clang - libclang:在 AST 中缺少一些语句？

Question

我写了一个测试程序(parse_ast.c)来解析一个c源文件(tt.c)来看看libclang是如何工作的，输出是AST的层次结构:

这是测试文件:

/* tt.c */                                    // line 1
#include <unistd.h>
#include <stdio.h>

typedef ssize_t (*write_fn_t)(int, const void *, size_t);

void indirect_write(write_fn_t write_fn) {    // line 7
    (*write_fn)(1, "indirect call\n", 14);
}

void direct_write() {                         // line 11
    write(1, "direct call\n", 12);            // line 12 mising in the ast?
}

int main() {                                  // line 15
    direct_write();
    indirect_write(write);                    // line 17 missing in the ast?

    return 0;
}

输出显示如下:

 ...
 ...
 inclusion directive at tt.c (2, 1) to (2, 20)
 inclusion directive at tt.c (3, 1) to (3, 19)
 TypedefDecl at tt.c (5, 1) to (5, 57)
 TypeRef at tt.c (5, 9) to (5, 16)
 ParmDecl at tt.c (5, 31) to (5, 35)
 ParmDecl at tt.c (5, 36) to (5, 49)
 ParmDecl at tt.c (5, 50) to (5, 56)
 FunctionDecl at tt.c (7, 1) to (9, 2)
 ParmDecl at tt.c (7, 21) to (7, 40)
  TypeRef at tt.c (7, 21) to (7, 31)
 CompoundStmt at tt.c (7, 42) to (9, 2)
  CallExpr at tt.c (8, 5) to (8, 42)
   UnexposedExpr at tt.c (8, 5) to (8, 16)
    ParenExpr at tt.c (8, 5) to (8, 16)
     UnaryOperator at tt.c (8, 6) to (8, 15)
      UnexposedExpr at tt.c (8, 7) to (8, 15)
       DeclRefExpr at tt.c (8, 7) to (8, 15)
   IntegerLiteral at tt.c (8, 17) to (8, 18)
   UnexposedExpr at tt.c (8, 20) to (8, 37)
    UnexposedExpr at tt.c (8, 20) to (8, 37)
     StringLiteral at tt.c (8, 20) to (8, 37)
   IntegerLiteral at tt.c (8, 39) to (8, 41)
 FunctionDecl at tt.c (11, 1) to (13, 2)
 CompoundStmt at tt.c (11, 21) to (13, 2)        <- XXX no line 12?
 FunctionDecl at tt.c (15, 1) to (20, 2)
 CompoundStmt at tt.c (15, 12) to (20, 2)
  CallExpr at tt.c (16, 5) to (16, 19)
   UnexposedExpr at tt.c (16, 5) to (16, 17)
    DeclRefExpr at tt.c (16, 5) to (16, 17)      <- XXX no line 17?
  ReturnStmt at tt.c (19, 5) to (19, 13)
   IntegerLiteral at tt.c (19, 12) to (19, 13)

我们可以看到三个函数(第 7 行的 direct_write/第 11 行的 indirect_write/第 15 行的 main)都在那里，大多数语句都可以在 AST 中找到，但我找不到任何代表第 12 行语句的东西，第 17 行。有人知道原因吗？

我在 debian 2.6.32 上，在 clang 3.1 和 3.2(从源代码编译)上进行了测试。

这是程序 parse_ast.c:

#include <stddef.h>
#include <stdio.h>
#include <clang-c/Index.h>

enum CXChildVisitResult visit_fn(CXCursor cr, CXCursor parent,
        CXClientData client_data) {

    unsigned depth;
    unsigned line, column, offset;
    enum CXCursorKind kind;
    CXSourceRange extent;
    CXSourceLocation start, end;
    CXString kind_spelling, filename;
    CXFile file;

    depth = (unsigned)client_data;

    // print cursor kind
    kind = clang_getCursorKind(cr);
    kind_spelling = clang_getCursorKindSpelling(kind);
    fprintf(stdout, "%*s%s at", depth, " ", clang_getCString(kind_spelling));
    clang_disposeString(kind_spelling);

    // get extent
    extent = clang_getCursorExtent(cr);
    start = clang_getRangeStart(extent);
    end = clang_getRangeEnd(extent);

    // print start position
    clang_getExpansionLocation(start, &file, &line, &column, &offset);
    filename = clang_getFileName(file);
    fprintf(stdout, " %s (%u, %u) to", clang_getCString(filename), line,
            column);
    clang_disposeString(filename);

    // print end position
    clang_getExpansionLocation(end, &file, &line, &column, &offset);
    fprintf(stdout, " (%u, %u)\n", line, column);

    // recursive
    clang_visitChildren(cr, visit_fn, (CXClientData)(depth + 1));

    return CXChildVisit_Continue;

}

int main(int argc, const char * const *argv) {
    CXIndex Index = clang_createIndex(0, 0);
    CXTranslationUnit TU = clang_parseTranslationUnit(Index, NULL,
            argv, argc, 0, 0, CXTranslationUnit_DetailedPreprocessingRecord);

    clang_visitChildren(clang_getTranslationUnitCursor(TU),
            visit_fn, 0);
    clang_disposeTranslationUnit(TU);
    clang_disposeIndex(Index);

    return 0;
}

更新 :

问题是由于缺少头文件 stddef.h，它在 libclang 的邮件列表中得到了回答 http://clang-developers.42468.n3.nabble.com/libclang-missing-some-statements-in-the-AST-td4029641.html

Answer 1

检查 clang_parseTranslationUnit() 生成的诊断信息- 即使遇到错误，也会生成 AST，但显然不能保证它是有意义的。

我发现注释掉了 #include行导致编译错误，但生成了一个类似于您的 AST(特别是第 17 行丢失)。

更换 #include带有用于 size_t 的 typedef 的行和 ssize_t (如 int )导致关于 write() 的隐式声明的编译警告，但 AST 包括第 17 行。

因此，我假设您的头文件中存在问题，诊断应显示该问题。
诊断可以通过例如检索

for (unsigned I = 0, N = clang_getNumDiagnostics(TU); I != N; ++I) { 
    CXDiagnostic Diag = clang_getDiagnostic(TU, I);
    CXString String = clang_formatDiagnostic(Diag, clang_defaultDiagnosticDisplayOptions());
    fprintf(stderr, "%s\n", clang_getCString(String));
    clang_disposeString(String);
}