template <typename Request, typename Response>
class BaseCgi {
public:
    BaseCgi(Request request, std::function<void(Response &)> &callback) {
        _request = request;
        _callback = callback;
    }

    void onRequest(std::vector<uint8_t> &outData) {
        _request.toData(outData);
    }

    void onResponse(std::vector<uint8_t> &inData) {
        Response response;
        response.fromData(inData);
        callback(response);
    }

public:
    Request _request;
    std::function<void(Response &)> _callback;
};

class CgiA : public BaseCgi<RequestA, ResponseA> {
public:
    CgiA(RequestA &request, std::function<void(ResponseA &)> &callback) :
        BaseCgi(request, callback) {}
};

class BaseRequest {
public:
    virtual void toData(std::vector<uint8_t> &outData) = 0;
};

class BaseResponse {
public:
    virtual void fromData(std::vector<uint8_t> &outData) = 0;
};

class BaseCgi {
public:
    template <typename Request, typename Response>
    BaseCgi(Request &request, hyper_function<void(Response &)> callback) {
        _request = new Request(request);
        _response = new Response;
        _callback = callback;
    }
    
    void onRequest(std::vector<uint8_t> &outData) {
        _request->toData(outData);
    }
    
    void onResponse(std::vector<uint8_t> &inData) {
        _response->fromData(inData);
        _callback(*_response);
    }
    
public:
    BaseRequest *_request;
    BaseResponse *_response;
    hyper_function<void(BaseResponse &)> _callback;
};

class RequestA : public BaseRequest { ... };

class ResponseA : public BaseResponse { ... };

class CgiA : public BaseCgi {
public:
    CgiA(RequestA &request, hyper_function<void(ResponseA &)> &callback) :
        BaseCgi(request, callback) {}
};

➜  clang -ccc-print-phases main.m
0: input, "main.m", objective-c
1: preprocessor, {0}, objective-c-cpp-output
2: compiler, {1}, ir
3: backend, {2}, assembler
4: assembler, {3}, object
5: linker, {4}, image
6: bind-arch, "x86_64", {5}, image

// HeaderA.h
struct StructA {
    int val;
};

// HeaderB.h
struct StructB {
    int val;
};

// main.c
#include "HeaderA.h"
#include "HeaderB.h"

int testAndReturn(struct StructA *a, struct StructB *b) {
    return a->val;
}

➜  TestContainer clang -Xclang -ast-dump -fsyntax-only main.c
TranslationUnitDecl 0x7f8f36834208 <<invalid sloc>> <invalid sloc>
|-RecordDecl 0x7faa62831d78 <./HeaderA.h:12:1, line:14:1> line:12:8 struct StructA definition
| `-FieldDecl 0x7faa6383da38 <line:13:2, col:6> col:6 referenced val 'int'
|-RecordDecl 0x7faa6383da80 <./HeaderB.h:12:1, line:14:1> line:12:8 struct StructB definition
| `-FieldDecl 0x7faa6383db38 <line:13:2, col:6> col:6 val 'int'
`-FunctionDecl 0x7faa6383de50 <main.c:35:1, line:37:1> line:35:5 testAndReturn 'int (struct StructA *, struct StructB *)'
  |-ParmVarDecl 0x7faa6383dc30 <col:19, col:35> col:35 used a 'struct StructA *'
  |-ParmVarDecl 0x7faa6383dd40 <col:38, col:54> col:54 b 'struct StructB *'
  `-CompoundStmt 0x7faa6383dfc8 <col:57, line:37:1>
    `-ReturnStmt 0x7faa6383dfb8 <line:36:2, col:12>
      `-ImplicitCastExpr 0x7faa6383dfa0 <col:9, col:12> 'int' <LValueToRValue>
        `-MemberExpr 0x7faa6383df70 <col:9, col:12> 'int' lvalue ->val 0x7faa6383da38
          `-ImplicitCastExpr 0x7faa6383df58 <col:9> 'struct StructA *' <LValueToRValue>
            `-DeclRefExpr 0x7faa6383df38 <col:9> 'struct StructA *' lvalue ParmVar 0x7faa6383dc30 'a' 'struct StructA *'

class MyFrontendAction : public clang::ASTFrontendAction {
public:
    virtual std::unique_ptr<clang::ASTConsumer> CreateASTConsumer(clang::CompilerInstance &CI, llvm::StringRef file) override {
        TheRewriter.setSourceMgr(CI.getASTContext().getSourceManager(), CI.getASTContext().getLangOpts());
        return llvm::make_unique<MyASTConsumer>(&CI);
    }
};

int main(int argc, const char **argv) {
    clang::tooling::CommonOptionsParser op(argc, argv, OptsCategory);
    clang::tooling::ClangTool Tool(op.getCompilations(), op.getSourcePathList());
    int result = Tool.run(clang::tooling::newFrontendActionFactory<MyFrontendAction>().get());

    return result;
}

class MyASTVisitor
: public clang::RecursiveASTVisitor<MyASTVisitor> {
public:
    explicit MyASTVisitor(clang::ASTContext *Ctx) {}
    
    bool VisitFunctionDecl(clang::FunctionDecl* decl) {
        // FunctionDecl 下的所有参数声明允许前置声明取代 include
        // 如上面 Demo 代码里 StructA、StructB
        return true;
    }
    
    bool VisitMemberExpr(clang::MemberExpr* expr) {
        // 被引用的成员所在的类，需要 include 它定义所在文件
        // 如 StructA
        return true;
    }

    bool VisitXXX(XXX) {
        return true;
    }
    
    // 同一个类型，可能出现若干次判定结果
    // 如果其中一个判断的结果需要 include，则 include
    // 否则使用前置声明代替 include
    // 例如 StructA 只能 include，StructB 可以前置声明
};

class MyASTConsumer : public clang::ASTConsumer {
private:
    MyASTVisitor Visitor;
public:
    explicit MyASTConsumer(clang::CompilerInstance *aCI)
    : Visitor(&(aCI->getASTContext())) {}
    
    void HandleTranslationUnit(clang::ASTContext &context) override {
        clang::TranslationUnitDecl *decl = context.getTranslationUnitDecl();
        Visitor.TraverseTranslationUnitDecl(decl);
    }
};

➜  include-what-you-use main.c
HeaderA.h has correct #includes/fwd-decls)

HeaderB.h has correct #includes/fwd-decls)

main.c should add these lines:
struct StructB;

main.c should remove these lines:
- #include "HeaderB.h"  // lines 2-2

The full include-list for main.c:
#include "HeaderA.h"  // for StructA
struct StructB;