[cfe-dev] [PATCH] LibTooling docs

Fri Apr 20 09:36:57 PDT 2012

I re-read Chris' tutorials, and they are all active. So ignore that. :-) All your changes look fine! 

Off the record: I am also a non-native English speaker (as I assume you are, correct me if I am wrong), but I learned that apparently "basically" is abused so much that some people will question if you really know what you are talking about :-/ And unfortunately, in my experience, I am afraid they are right. I do not doubt you knowledge, but it is something I had to learn "the hard way".

-- Erik

On 20 apr. 2012, at 10:30, Manuel Klimek <klimek at google.com> wrote:

> On Thu, Apr 19, 2012 at 5:42 PM, Erik Verbruggen <erikjv at me.com> wrote:
>> 
>> On Apr 19, 2012, at 16:36, Manuel Klimek wrote:
>> 
>>> Please find a first version attached.
>>> 
>>> The next step is a short intro on how to write a FrontendAction, which
>>> is common to clang plugins and libtooling, and thus I thought I'd put
>>> it into a separate doc.
>> 
>> 
>> Comments inline
>> 
>> Cheers,
>> Erik.
>> 
>> 
>>> LibTooling
>>> 
>>> LibTooling is a library to support writing standalone tools based on Clang. This document will provide a basic walkthrough of how to write a tool using LibTooling.
>>> 
>>> Introduction
>>> 
>>> Tools built with LibTooling, like Clang Plugins, run FrontendActions over code. In this tutorial, we'll demonstrate the different ways of
>> 
>> Don't use "we". "This tutorial demonstrates ..." is better. Same for constructs like "we'll": in colloquial communication that is okay, but otherwise you should use "we will". The only kind-of-exception is "don't" or any use of "n't" for "not".
> 
> I disagree with the idea that we need to be overly formal in those
> tutorials. Now, if you think that some of my bad grammar makes the
> sentences hard to understand / read, I'm happy to change, but I don't
> think that a style that's more dry makes it easier to read...
> 
>>> running clang's SyntaxOnlyAction, which basically runs a quick syntax check, over a bunch of code.
>> 
>> Try not to use "basically", as it might sound like you just don't know what really happens. Now in all honesty, I have no better way of phrasing this sentence...
> 
> Done (just removed the "basically" :)
> 
>>> Parsing a code snippet in memory...
>> 
>> Ellipsis? Why not a dot/full-stop like in other headers?
> 
> Done.
> 
>>> If you ever wanted to run a FrontendAction over some sample code, for example to unit test parts of the Clang AST, runToolOnCode is what you looked for. Let me give you an example:
>>> 
>>>   #include "clang/Tooling/Tooling.h"
>>> 
>>>   TEST(runToolOnCode, CanSyntaxCheckCode) {
>>>     // runToolOnCode returns whether the action was correctly run over the
>>>     // given code.
>>>     EXPECT_TRUE(runToolOnCode(new clang::SyntaxOnlyAction, "class X {};"));
>>>   }
>>> 
>>> Writing a standalone tool.
>>> 
>>> Once you unit tested your FrontendAction to the point where it cannot possibly break, it's time to create a standalone tool. For a
>> 
>> "it is"
>> 
>>> standalone tool to run clang, it first needs to figure out what command line arguments it needs for a specified file. To that end we want to create a CompilationDatabase.
>> 
>> ".. we want to ..." could be read as one-of-the-ways-to-do-it. Is it? Otherwise just state: "To that end a CompilationDatabase is needed."
> 
> I try to avoid passive voice wherever possible. Changed to "To that
> end we create a CompilationDatabase."
> 
>>> Creating a compilation database.
>>> 
>>> CompilationDatabase provides static factory functions to help with parsing compile commands from a build directory or the command line. To allow both explicit specification of a compile command line, as well as retrieving the compile command lines from a database, we can write:
>> 
>> "To allow....can write:" -> "The following code allows for both explicit specification of a compile command line, as well as retrieving the compile commands lines from a database."
> 
> Done.
> 
>>> int main(int argc, const char **argv) {
>>>   // First, try to create a fixed compile command database from the command line
>>>   // arguments.
>>>   llvm::OwningPtr<CompilationDatabase> Compilations(
>>>     FixedCompilationDatabase::loadFromCommandLine(argc, argv));
>>> 
>>>   // Next, use normal llvm command line parsing to get the tool specific
>>>   // parameters.
>>>   cl::ParseCommandLineOptions(argc, argv);
>>> 
>>>   if (!Compilations) {
>>>     // In case the user did not specify the compile command line via positional
>>>     // command line arguments after "--", try to load the compile commands from
>>>     // a database in the specified build directory.
>>>     std::string ErrorMessage;
>>>     Compilations.reset(CompilationDatabase::loadFromDirectory(BuildPath,
>>>                                                               ErrorMessage));
>>> 
>>>     // If there is still no valid compile command database, we don't know how
>>>     // to run the tool.
>>>     if (!Compilations)
>>>       llvm::report_fatal_error(ErrorMessage);
>>>   }
>>> ...
>>> }
>>> 
>>> Creating and running a ClangTool.
>>> 
>>> One we have a CompilationDatabase, we can create a ClangTool and run our FrontendAction over some code. For example, to run the
>> 
>> OnCe (note the C :-) ). But better: "Once the CompilationDatabase is created, ...."
> 
> Again, my strong preference for active voice trumps the idea of more formality.
> 
>>> SyntaxOnlyAction over the files "a.cc" and "b.cc" one would write:
>> 
>> "... one would write:" -> "the following code-snippet can be used:"
>> 
>>>   // A clang tool can run over a number of sources in the same process...
>>>   std::vector<std::string> Sources;
>>>   Sources.push_back("a.cc");
>>>   Sources.push_back("b.cc");
>>> 
>>>   // We hand the CompilationDatabase we created and the sources to run over into
>>>   // the tool constructor.
>>>   ClangTool Tool(*Compilations, Sources);
>>> 
>>>   // The ClangTool needs a new FrontendAction for each translation unit we run
>>>   // on. Thus, it takes a FrontendActionFactory as parameter. To create a
>>>   // FrontendActionFactory from a given FrontendAction type, we call
>>>   // newFrontendActionFactory<clang::SyntaxOnlyAction>().
>>>   int result = Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>());
>>> 
>>> Putting it together - the first tool.
>>> 
>>> Now we combine the two previous steps into our first real tool. This example tool is also checked into the clang tree at tools/clang-check/ClangCheck.cpp.
>> 
>> "To combine the two..."
> 
> Not sure where this would go?
> 
>>>   #include "llvm/Support/CommandLine.h"
>>>   #include "clang/Frontend/FrontendActions.h"
>>>   #include "clang/Tooling/CompilationDatabase.h"
>>>   #include "clang/Tooling/Tooling.h"
>>> 
>>>   using namespace clang::tooling;
>>>   using namespace llvm;
>>> 
>>>   cl::opt<std::string> BuildPath(
>>>     cl::Positional,
>>>     cl::desc("<build-path>"));
>>> 
>>>   cl::list<std::string> SourcePaths(
>>>     cl::Positional,
>>>     cl::desc("<source0> [... <sourceN>]"),
>>>     cl::OneOrMore);
>>> 
>>>   int main(int argc, const char **argv) {
>>>     llvm::OwningPtr<CompilationDatabase> Compilations(
>>>       FixedCompilationDatabase::loadFromCommandLine(argc, argv));
>>>     cl::ParseCommandLineOptions(argc, argv);
>>>     if (!Compilations) {
>>>       std::string ErrorMessage;
>>>       Compilations.reset(CompilationDatabase::loadFromDirectory(BuildPath,
>>>                                                                 ErrorMessage));
>>>       if (!Compilations)
>>>         llvm::report_fatal_error(ErrorMessage);
>>>     }
>>>     ClangTool Tool(*Compilations, SourcePaths);
>>>     return Tool.run(newFrontendActionFactory<clang::SyntaxOnlyAction>());
>>>   }
>>> 
>>> Running the tool on some code.
>>> 
>>> When you check out and build clang, clang-check is already built and available to you in bin/clang-check inside your build directory.
>>> 
>>> You can run try clang-check on a file in the llvm repository by specifying all the needed parameters after a "--" separator:
>>> 
>>>   $ cd /path/to/source/llvm
>>>   $ export BD=/path/to/build/llvm
>>>   $ $BD/bin/clang-check . tools/clang/tools/clang-check/ClangCheck.cpp -- \
>>>     clang++ -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS \
>>>     -Itools/clang/include -I$BD/include -Iinclude -Itools/clang/lib/Headers -c
>>> 
>>> As an alternative, you can also configure cmake to output a compile command database into its build directory:
>>> 
>>>   # Alternatively to calling cmake, use ccmake, toggle to advanced mode and
>>>   # set the parameter CMAKE_EXPORT_COMPILE_COMMANDS from the UI.
>>>   $ cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON .
>>> 
>>> This creates a file called compile_commands.json in the build directory. Now you can run clang-check over files in the project by specifying the build path as first argument and some source files as further positional arguments:
>>> 
>>>   $ cd /path/to/source/llvm
>>>   $ export BD=/path/to/build/llvm
>>>   $ $BD/bin/clang-check $BD tools/clang/tools/clang-check/ClangCheck.cpp
> 
> Thanks for the review!
> 
> /Manuel
> <LibTooling.html>