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<p>I have found the AST Matcher Reference to be useful while developing matchers: <a href="http://clang.llvm.org/docs/LibASTMatchersReference.html">http://clang.llvm.org/docs/LibASTMatchersReference.html</a><br>
</p>
<p><br>
</p>
<p>Instead of writing your own debug matcher you may want to try clang-query.<br>
</p>
<p>I don't think it's documented yet but it's quite straightforward to get started. You will have an interactive shell session to build your matcher and see the results in live, I tried it the other day and I suggest to use it with libedit support so it will
complete for you the possible matchers as you type.<br>
</p>
<p><br>
</p>
<p><a href="https://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-query/" title="https://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-query/
Ctrl+click or tap to follow link">https://llvm.org/viewvc/llvm-project/clang-tools-extra/trunk/clang-query/</a><br>
</p>
<p><br>
</p>
<p>To generate the AST dump you may want to use clang-check instead of clang++ with all the arguments. clang-check allows you to filter the AST and remove the need of specifying things like -fsyntax-only.<br>
</p>
<p><br>
</p>
<p>I have found the ast-dump useful since it provides the names of the types that you can look for in the AST Matcher Reference.<br>
</p>
<p><br>
</p>
<div style="color: #282828;">
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size: 11pt;"><b>From:</b> Stephen Kelly <steveire@gmail.com><br>
<b>Sent:</b> 11 March 2014 10:48<br>
<b>To:</b> cfe-dev@cs.uiuc.edu<br>
<b>Subject:</b> [cfe-dev] How to write a matcher?</font>
<div> </div>
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<font size="2"><span style="font-size: 10pt;">
<div class="PlainText"><br>
Hi,<br>
<br>
I want to write a tool to remove c_str() calls in lines like<br>
<br>
std::cout << s.c_str();<br>
<br>
There isn't really enough information about what matchers mean, and how to <br>
use them. <br>
<br>
There is no good information on how to write/debug them, and how they need <br>
to be arranged (nested, in an allof, wrapped with to(), on(), callee() etc).<br>
<br>
How does one *actually* go about doing it?<br>
<br>
Here's my attempt:<br>
<br>
My test code is:<br>
<br>
int main(int, char **)<br>
{<br>
std::string s("something");<br>
std::cout << s << std::endl;<br>
std::cout << s.c_str() << std::endl;<br>
return 0;<br>
}<br>
<br>
I used<br>
<br>
clang++ -Xclang -ast-dump -fsyntax-only -fno-color-diagnostics ../main.cpp <br>
<br>
to generate <br>
<br>
`-FunctionDecl 0x275cae0 <../main.cpp:9:1, line:16:1> main 'int (int, char <br>
**)'<br>
|-ParmVarDecl 0x275c9a0 <line:9:10> 'int'<br>
|-ParmVarDecl 0x275ca10 <col:15, col:21> 'char **'<br>
`-CompoundStmt 0x275f150 <line:10:1, line:16:1><br>
|-DeclStmt 0x275d160 <line:11:3, col:23><br>
| `-VarDecl 0x275cc30 <col:3, col:22> s 'std::string':'class <br>
std::basic_string<char>'<br>
| `-ExprWithCleanups 0x275d148 <col:15, col:22> 'std::string':'class <br>
std::basic_string<char>'<br>
| `-CXXConstructExpr 0x275d108 <col:15, col:22> <br>
'std::string':'class std::basic_string<char>' 'void (const char *, const <br>
class std::allocator<char> &)'<br>
| |-ImplicitCastExpr 0x275cd20 <col:17> 'const char *' <br>
<ArrayToPointerDecay><br>
| | `-StringLiteral 0x275cc88 <col:17> 'const char [4]' lvalue <br>
"wtf"<br>
| `-CXXDefaultArgExpr 0x275d0e0 <<invalid sloc>> 'const class <br>
std::allocator<char>':'const class std::allocator<char>' lvalue<br>
|-CXXOperatorCallExpr 0x275e160 <line:12:3, col:26> <br>
'__ostream_type':'class std::basic_ostream<char>' lvalue<br>
| |-ImplicitCastExpr 0x275e148 <col:18> '__ostream_type &(*)<br>
(__ostream_type &(*)(__ostream_type &))' <FunctionToPointerDecay><br>
| | `-DeclRefExpr 0x275e0c0 <col:18> '__ostream_type &(__ostream_type <br>
&(*)(__ostream_type &))' lvalue CXXMethod 0x26d0410 'operator<<' <br>
'__ostream_type &(__ostream_type &(*)(__ostream_type &))'<br>
| |-CXXOperatorCallExpr 0x275d5c0 <col:3, col:16> 'basic_ostream<char, <br>
struct std::char_traits<char> >':'class std::basic_ostream<char>' lvalue<br>
| | |-ImplicitCastExpr 0x275d5a8 <col:13> 'basic_ostream<char, struct <br>
std::char_traits<char> > &(*)(basic_ostream<char, struct <br>
std::char_traits<char> > &, const basic_string<char, struct <br>
std::char_traits<char>, class std::allocator<char> > &)' <br>
<FunctionToPointerDecay><br>
| | | `-DeclRefExpr 0x275d528 <col:13> 'basic_ostream<char, struct <br>
std::char_traits<char> > &(basic_ostream<char, struct std::char_traits<char> <br>
> &, const basic_string<char, struct std::char_traits<char>, class <br>
std::allocator<char> > &)' lvalue Function 0x2533250 'operator<<' <br>
'basic_ostream<char, struct std::char_traits<char> > &(basic_ostream<char, <br>
struct std::char_traits<char> > &, const basic_string<char, struct <br>
std::char_traits<char>, class std::allocator<char> > &)'<br>
| | |-DeclRefExpr 0x275d198 <col:3, col:8> 'ostream':'class <br>
std::basic_ostream<char>' lvalue Var 0x275c3a0 'cout' 'ostream':'class <br>
std::basic_ostream<char>'<br>
| | `-ImplicitCastExpr 0x275d510 <col:16> 'const basic_string<char, <br>
struct std::char_traits<char>, class std::allocator<char> >':'const class <br>
std::basic_string<char>' lvalue <NoOp><br>
| | `-DeclRefExpr 0x275d1d0 <col:16> 'std::string':'class <br>
std::basic_string<char>' lvalue Var 0x275cc30 's' 'std::string':'class <br>
std::basic_string<char>'<br>
| `-ImplicitCastExpr 0x275e0a8 <col:21, col:26> 'basic_ostream<char, <br>
struct std::char_traits<char> > &(*)(basic_ostream<char, struct <br>
std::char_traits<char> > &)' <FunctionToPointerDecay><br>
| `-DeclRefExpr 0x275e068 <col:21, col:26> 'basic_ostream<char, <br>
struct std::char_traits<char> > &(basic_ostream<char, struct <br>
std::char_traits<char> > &)' lvalue Function 0x26d4480 'endl' <br>
'basic_ostream<char, struct std::char_traits<char> > &(basic_ostream<char, <br>
struct std::char_traits<char> > &)' (FunctionTemplate 0x26b9180 'endl')<br>
|-CXXOperatorCallExpr 0x275f0c8 <line:13:3, col:34> <br>
'__ostream_type':'class std::basic_ostream<char>' lvalue<br>
| |-ImplicitCastExpr 0x275f0b0 <col:26> '__ostream_type &(*)<br>
(__ostream_type &(*)(__ostream_type &))' <FunctionToPointerDecay><br>
| | `-DeclRefExpr 0x275f088 <col:26> '__ostream_type &(__ostream_type <br>
&(*)(__ostream_type &))' lvalue CXXMethod 0x26d0410 'operator<<' <br>
'__ostream_type &(__ostream_type &(*)(__ostream_type &))'<br>
| |-CXXOperatorCallExpr 0x275e610 <col:3, col:24> 'basic_ostream<char, <br>
struct std::char_traits<char> >':'class std::basic_ostream<char>' lvalue<br>
| | |-ImplicitCastExpr 0x275e5f8 <col:13> 'basic_ostream<char, struct <br>
std::char_traits<char> > &(*)(basic_ostream<char, struct <br>
std::char_traits<char> > &, const char *)' <FunctionToPointerDecay><br>
| | | `-DeclRefExpr 0x275e578 <col:13> 'basic_ostream<char, struct <br>
std::char_traits<char> > &(basic_ostream<char, struct std::char_traits<char> <br>
> &, const char *)' lvalue Function 0x26d9830 'operator<<' <br>
'basic_ostream<char, struct std::char_traits<char> > &(basic_ostream<char, <br>
struct std::char_traits<char> > &, const char *)'<br>
| | |-DeclRefExpr 0x275e1c8 <col:3, col:8> 'ostream':'class <br>
std::basic_ostream<char>' lvalue Var 0x275c3a0 'cout' 'ostream':'class <br>
std::basic_ostream<char>'<br>
| | `-CXXMemberCallExpr 0x275e258 <col:16, col:24> 'const char *'<br>
| | `-MemberExpr 0x275e228 <col:16, col:18> '<bound member function <br>
type>' .c_str 0x252c400<br>
| | `-ImplicitCastExpr 0x275e280 <col:16> 'const class <br>
std::basic_string<char>' lvalue <NoOp><br>
| | `-DeclRefExpr 0x275e200 <col:16> 'std::string':'class <br>
std::basic_string<char>' lvalue Var 0x275cc30 's' 'std::string':'class <br>
std::basic_string<char>'<br>
| `-ImplicitCastExpr 0x275f070 <col:29, col:34> 'basic_ostream<char, <br>
struct std::char_traits<char> > &(*)(basic_ostream<char, struct <br>
std::char_traits<char> > &)' <FunctionToPointerDecay><br>
| `-DeclRefExpr 0x275f030 <col:29, col:34> 'basic_ostream<char, <br>
struct std::char_traits<char> > &(basic_ostream<char, struct <br>
std::char_traits<char> > &)' lvalue Function 0x26d4480 'endl' <br>
'basic_ostream<char, struct std::char_traits<char> > &(basic_ostream<char, <br>
struct std::char_traits<char> > &)' (FunctionTemplate 0x26b9180 'endl')<br>
`-ReturnStmt 0x275f130 <line:14:3, col:10><br>
`-IntegerLiteral 0x275f110 <col:10> 'int' 0<br>
<br>
<br>
It seems useful to writing a matcher.<br>
<br>
I modified the removeCStrCalls tool with a debugging matcher, so that I can <br>
start broad, and incrementally narrow what I want to match, while printing <br>
out what I have actually matched:<br>
<br>
class Debugging : public ast_matchers::MatchFinder::MatchCallback {<br>
public:<br>
Debugging(tooling::Replacements *Replace)<br>
: Replace(Replace) {}<br>
<br>
virtual void run(const ast_matchers::MatchFinder::MatchResult &Result) {<br>
<br>
const Expr *Arg =<br>
Result.Nodes.getStmtAs<Expr>("match");<br>
std::string match = getText(*Result.SourceManager, *Arg);<br>
std::cout << "MATCH " << match << std::endl;<br>
<br>
}<br>
<br>
private:<br>
tooling::Replacements *Replace;<br>
};<br>
<br>
Is this the right/sane/only possible approach to the act of writing a <br>
matcher?<br>
<br>
>From the -ast-dump, it looks like I need to first match a <br>
CXXOperatorCallExpr, so I write this matcher:<br>
<br>
Finder.addMatcher(<br>
id("match", operatorCallExpr()),<br>
&Callback);<br>
<br>
which gives me lots of output, mostly from the iostream header. I need to <br>
get narrower.<br>
<br>
In the -ast-dump output there is a CXXMemberCallExpr nested in the <br>
CXXOperatorCallExpr. I make a logical jump at matching that:<br>
<br>
Finder.addMatcher(<br>
id("match", operatorCallExpr(memberCallExpr())),<br>
&Callback);<br>
<br>
However, that produces no output, so my logical jump must be incorrect.<br>
<br>
What is the correct logical jump here in order to narrow my match? <br>
<br>
How can I determine what logical jumps I can make, by looking at the ast-<br>
dump output? <br>
<br>
How does one go about *actually* writing matcher code? <br>
<br>
What is the understanding one must have, the logic one must have and the <br>
information one must have to hand (is ast-dump output useful or not)?<br>
<br>
To be clear (in case it is not already clear), I'm not looking for a <br>
finished solution for the match/replacement I'm trying to make. I'm asking <br>
what to spend time doing between opening my editor and running a tool that <br>
does what I need. How do I figure out what code I need to write?<br>
<br>
Note: I have read the docs. The section at<br>
<br>
<a href="http://clang.llvm.org/docs/LibASTMatchersTutorial.html#step-2-using-ast-matchers">http://clang.llvm.org/docs/LibASTMatchersTutorial.html#step-2-using-ast-matchers</a><br>
<br>
shows some incremental steps, but does not explain how they are chosen. <br>
<br>
How does one know to go from <br>
<br>
forStmt()<br>
<br>
to <br>
<br>
forStmt(hasLoopInit(declStmt(hasSingleDecl(varDecl()))))<br>
<br>
for example? That is the kind of information I am looking for.<br>
<br>
Thanks,<br>
<br>
Steve.<br>
<br>
<br>
<br>
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