[Migrator] Add Swift. prefix to type(of:) expressions in Swift 3

This changed to be resolved by overload resolution in Swift 4, and so
can suddenly be shadowed by similarly named properties and functions
that are visible at the expression's location. When in Swift 3 mode, if
there is a visible declaration named "type", add the `Swift.` prefix to
disambiguate in Swift 4 mode.

rdar://problem/31997321

Author: bitjammer

lib/Migrator/SyntacticMigratorPass.cpp

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "swift/AST/NameLookup.h"
 #include "swift/AST/USRGeneration.h"
 #include "swift/AST/ASTVisitor.h"
 #include "swift/Frontend/Frontend.h"
@@ -536,6 +537,38 @@ struct SyntacticMigratorPass::Implementation : public SourceEntityWalker {
       return;
   }
 
+  /// If the expression is `type(of:)`, in Swift 3 it's a special 'dynamic type
+  /// expression'. In Swift 4, this is resolved by overload resolution, so
+  /// if there is a func type(of:) or even var type, it can shadow
+  /// Swift.type(of:), which is probably not what people want.
+  ///
+  /// This migration operation adds `Swift.` to disambiguate in Swift 4.
+  void handleTypeOfFunction(const DynamicTypeExpr *DTE) {
+    if (!SF->getASTContext().LangOpts.isSwiftVersion3()) {
+      return;
+    }
+    const auto CSR = Lexer::getCharSourceRangeFromSourceRange(SM,
+      DTE->getSourceRange());
+    if (SM.extractText(CSR).startswith("Swift.")) {
+      return;
+    }
+
+    UnqualifiedLookup Lookup {
+      { SF->getASTContext().getIdentifier("type") },
+      SF->getModuleScopeContext(),
+      /*TypeResolver=*/nullptr,
+      /*IsKnownPrivate=*/false,
+      DTE->getLoc()
+    };
+    if (Lookup.Results.empty()) {
+      // There won't be a name shadowing here in Swift 4, so we don't need to
+      // do anything.
+      return;
+    }
+
+    Editor.insertBefore(DTE->getLoc(), "Swift.");
+  }
+
   bool walkToExprPre(Expr *E) override {
     if (auto *CE = dyn_cast<CallExpr>(E)) {
       handleTupleArgumentMismatches(CE);
@@ -566,6 +599,11 @@ struct SyntacticMigratorPass::Implementation : public SourceEntityWalker {
         break;
       }
     }
+
+    if (const auto *DTE = dyn_cast<DynamicTypeExpr>(E)) {
+      handleTypeOfFunction(DTE);
+    }
+
     return true;
   }
 

test/Migrator/prefix_typeof_expr.swift

@@ -0,0 +1,27 @@
+// rdar://problem/32025974
+// XFAIL: linux
+// RUN: rm -rf %t && mkdir -p %t && %target-swift-frontend -c -update-code -primary-file %s -emit-migrated-file-path %t/prefix_typeof_expr.swift.result -emit-remap-file-path %t/member.swift.remap -o /dev/null
+// RUN: diff -u %S/prefix_typeof_expr.swift.expected %t/prefix_typeof_expr.swift.result
+
+class HasTypeVar {
+  var type: Int {
+    precondition(true, "\(type(of: self)) should never be asked for its type")
+    _ = Swift.type(of: 1) // Don't add another prefix to this one
+    return 1
+  }
+}
+
+class HasTypeMethod {
+  func type<T>(of: T) -> Int {
+    _ = type(of: 1)
+    _ = Swift.type(of: 1) // Don't add another prefix to this one
+    return 1
+  }
+}
+
+func type<T>(of: T) -> Int {
+  return 1
+}
+
+_ = type(of: 1)
+_ = Swift.type(of: 1) // Don't add another prefix to this one

test/Migrator/prefix_typeof_expr.swift.expected

@@ -0,0 +1,27 @@
+// rdar://problem/32025974
+// XFAIL: linux
+// RUN: rm -rf %t && mkdir -p %t && %target-swift-frontend -c -update-code -primary-file %s -emit-migrated-file-path %t/prefix_typeof_expr.swift.result -emit-remap-file-path %t/member.swift.remap -o /dev/null
+// RUN: diff -u %S/prefix_typeof_expr.swift.expected %t/prefix_typeof_expr.swift.result
+
+class HasTypeVar {
+  var type: Int {
+    precondition(true, "\(Swift.type(of: self)) should never be asked for its type")
+    _ = Swift.type(of: 1) // Don't add another prefix to this one
+    return 1
+  }
+}
+
+class HasTypeMethod {
+  func type<T>(of: T) -> Int {
+    _ = Swift.type(of: 1)
+    _ = Swift.type(of: 1) // Don't add another prefix to this one
+    return 1
+  }
+}
+
+func type<T>(of: T) -> Int {
+  return 1
+}
+
+_ = Swift.type(of: 1)
+_ = Swift.type(of: 1) // Don't add another prefix to this one

test/Migrator/tuple-arguments.swift

@@ -1,4 +1,4 @@
-// FIXME: Figure out why this is not working on linux
+// rdar://problem/32025974
 // XFAIL: linux
 
 // RUN: %target-swift-frontend -typecheck %s -swift-version 3

test/Migrator/tuple-arguments.swift.expected

@@ -1,4 +1,4 @@
-// FIXME: Figure out why this is not working on linux
+// rdar://problem/32025974
 // XFAIL: linux
 
 // RUN: %target-swift-frontend -typecheck %s -swift-version 3