[Tooling] Add a utility function to replace one nested name with another.

[bkramer]

Summary

One problem in clang-tidy and other clang tools face is that there is no
way to lookup an arbitrary name in the AST, that's buried deep inside Sema
and might not even be what the user wants as the new name may be freshly
inserted and not available in the AST.

A common use case for lookups is replacing one nested name with another
while minimizing namespace qualifications, so replacing 'ns::foo' with
'ns::bar' will use just 'bar' if we happen to be inside the namespace 'ns'.
This adds a little helper utility for exactly that use case.

[klimek]

include/clang/Tooling/Core/Lookup.h

38–39

Don't most tests violate the "should be fully qualified" requirement here?

lib/Tooling/Core/Lookup.cpp

61

s/of/off/

64–67

If NewName is fully qualified, why would we ever want to allow that to match from a non-global namespace?

namespace a { namespace b { namespace c {
void foo();
}}}

-> if NewName is "::c::bar" (for whatever reason), this should probably not silently go to bar inside 'c', or to c::bar inside 'b'.

73

Isn't that more like isFullyQualified then?

unittests/Tooling/LookupTest.cpp

20–21

Is this ever not true?

[bkramer]

• Removed "fully qualified" in favor of just "qualified" to clarify that the name should be qualified but the leading "::" is not necessary.
• Renamed isNameSpecifierGlobal
• Removed always true conditional from test

[bkramer]

Add more comments and polish test cases.

[klimek]

include/clang/Tooling/Core/Lookup.h

37–38

After some pondering, I think we should require a fully qualified name, as then it's really unambiguous from the call site what is happening.

unittests/Tooling/LookupTest.cpp

69–73

Do we already have a test that tests c::bar with replaceCallExpr(Expr, "a::c::bar"), or do you think that obviously works from this test?

[bkramer]

Enforce :: at the beginning of the new name.

[klimek]

lg

include/clang/Tooling/Core/Lookup.h

+//===--- Lookup.h - Framework for clang refactoring tools --*- C++ -*------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines helper methods for clang tools performing name lookup.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLING_CORE_LOOKUP_H
+#define LLVM_CLANG_TOOLING_CORE_LOOKUP_H
+
+#include "clang/Basic/LLVM.h"
+#include <string>
+
+namespace clang {
+
+class DeclContext;
+class NamedDecl;
+class NestedNameSpecifier;
+
+namespace tooling {
+
+/// Emulate a lookup to replace one nested name specifier with another using as
+/// few additional namespace qualifications as possible.
+///
+/// This does not perform a full C++ lookup so ADL will not work.
+///
+/// \param Use The nested name to be replaced.
+/// \param UseContext The context in which the nested name is contained. This
+///                   will be used to minimize namespace qualifications.
+/// \param FromDecl The declaration to which the nested name points.
+/// \param ReplacementString The replacement nested name. Should be qualified,
+///                          leading "::" is optional.
+/// \returns The new name to be inserted in place of the current nested name.
+std::string replaceNestedName(const NestedNameSpecifier *Use,
+                              const DeclContext *UseContext,
+                              const NamedDecl *FromDecl,
+                              StringRef ReplacementString);
+
+} // end namespace tooling
+} // end namespace clang
+
+#endif // LLVM_CLANG_TOOLING_CORE_LOOKUP_H

lib/Tooling/Core/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangToolingCore
+  Lookup.cpp
   Replacement.cpp
 
   LINK_LIBS
   clangBasic
   clangLex
   clangRewrite
   )

lib/Tooling/Core/Lookup.cpp

+//===--- Lookup.cpp - Framework for clang refactoring tools ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines helper methods for clang tools performing name lookup.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Tooling/Core/Lookup.h"
+#include "clang/AST/Decl.h"
+using namespace clang;
+using namespace clang::tooling;
+
+static bool isInsideDifferentNamespaceWithSameName(const DeclContext *DeclA,
+                                                   const DeclContext *DeclB) {
+  while (true) {
+    // Look past non-namespaces on DeclA.
+    while (DeclA && !isa<NamespaceDecl>(DeclA))
+      DeclA = DeclA->getParent();
+
+    // Look past non-namespaces on DeclB.
+    while (DeclB && !isa<NamespaceDecl>(DeclB))
+      DeclB = DeclB->getParent();
+
+    // We hit the root, no namespace collision.
+    if (!DeclA || !DeclB)
+      return false;
+
+    // Literally the same namespace, not a collision.
+    if (DeclA == DeclB)
+      return false;
+
+    // Now check the names. If they match we have a different namespace with the
+    // same name.
+    if (cast<NamespaceDecl>(DeclA)->getDeclName() ==
+        cast<NamespaceDecl>(DeclB)->getDeclName())
+      return true;
+
+    DeclA = DeclA->getParent();
+    DeclB = DeclB->getParent();
+  }
+}
+
+static std::string getBestNamespaceSubstr(const DeclContext *DeclA,
+                                          StringRef NewName,
+                                          bool HadLeadingColonColon) {
+  while (true) {
+    while (DeclA && !isa<NamespaceDecl>(DeclA))
+      DeclA = DeclA->getParent();
+
+    // Fully qualified it is! Leave :: in place if it's there already.
+    if (!DeclA)
+      return HadLeadingColonColon ? "::" + NewName.str() : NewName.str();
+
+    // Otherwise strip off redundant namespace qualifications from the new name.
+    // We use the fully qualified name of the namespace and remove that part
+    // from NewName if it has an identical prefix.
+    std::string NS =
+        cast<NamespaceDecl>(DeclA)->getQualifiedNameAsString() + "::";
+    if (NewName.startswith("::"))
+      NS = "::" + NS;
+    if (NewName.startswith(NS))
+      return NewName.substr(NS.size());
+
+    // No match yet. Strip of a namespace from the end of the chain and try
+    // again. This allows to get optimal qualifications even if the old and new
+    // decl only share common namespaces at a higher level.
+    DeclA = DeclA->getParent();
+  }
+}
+
+/// Check if the name specifier begins with a written "::".
+static bool isFullyQualified(const NestedNameSpecifier *NNS) {
+  while (NNS) {
+    if (NNS->getKind() == NestedNameSpecifier::Global)
+      return true;
+    NNS = NNS->getPrefix();
+  }
+  return false;
+}
+
+std::string tooling::replaceNestedName(const NestedNameSpecifier *Use,
+                                       const DeclContext *UseContext,
+                                       const NamedDecl *FromDecl,
+                                       StringRef ReplacementString) {
+  // We can do a raw name replacement when we are not inside the namespace for
+  // the original function and it is not in the global namespace.  The
+  // assumption is that outside the original namespace we must have a using
+  // statement that makes this work out and that other parts of this refactor
+  // will automatically fix using statements to point to the new function
+  const bool class_name_only = !Use;
+  const bool in_global_namespace =
+      isa<TranslationUnitDecl>(FromDecl->getDeclContext());
+  if (class_name_only && !in_global_namespace &&
+      !isInsideDifferentNamespaceWithSameName(FromDecl->getDeclContext(),
+                                              UseContext)) {
+    auto Pos = ReplacementString.rfind("::");
+    return Pos != StringRef::npos ? ReplacementString.substr(Pos + 2)
+                                  : ReplacementString;
+  }
+  // We did not match this because of a using statement, so we will need to
+  // figure out how good a namespace match we have with our destination type.
+  // We work backwards (from most specific possible namespace to least
+  // specific).
+  return getBestNamespaceSubstr(UseContext, ReplacementString,
+                                isFullyQualified(Use));
+}

unittests/Tooling/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS
   ${LLVM_TARGETS_TO_BUILD}
   Support
   )
 
 add_clang_unittest(ToolingTests
   CommentHandlerTest.cpp
   CompilationDatabaseTest.cpp
+  LookupTest.cpp
   ToolingTest.cpp
   RecursiveASTVisitorTest.cpp
   RecursiveASTVisitorTestCallVisitor.cpp
   RecursiveASTVisitorTestDeclVisitor.cpp
   RecursiveASTVisitorTestExprVisitor.cpp
   RecursiveASTVisitorTestTypeLocVisitor.cpp
   RefactoringTest.cpp
   RewriterTest.cpp

unittests/Tooling/LookupTest.cpp

+//===- unittest/Tooling/LookupTest.cpp ------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "TestVisitor.h"
+#include "clang/Tooling/Core/Lookup.h"
+using namespace clang;
+
+namespace {
+struct GetDeclsVisitor : TestVisitor<GetDeclsVisitor> {
+  std::function<void(CallExpr *)> OnCall;
+  SmallVector<Decl *, 4> DeclStack;
+
+  bool VisitCallExpr(CallExpr *Expr) {
+    OnCall(Expr);
+    return true;
+  }
+
+  bool TraverseDecl(Decl *D) {
+    DeclStack.push_back(D);
+    bool Ret = TestVisitor::TraverseDecl(D);
+    DeclStack.pop_back();
+    return Ret;
+  }
+};
+
+TEST(LookupTest, replaceNestedName) {
+  GetDeclsVisitor Visitor;
+
+  auto replaceCallExpr = [&](const CallExpr *Expr,
+                             StringRef ReplacementString) {
+    const auto *Callee = cast<DeclRefExpr>(Expr->getCallee()->IgnoreImplicit());
+    const ValueDecl *FD = Callee->getDecl();
+    return tooling::replaceNestedName(
+        Callee->getQualifier(), Visitor.DeclStack.back()->getDeclContext(), FD,
+        ReplacementString);
+  };
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("bar", replaceCallExpr(Expr, "bar"));
+  };
+  Visitor.runOver("namespace a { void foo(); }\n"
+                  "namespace a { void f() { foo(); } }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver("namespace a { void foo(); }\n"
+                  "namespace a { void f() { foo(); } }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("a::bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver("namespace a { void foo(); }\n"
+                  "namespace b { void f() { a::foo(); } }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("a::bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver("namespace a { void foo(); }\n"
+                  "namespace b { namespace a { void foo(); }\n"
+                  "void f() { a::foo(); } }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver("namespace a { namespace b { void foo(); }\n"
+                  "void f() { b::foo(); } }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("bar", replaceCallExpr(Expr, "bar"));
+  };
+  Visitor.runOver("void foo(); void f() { foo(); }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("::bar", replaceCallExpr(Expr, "bar"));
+  };
+  Visitor.runOver("void foo(); void f() { ::foo(); }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("a::bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver("namespace a { void foo(); }\nvoid f() { a::foo(); }\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("a::bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver("namespace a { int foo(); }\nauto f = a::foo();\n");
+
+  Visitor.OnCall = [&](CallExpr *Expr) {
+    EXPECT_EQ("bar", replaceCallExpr(Expr, "a::bar"));
+  };
+  Visitor.runOver(
+      "namespace a { int foo(); }\nusing a::foo;\nauto f = foo();\n");
+}
+
+} // end anonymous namespace