[libTooling] Add `describe` combinator for formatting AST nodes for diagnostics.

This new stencil combinator is intended for use in diagnostics and the like.

Differential Revision: https://reviews.llvm.org/D92658

clang/include/clang/Tooling/Transformer/Stencil.h

@@ -123,6 +123,15 @@ inline Stencil ifBound(llvm::StringRef Id, llvm::StringRef TrueText,
 /// Stencil.  This supports user-defined extensions to the \c Stencil language.
 Stencil run(MatchConsumer<std::string> C);
 
+/// Produces a human-readable rendering of the node bound to `Id`, suitable for
+/// diagnostics and debugging. This operator can be applied to any node, but is
+/// targeted at those whose source cannot be printed directly, including:
+///
+/// * Types. represented based on their structure. Note that namespace
+///   qualifiers are always printed, with the anonymous namespace represented
+///   explicitly. No desugaring or canonicalization is applied.
+Stencil describe(llvm::StringRef Id);
+
 /// For debug use only; semantics are not guaranteed.
 ///
 /// \returns the string resulting from calling the node's print() method.

clang/lib/Tooling/Transformer/Stencil.cpp

@@ -63,6 +63,7 @@ enum class UnaryNodeOperator {
   MaybeDeref,
   AddressOf,
   MaybeAddressOf,
+  Describe,
 };
 
 // Generic container for stencil operations with a (single) node-id argument.
@@ -133,6 +134,9 @@ std::string toStringData(const UnaryOperationData &Data) {
   case UnaryNodeOperator::MaybeAddressOf:
     OpName = "maybeAddressOf";
     break;
+  case UnaryNodeOperator::Describe:
+    OpName = "describe";
+    break;
   }
   return (OpName + "(\"" + Data.Id + "\")").str();
 }
@@ -174,11 +178,11 @@ Error evalData(const RawTextData &Data, const MatchFinder::MatchResult &,
   return Error::success();
 }
 
-Error evalData(const DebugPrintNodeData &Data,
-               const MatchFinder::MatchResult &Match, std::string *Result) {
+static Error printNode(StringRef Id, const MatchFinder::MatchResult &Match,
+                       std::string *Result) {
   std::string Output;
   llvm::raw_string_ostream Os(Output);
-  auto NodeOrErr = getNode(Match.Nodes, Data.Id);
+  auto NodeOrErr = getNode(Match.Nodes, Id);
   if (auto Err = NodeOrErr.takeError())
     return Err;
   NodeOrErr->print(Os, PrintingPolicy(Match.Context->getLangOpts()));
@@ -186,8 +190,18 @@ Error evalData(const DebugPrintNodeData &Data,
   return Error::success();
 }
 
+Error evalData(const DebugPrintNodeData &Data,
+               const MatchFinder::MatchResult &Match, std::string *Result) {
+  return printNode(Data.Id, Match, Result);
+}
+
 Error evalData(const UnaryOperationData &Data,
                const MatchFinder::MatchResult &Match, std::string *Result) {
+  // The `Describe` operation can be applied to any node, not just expressions,
+  // so it is handled here, separately.
+  if (Data.Op == UnaryNodeOperator::Describe)
+    return printNode(Data.Id, Match, Result);
+
   const auto *E = Match.Nodes.getNodeAs<Expr>(Data.Id);
   if (E == nullptr)
     return llvm::make_error<StringError>(
@@ -217,6 +231,8 @@ Error evalData(const UnaryOperationData &Data,
     }
     Source = tooling::buildAddressOf(*E, *Match.Context);
     break;
+  case UnaryNodeOperator::Describe:
+    llvm_unreachable("This case is handled at the start of the function");
   }
   if (!Source)
     return llvm::make_error<StringError>(
@@ -359,6 +375,11 @@ Stencil transformer::maybeAddressOf(llvm::StringRef ExprId) {
       UnaryNodeOperator::MaybeAddressOf, std::string(ExprId));
 }
 
+Stencil transformer::describe(StringRef Id) {
+  return std::make_shared<StencilImpl<UnaryOperationData>>(
+      UnaryNodeOperator::Describe, std::string(Id));
+}
+
 Stencil transformer::access(StringRef BaseId, Stencil Member) {
   return std::make_shared<StencilImpl<AccessData>>(BaseId, std::move(Member));
 }

clang/unittests/Tooling/StencilTest.cpp

@@ -30,7 +30,9 @@ using MatchResult = MatchFinder::MatchResult;
 
 // Create a valid translation-unit from a statement.
 static std::string wrapSnippet(StringRef StatementCode) {
-  return ("struct S { int field; }; auto stencil_test_snippet = []{" +
+  return ("namespace N { class C {}; } "
+          "namespace { class AnonC {}; } "
+          "struct S { int field; }; auto stencil_test_snippet = []{" +
           StatementCode + "};")
       .str();
 }
@@ -55,14 +57,14 @@ struct TestMatch {
 // `StatementCode` may contain other statements not described by `Matcher`.
 static llvm::Optional<TestMatch> matchStmt(StringRef StatementCode,
                                            StatementMatcher Matcher) {
-  auto AstUnit = tooling::buildASTFromCode(wrapSnippet(StatementCode));
+  auto AstUnit = tooling::buildASTFromCodeWithArgs(wrapSnippet(StatementCode),
+                                                   {"-Wno-unused-value"});
   if (AstUnit == nullptr) {
     ADD_FAILURE() << "AST construction failed";
     return llvm::None;
   }
   ASTContext &Context = AstUnit->getASTContext();
-  auto Matches = ast_matchers::match(
-      traverse(ast_type_traits::TK_AsIs, wrapMatcher(Matcher)), Context);
+  auto Matches = ast_matchers::match(wrapMatcher(Matcher), Context);
   // We expect a single, exact match for the statement.
   if (Matches.size() != 1) {
     ADD_FAILURE() << "Wrong number of matches: " << Matches.size();
@@ -365,6 +367,66 @@ TEST_F(StencilTest, AccessOpImplicitThis) {
   EXPECT_THAT_EXPECTED(Stencil->eval(StmtMatch->Result), HasValue("field"));
 }
 
+TEST_F(StencilTest, DescribeType) {
+  std::string Snippet = "int *x; x;";
+  std::string Expected = "int *";
+  auto StmtMatch =
+      matchStmt(Snippet, declRefExpr(hasType(qualType().bind("type"))));
+  ASSERT_TRUE(StmtMatch);
+  EXPECT_THAT_EXPECTED(describe("type")->eval(StmtMatch->Result),
+                       HasValue(std::string(Expected)));
+}
+
+TEST_F(StencilTest, DescribeSugaredType) {
+  std::string Snippet = "using Ty = int; Ty *x; x;";
+  std::string Expected = "Ty *";
+  auto StmtMatch =
+      matchStmt(Snippet, declRefExpr(hasType(qualType().bind("type"))));
+  ASSERT_TRUE(StmtMatch);
+  EXPECT_THAT_EXPECTED(describe("type")->eval(StmtMatch->Result),
+                       HasValue(std::string(Expected)));
+}
+
+TEST_F(StencilTest, DescribeDeclType) {
+  std::string Snippet = "S s; s;";
+  std::string Expected = "S";
+  auto StmtMatch =
+      matchStmt(Snippet, declRefExpr(hasType(qualType().bind("type"))));
+  ASSERT_TRUE(StmtMatch);
+  EXPECT_THAT_EXPECTED(describe("type")->eval(StmtMatch->Result),
+                       HasValue(std::string(Expected)));
+}
+
+TEST_F(StencilTest, DescribeQualifiedType) {
+  std::string Snippet = "N::C c; c;";
+  std::string Expected = "N::C";
+  auto StmtMatch =
+      matchStmt(Snippet, declRefExpr(hasType(qualType().bind("type"))));
+  ASSERT_TRUE(StmtMatch);
+  EXPECT_THAT_EXPECTED(describe("type")->eval(StmtMatch->Result),
+                       HasValue(std::string(Expected)));
+}
+
+TEST_F(StencilTest, DescribeUnqualifiedType) {
+  std::string Snippet = "using N::C; C c; c;";
+  std::string Expected = "N::C";
+  auto StmtMatch =
+      matchStmt(Snippet, declRefExpr(hasType(qualType().bind("type"))));
+  ASSERT_TRUE(StmtMatch);
+  EXPECT_THAT_EXPECTED(describe("type")->eval(StmtMatch->Result),
+                       HasValue(std::string(Expected)));
+}
+
+TEST_F(StencilTest, DescribeAnonNamespaceType) {
+  std::string Snippet = "AnonC c; c;";
+  std::string Expected = "(anonymous namespace)::AnonC";
+  auto StmtMatch =
+      matchStmt(Snippet, declRefExpr(hasType(qualType().bind("type"))));
+  ASSERT_TRUE(StmtMatch);
+  EXPECT_THAT_EXPECTED(describe("type")->eval(StmtMatch->Result),
+                       HasValue(std::string(Expected)));
+}
+
 TEST_F(StencilTest, RunOp) {
   StringRef Id = "id";
   auto SimpleFn = [Id](const MatchResult &R) {
@@ -436,6 +498,12 @@ TEST_F(StencilTest, CatOfInvalidRangeFails) {
   });
 }
 
+// The `StencilToStringTest` tests verify that the string representation of the
+// stencil combinator matches (as best possible) the spelling of the
+// combinator's construction.  Exceptions include those combinators that have no
+// explicit spelling (like raw text) and those supporting non-printable
+// arguments (like `run`, `selection`).
+
 TEST(StencilToStringTest, RawTextOp) {
   auto S = cat("foo bar baz");
   StringRef Expected = R"("foo bar baz")";
@@ -448,6 +516,12 @@ TEST(StencilToStringTest, RawTextOpEscaping) {
   EXPECT_EQ(S->toString(), Expected);
 }
 
+TEST(StencilToStringTest, DescribeOp) {
+  auto S = describe("Id");
+  StringRef Expected = R"repr(describe("Id"))repr";
+  EXPECT_EQ(S->toString(), Expected);
+}
+
 TEST(StencilToStringTest, DebugPrintNodeOp) {
   auto S = dPrint("Id");
   StringRef Expected = R"repr(dPrint("Id"))repr";