clang/examples/Attribute/Attribute.cpp

   1 //===- Attribute.cpp ------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Example clang plugin which adds an an annotation to file-scope declarations
  10 // with the 'example' attribute.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "clang/AST/ASTContext.h"
  15 #include "clang/AST/Attr.h"
  16 #include "clang/Sema/ParsedAttr.h"
  17 #include "clang/Sema/Sema.h"
  18 #include "clang/Sema/SemaDiagnostic.h"
  19 #include "llvm/IR/Attributes.h"
  20 using namespace clang;
  21
  22 namespace {
  23
  24 struct ExampleAttrInfo : public ParsedAttrInfo {
  25   ExampleAttrInfo() {
  26     // Can take up to 15 optional arguments, to emulate accepting a variadic
  27     // number of arguments. This just illustrates how many arguments a
  28     // `ParsedAttrInfo` can hold, we will not use that much in this example.
  29     OptArgs = 15;
  30     // GNU-style __attribute__(("example")) and C++-style [[example]] and
  31     // [[plugin::example]] supported.
  32     static constexpr Spelling S[] = {{ParsedAttr::AS_GNU, "example"},
  33                                      {ParsedAttr::AS_CXX11, "example"},
  34                                      {ParsedAttr::AS_CXX11, "plugin::example"}};
  35     Spellings = S;
  36   }
  37
  38   bool diagAppertainsToDecl(Sema &S, const ParsedAttr &Attr,
  39                             const Decl *D) const override {
  40     // This attribute appertains to functions only.
  41     if (!isa<FunctionDecl>(D)) {
  42       S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type_str)
  43           << Attr << "functions";
  44       return false;
  45     }
  46     return true;
  47   }
  48
  49   AttrHandling handleDeclAttribute(Sema &S, Decl *D,
  50                                    const ParsedAttr &Attr) const override {
  51     // Check if the decl is at file scope.
  52     if (!D->getDeclContext()->isFileContext()) {
  53       unsigned ID = S.getDiagnostics().getCustomDiagID(
  54           DiagnosticsEngine::Error,
  55           "'example' attribute only allowed at file scope");
  56       S.Diag(Attr.getLoc(), ID);
  57       return AttributeNotApplied;
  58     }
  59     // We make some rules here:
  60     // 1. Only accept at most 3 arguments here.
  61     // 2. The first argument must be a string literal if it exists.
  62     if (Attr.getNumArgs() > 3) {
  63       unsigned ID = S.getDiagnostics().getCustomDiagID(
  64           DiagnosticsEngine::Error,
  65           "'example' attribute only accepts at most three arguments");
  66       S.Diag(Attr.getLoc(), ID);
  67       return AttributeNotApplied;
  68     }
  69     // If there are arguments, the first argument should be a string literal.
  70     if (Attr.getNumArgs() > 0) {
  71       auto *Arg0 = Attr.getArgAsExpr(0);
  72       StringLiteral *Literal =
  73           dyn_cast<StringLiteral>(Arg0->IgnoreParenCasts());
  74       if (!Literal) {
  75         unsigned ID = S.getDiagnostics().getCustomDiagID(
  76             DiagnosticsEngine::Error, "first argument to the 'example' "
  77                                       "attribute must be a string literal");
  78         S.Diag(Attr.getLoc(), ID);
  79         return AttributeNotApplied;
  80       }
  81       SmallVector<Expr *, 16> ArgsBuf;
  82       for (unsigned i = 0; i < Attr.getNumArgs(); i++) {
  83         ArgsBuf.push_back(Attr.getArgAsExpr(i));
  84       }
  85       D->addAttr(AnnotateAttr::Create(S.Context, "example", ArgsBuf.data(),
  86                                       ArgsBuf.size(), Attr.getRange()));
  87     } else {
  88       // Attach an annotate attribute to the Decl.
  89       D->addAttr(AnnotateAttr::Create(S.Context, "example", nullptr, 0,
  90                                       Attr.getRange()));
  91     }
  92     return AttributeApplied;
  93   }
  94 };
  95
  96 } // namespace
  97
  98 static ParsedAttrInfoRegistry::Add<ExampleAttrInfo> X("example", "");