ASTScope: PatternEntryDeclScope changes the insertion point for local bindings

This gives us the desired behavior, where local bindings are in
scope after their definition.

Note that BraceStmt still introduces all bindings at the beginning,
but now we change BraceStmt to only introduce local functions and
types, allowing us to disable parse-time lookup.

Author: slavapestov

lib/AST/ASTScopeCreation.cpp

@@ -38,11 +38,6 @@
 using namespace swift;
 using namespace ast_scope;
 
-/// If true, nest scopes so a variable is out of scope before its declaration
-/// Does not handle capture rules for local functions properly.
-/// If false don't push uses down into subscopes after decls.
-static const bool handleUseBeforeDef = false;
-
 #pragma mark source range utilities
 static bool rangeableIsIgnored(const Decl *d) { return d->isImplicit(); }
 static bool rangeableIsIgnored(const Expr *d) {
@@ -746,11 +741,11 @@ class NodeAdder
     if (auto *var = patternBinding->getSingleVar())
       scopeCreator.addChildrenForKnownAttributes(var, parentScope);
 
-    const bool isInTypeDecl = parentScope->isATypeDeclScope();
+    const bool isLocalBinding = patternBinding->getDeclContext()->isLocalContext();
 
     const DeclVisibilityKind vis =
-        isInTypeDecl ? DeclVisibilityKind::MemberOfCurrentNominal
-                     : DeclVisibilityKind::LocalVariable;
+        isLocalBinding ? DeclVisibilityKind::LocalVariable
+                       : DeclVisibilityKind::MemberOfCurrentNominal;
     auto *insertionPoint = parentScope;
     for (auto i : range(patternBinding->getNumPatternEntries())) {
       insertionPoint =
@@ -759,9 +754,12 @@ class NodeAdder
                   insertionPoint, patternBinding, i, vis)
               .getPtrOr(insertionPoint);
     }
-    // If in a type decl, the type search will find these,
-    // but if in a brace stmt, must continue under the last binding.
-    return isInTypeDecl ? parentScope : insertionPoint;
+
+    ASTScopeAssert(isLocalBinding || insertionPoint == parentScope,
+                   "Bindings at the top-level or members of types should "
+                   "not change the insertion point");
+
+    return insertionPoint;
   }
 
   NullablePtr<ASTScopeImpl> visitEnumElementDecl(EnumElementDecl *eed,
@@ -1041,11 +1039,13 @@ PatternEntryDeclScope::expandAScopeThatCreatesANewInsertionPoint(
     scopeCreator.addChildrenForAllLocalizableAccessorsInSourceOrder(var, this);
   });
 
-  ASTScopeAssert(!handleUseBeforeDef,
-                 "next line is wrong otherwise; would need a use scope");
+  // In local context, the PatternEntryDeclScope becomes the insertion point, so
+  // that all any bindings introduecd by the pattern are in scope for subsequent
+  // lookups.
+  if (vis == DeclVisibilityKind::LocalVariable)
+    return {this, "All code that follows is inside this scope"};
 
-  return {getParent().get(), "When not handling use-before-def, succeeding "
-                             "code just goes in the same scope as this one"};
+  return {getParent().get(), "Global and type members do not introduce scopes"};
 }
 
 void

test/NameLookup/scope_map_top_level.swift

@@ -31,8 +31,8 @@ var i: Int = b.my_identity()
 // CHECK-EXPANDED-NEXT:   `-NominalTypeBodyScope {{.*}}, [4:11 - 4:13]
 // CHECK-EXPANDED-NEXT: `-TopLevelCodeScope {{.*}}, [6:1 - 21:28]
 // CHECK-EXPANDED-NEXT:   `-BraceStmtScope {{.*}}, [6:1 - 21:28]
-// CHECK-EXPANDED-NEXT:     |-PatternEntryDeclScope {{.*}}, [6:5 - 6:15] entry 0 'a'
-// CHECK-EXPANDED-NEXT:       `-PatternEntryInitializerScope {{.*}}, [6:15 - 6:15] entry 0 'a'
+// CHECK-EXPANDED-NEXT:     `-PatternEntryDeclScope {{.*}}, [6:5 - 21:28] entry 0 'a'
+// CHECK-EXPANDED-NEXT:       |-PatternEntryInitializerScope {{.*}}, [6:15 - 6:15] entry 0 'a'
 // CHECK-EXPANDED-NEXT:     `-TopLevelCodeScope {{.*}}, [8:1 - 21:28]
 // CHECK-EXPANDED-NEXT:       `-BraceStmtScope {{.*}}, [8:1 - 21:28]
 // CHECK-EXPANDED-NEXT:         `-GuardStmtScope {{.*}}, [8:1 - 21:28]
@@ -46,9 +46,9 @@ var i: Int = b.my_identity()
 // CHECK-EXPANDED-NEXT:                 `-BraceStmtScope {{.*}}, [11:18 - 11:19]
 // CHECK-EXPANDED-NEXT:             `-TopLevelCodeScope {{.*}}, [13:1 - 21:28]
 // CHECK-EXPANDED-NEXT:               `-BraceStmtScope {{.*}}, [13:1 - 21:28]
-// CHECK-EXPANDED-NEXT:                 |-PatternEntryDeclScope {{.*}}, [13:5 - 13:9] entry 0 'c'
-// CHECK-EXPANDED-NEXT:                   `-PatternEntryInitializerScope {{.*}}, [13:9 - 13:9] entry 0 'c'
-// CHECK-EXPANDED-NEXT:                 |-TypeAliasDeclScope {{.*}}, [15:1 - 15:15]
+// CHECK-EXPANDED-NEXT:                 `-PatternEntryDeclScope {{.*}}, [13:5 - 21:28] entry 0 'c'
+// CHECK-EXPANDED-NEXT:                   |-PatternEntryInitializerScope {{.*}}, [13:9 - 13:9] entry 0 'c'
+// CHECK-EXPANDED-NEXT:                   |-TypeAliasDeclScope {{.*}}, [15:1 - 15:15]
 // CHECK-EXPANDED-NEXT:                 |-ExtensionDeclScope {{.*}}, [17:14 - 19:1]
 // CHECK-EXPANDED-NEXT:                   `-ExtensionBodyScope {{.*}}, [17:15 - 19:1]
 // CHECK-EXPANDED-NEXT:                     `-AbstractFunctionDeclScope {{.*}}, [18:3 - 18:43] 'my_identity()'