocalVal : public StmtVisitor<FindLocalVal> {
     visit(S->getBody());
     checkPattern(S->getPattern(), DeclVisibilityKind::LocalVariable);
   }
-  void visitBraceStmt(BraceStmt *S) {
-    if (!IntersectsRange(S->getSourceRange()))
-      return;
+  void visitBraceStmt(BraceStmt *S, bool isTopLevelCode = false) {
+    if (isTopLevelCode) {
+      if (SM.isBeforeInBuffer(Loc, S->getStartLoc()))
+        return;
+    } else {
+      if (!IntersectsRange(S->getSourceRange()))
+        return;
+    }
+
     for (auto elem : S->getElements()) {
       if (Stmt *S = elem.dyn_cast<Stmt*>())
         visit(S);

lib/Parse/ParseStmt.cpp

@@ -370,13 +370,16 @@ ParserStatus Parser::parseBraceItems(SmallVectorImpl<ASTNode> &Entries,
 
         // If the parsed stmt was a GuardStmt, push the VarDecls into the
         // Entries list, so that they can be found by unqual name lookup later.
-        if (auto guard = dyn_cast_or_null<GuardStmt>(Result.dyn_cast<Stmt*>())){
-          for (const auto &elt : guard->getCond()) {
-            if (!elt.getPatternOrNull()) continue;
-
-            elt.getPattern()->forEachVariable([&](VarDecl *VD) {
-              Entries.push_back(VD);
-            });
+        if (!IsTopLevel) {
+          auto resultStmt = Result.dyn_cast<Stmt*>();
+          if (auto guard = dyn_cast_or_null<GuardStmt>(resultStmt)) {
+            for (const auto &elt : guard->getCond()) {
+              if (!elt.getPatternOrNull()) continue;
+
+              elt.getPattern()->forEachVariable([&](VarDecl *VD) {
+                Entries.push_back(VD);
+              });
+            }
           }
         }
       }

test/Parse/guard-top-level.swift

@@ -0,0 +1,9 @@
+// RUN: %target-parse-verify-swift
+
+let a: Int? = 1
+guard let b = a else {
+}
+
+func foo() {} // to interrupt the TopLevelCodeDecl
+
+let c = b

test/Serialization/Inputs/top-level-code-other.swift

@@ -0,0 +1,5 @@
+func use(x: Int) {}
+func test() {
+  use(a!)
+  use(b) // expected-error {{use of unresolved identifier 'b'}}
+}

test/Serialization/top-level-code.swift

@@ -0,0 +1,13 @@
+// RUN: rm -rf %t && mkdir %t
+// RUN: %target-swift-frontend -emit-module -o %t %s -module-name Test
+// RUN: llvm-bcanalyzer %t/Test.swiftmodule | FileCheck %s
+
+// RUN: cp %s %t/main.swift
+// RUN: %target-swift-frontend -parse -verify %t/main.swift -primary-file %S/Inputs/top-level-code-other.swift
+
+// CHECK-NOT: UnknownCode
+
+let a: Int? = 1
+guard let b = a else {
+  fatalError()
+}