[cfe-dev] Proposal: add "replace" functionality to clang-query

[Alexander Timin via cfe-dev]

Thanks Yitzhak and Aaron!

As an outsider to the clang land, I wasn't aware of the Transformer —
thanks for pointing me to it, it looks really exciting.

I think that my proposal can be broken down into two parts:
a) Adding an option to generate replacements without having to build a C++
tool.
b) Particular syntax to generate these replacements.

I think that Transformer effort covers only the b) part — please correct me
if I'm wrong.

And out of these two, I (looking at the things from the user perspective)
think that a) is the most important one, as having to write
and link C++ code adds a lot of friction to the process (so sed + manual
edits are still faster). So I think that there is a nice synergy
potential in the long term — I think that the ideal end state would be
having the ability to write Transformer-based queries dynamically in
clang-query, something like that:

$ clang-query
> transform matcher makeStencil(ifBound("value", true, false))

However (as building the dynamic Stencils sounds non-trivial), I think that
there is no particular harm in having both options available in
clang-query, one being easier to write and one being more flexible:

> replace matcher foo = ${foo}
> transform matcher complexStencil(...)


On Wed, 25 Mar 2020 at 17:05, Yitzhak Mandelbaum <yitzhakm at google.com>
wrote:

> Aaron, thanks for mentioning Clang Transformer. Alexander, you can find
> the original doc here
> <https://docs.google.com/document/d/1ppw0RhjwsrbBcHYhI85pe6ISDbA6r5d00ot3N8cQWeQ/edit#heading=h.qjjywl5dhpsb>.
> The code is under Tooling:
> https://github.com/llvm/llvm-project/tree/master/clang/include/clang/Tooling/Transformer
>
> On Wed, Mar 25, 2020 at 12:52 PM Aaron Ballman <aaron at aaronballman.com>
> wrote:
>
>> On Tue, Mar 24, 2020 at 4:22 PM Alexander Timin via cfe-dev
>> <cfe-dev at lists.llvm.org> wrote:
>> >
>> > Hey!
>> >
>> > I think that medium-scale medium-complexity C++ refactorings (like
>> replacing the order of the two arguments of a function across a large
>> codebase) are much harder that they should be: clang-refactor and
>> clang-rename do not cover them and writing a full libTooling tool is not
>> the most time-efficient solution.
>> >
>> > I propose extending the functionality of clang-query to cover this use
>> case and allow generating replacements (which can be then applied by
>> clang-apply-replacements) from matches:
>> >
>> > replace MATCHER NODE PATTERN
>> >
>> > for example,
>> >
>> > let f = cxxMethodDecl(hasName("Foo"))
>> > let arg1 = hasArgument(0, expr().bind("arg1"))
>> > let arg2 = hasArgument(1, expr().bind("arg2"))
>> > let m = callExpr(on(f), arg1, arg2)
>> > replace m root Foo(${arg2}, ${arg1})
>> >
>> > A more detailed design doc is available here.
>> >
>> > An early prototype patch is available here.
>> > A real-life example: the query is here, the output in the form of a
>> Chromium patch is here.
>> >
>> > WDYT?
>>
>> Thank you for bringing up this idea, I've wanted something that can do
>> this for a while. I think the idea has a lot of merit, but I'm
>> wondering whether we want to focus on code transformations within
>> clang-query like this as opposed to putting that effort into the
>> in-progress Transformer work
>> (http://lists.llvm.org/pipermail/cfe-dev/2019-January/060950.html).
>> Are you aware of those efforts? If so, how do you see this proposal
>> coexisting with that functionality?
>>
>> ~Aaron
>>
>>
>> > Alexander
>> > _______________________________________________
>> > cfe-dev mailing list
>> > cfe-dev at lists.llvm.org
>> > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>
>
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