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", "");
99