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 // This plugin is used by clang/test/Frontend/plugin-attribute tests.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "clang/AST/ASTContext.h"
  17 #include "clang/AST/Attr.h"
  18 #include "clang/Sema/ParsedAttr.h"
  19 #include "clang/Sema/Sema.h"
  20 #include "clang/Sema/SemaDiagnostic.h"
  21 #include "llvm/IR/Attributes.h"
  22 using namespace clang;
  23
  24 namespace {
  25
  26 struct ExampleAttrInfo : public ParsedAttrInfo {
  27   ExampleAttrInfo() {
  28     // Can take up to 15 optional arguments, to emulate accepting a variadic
  29     // number of arguments. This just illustrates how many arguments a
  30     // `ParsedAttrInfo` can hold, we will not use that much in this example.
  31     OptArgs = 15;
  32     // GNU-style __attribute__(("example")) and C++/C23-style [[example]] and
  33     // [[plugin::example]] supported.
  34     static constexpr Spelling S[] = {{ParsedAttr::AS_GNU, "example"},
  35                                      {ParsedAttr::AS_C23, "example"},
  36                                      {ParsedAttr::AS_CXX11, "example"},
  37                                      {ParsedAttr::AS_CXX11, "plugin::example"}};
  38     Spellings = S;
  39   }
  40
  41   bool diagAppertainsToDecl(Sema &S, const ParsedAttr &Attr,
  42                             const Decl *D) const override {
  43     // This attribute appertains to functions only.
  44     if (!isa<FunctionDecl>(D)) {
  45       S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type_str)
  46           << Attr << Attr.isRegularKeywordAttribute() << "functions";
  47       return false;
  48     }
  49     return true;
  50   }
  51
  52   AttrHandling handleDeclAttribute(Sema &S, Decl *D,
  53                                    const ParsedAttr &Attr) const override {
  54     // Check if the decl is at file scope.
  55     if (!D->getDeclContext()->isFileContext()) {
  56       unsigned ID = S.getDiagnostics().getCustomDiagID(
  57           DiagnosticsEngine::Error,
  58           "'example' attribute only allowed at file scope");
  59       S.Diag(Attr.getLoc(), ID);
  60       return AttributeNotApplied;
  61     }
  62     // We make some rules here:
  63     // 1. Only accept at most 3 arguments here.
  64     // 2. The first argument must be a string literal if it exists.
  65     if (Attr.getNumArgs() > 3) {
  66       unsigned ID = S.getDiagnostics().getCustomDiagID(
  67           DiagnosticsEngine::Error,
  68           "'example' attribute only accepts at most three arguments");
  69       S.Diag(Attr.getLoc(), ID);
  70       return AttributeNotApplied;
  71     }
  72     // If there are arguments, the first argument should be a string literal.
  73     if (Attr.getNumArgs() > 0) {
  74       auto *Arg0 = Attr.getArgAsExpr(0);
  75       StringLiteral *Literal =
  76           dyn_cast<StringLiteral>(Arg0->IgnoreParenCasts());
  77       if (!Literal) {
  78         unsigned ID = S.getDiagnostics().getCustomDiagID(
  79             DiagnosticsEngine::Error, "first argument to the 'example' "
  80                                       "attribute must be a string literal");
  81         S.Diag(Attr.getLoc(), ID);
  82         return AttributeNotApplied;
  83       }
  84       SmallVector<Expr *, 16> ArgsBuf;
  85       for (unsigned i = 0; i < Attr.getNumArgs(); i++) {
  86         ArgsBuf.push_back(Attr.getArgAsExpr(i));
  87       }
  88       D->addAttr(AnnotateAttr::Create(S.Context, "example", ArgsBuf.data(),
  89                                       ArgsBuf.size(), Attr.getRange()));
  90     } else {
  91       // Attach an annotate attribute to the Decl.
  92       D->addAttr(AnnotateAttr::Create(S.Context, "example", nullptr, 0,
  93                                       Attr.getRange()));
  94     }
  95     return AttributeApplied;
  96   }
  97 };
  98
  99 } // namespace
 100
 101 static ParsedAttrInfoRegistry::Add<ExampleAttrInfo> X("example", "");