[docs] Use make_unique in FrontendAction example

[nicolas17]

Summary

The code example for "RecursiveASTVisitor based ASTFrontendActions"
was using unique_ptr<X>(new X) when creating the AST consumer; change
it to use make_unique instead. The main function of the same example
already used make_unique.

[nicolas17]

I don't have commit access, please push this for me.

[dblaikie]

@thakis - just FYI, Phab doesn't send mail to the mailing list when a patch is approved without any text. Please include some text when approving patches to make sure there's a record on the mailing list. (@MaskRay has a browser script or the like to automate this - I forget if it's posted somewhere to link to... maybe in the llvm phab docs)

[MaskRay]

In D93185#2688003, @dblaikie wrote:

@thakis - just FYI, Phab doesn't send mail to the mailing list when a patch is approved without any text. Please include some text when approving patches to make sure there's a record on the mailing list. (@MaskRay has a browser script or the like to automate this - I forget if it's posted somewhere to link to... maybe in the llvm phab docs)

Only use in trivial approvals :)

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// @name         reviews.llvm.org: add comment "LGTM" when accepting
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        if (comment && comment.value.length == 0) {
          const words = ['LGTM.', 'Thanks!', 'Looks great!']
          comment.value = words[~~(Math.random()*words.length)]+' '
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clang/docs/RAVFrontendAction.rst

 unit.
 
 ::
 
       class FindNamedClassAction : public clang::ASTFrontendAction {
       public:
         virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer(
           clang::CompilerInstance &Compiler, llvm::StringRef InFile) {
-          return std::unique_ptr<clang::ASTConsumer>(
-              new FindNamedClassConsumer);
+          return std::make_unique<FindNamedClassConsumer>();
         }
       };
 
 Creating an ASTConsumer
 =======================
 
 ASTConsumer is an interface used to write generic actions on an AST,
 regardless of how the AST was produced. ASTConsumer provides many

 The ASTContext is available from the CompilerInstance during the call to
 CreateASTConsumer. We can thus extract it there and hand it into our
 freshly created FindNamedClassConsumer:
 
 ::
 
       virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer(
         clang::CompilerInstance &Compiler, llvm::StringRef InFile) {
-        return std::unique_ptr<clang::ASTConsumer>(
-            new FindNamedClassConsumer(&Compiler.getASTContext()));
+        return std::make_unique<FindNamedClassConsumer>(&Compiler.getASTContext());
       }
 
 Now that the ASTContext is available in the RecursiveASTVisitor, we can
 do more interesting things with AST nodes, like looking up their source
 locations:
 
 ::
 
::
       private:
         FindNamedClassVisitor Visitor;
       };
 
       class FindNamedClassAction : public clang::ASTFrontendAction {
       public:
         virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer(
           clang::CompilerInstance &Compiler, llvm::StringRef InFile) {
-          return std::unique_ptr<clang::ASTConsumer>(
-              new FindNamedClassConsumer(&Compiler.getASTContext()));
+          return std::make_unique<FindNamedClassConsumer>(&Compiler.getASTContext());
         }
       };
 
       int main(int argc, char **argv) {
         if (argc > 1) {
           clang::tooling::runToolOnCode(std::make_unique<FindNamedClassAction>(), argv[1]);
         }
       }