[cfe-dev] [clang-tidy] Some possible contributions

Manuel Klimek via cfe-dev cfe-dev at lists.llvm.org
Mon Dec 14 02:16:15 PST 2015


On Sun, Dec 13, 2015 at 6:15 PM Piotr Dziwinski via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hello,
>
> I want to let you know that I'm still here and still working on clang-tidy
> checker for localizing variables.
> Sorry for the long delay, the time flies so fast.
>
> Anyway, I have some good and some bad news.
>
> The good news is that I got my checker to work correctly when it comes to
> handling nested scopes and control statements, including all the corner
> cases that I predicted.
> I even made provisions for things like introducing localized for loop
> counters and inserting braces where necessary in switch-case blocks.
>
> The bad news is that I ran into two issues that I couldn't resolve on my
> own, both of which are critical for the checker to be useful in real
> production code.
>
> Issue #1. Handling multiple variables declared in one declaration
> statement.
>
> The case of moving a single declaration is easy enough - I can just cut
> the whole declaration as written in program source and paste it somewhere
> else.
> But if I have to cut out only selected parts of a multiple declaration and
> move them, I need some way of parsing the declaration to separate parts of
> the statement.
> Let's take for example:
>
> long int a, *b, c[10];
>
> I want to obtain the necessary source locations from AST so that I can
> parse this declaration into four component strings:
>   - type identifier: "long int"
>   - first variable declaration: "a"
>   - second variable declaration: "*b"
>   - third variable declaration: "c[10]"
>
> Once I have that, it will be easy to independently cut out code between
> identified source locations and create insertions by putting together the
> strings from source code.
>
> I tried different methods of achieving that but given the interface of
> DeclStmt and Decl, I cannot find a way to do that reliably for all possible
> cases.
> I can obtain source locations for subsequent variable declarations, but
> these always point to beginning of variable name as it appears in code.
> What I need is actual source location separating "long int" from "a" and
> further locations of separating commas between declarations.
> Theoretically, I could use Lexer to find comma tokens, but there are also
> other contexts where comma may appear, such list of arguments of function
> pointer.
>
>
I believe you'll need to whip out the lexer for this currently.


> Issue #2. Merging multiple FixIt hint insertions in the same location.
>
> For example, given:
>
> int a; int b;
> // ...
> call(a, b); // first use of "a" and "b"
>
> My checker would generate two diagnostics:
>
>   - "variable "a" declaration can be moved closer to its point of use"
> with the following FixIt hint:
>
> int b;
> // ...
> int a; call(a, b);
>
>   - "variable "b" declaration can be moved closer to its point of use"
> with the following FixIt hint:
>
> int a;
> // ...
> int b; call(a, b);
>
> The end result of applying these FixIt hints is:
>
> // ...
> int b; call(a, b);
>
> So the removals are handled correctly, but in case of insertions, the
> second one overrides the first one. What I want is to have both insertions
> present, one after the other.
>
> So far, I have worked around this problem by clumping together such
> problematic FixIt hints to one of the diagnostics, so that they are applied
> all at once.
> However, this can be quite confusing for the user who would see seemingly
> unrelated FixIt hints under a diagnostic referring to only one variable.
> Needless to say, this also makes the code much more complicated than it
> needs to be as I have to store information first and emit diagnostics later.
>
> I don't know how to resolve this, as this is a more a problem with
> applying FixIt hints in general.
> Perhaps this is actually the intended behavior in some cases. Even so, I
> would like to have a way to address my use case, without impacting other
> use cases.
>
>
I think that has bitten us at some point, too - if this is still a problem,
I'd consider it a bug in clang-tidy's fixit handling.


>
>
> I would appreciate any pointers of how to tackle these two issues.
> I'm afraid that without solving them, my checker will remain in
> "always-beta" state.
>
> Meanwhile, if you are interested in current version of the code, you can
> check out my Github fork:
> https://github.com/piotrdz/clang-tools-extra
>
>
> Best regards,
> Piotr Dziwinski
>
>
> On 22/10/15 17:21, Richard via cfe-dev wrote:
>
> [Please reply *only* to the list and do not include my email directly
> in the To: or Cc: of your reply; otherwise I will not see your reply.
> Thanks.]
>
> In article <5626C26F.4040009 at gmail.com> <5626C26F.4040009 at gmail.com>,
>     Piotr Dziwinski via cfe-dev <cfe-dev at lists.llvm.org> <cfe-dev at lists.llvm.org> writes:
>
>
> It still needs work on corner cases and some hard cases like switch
> statements, which I've left out for now. And of course more tests. I
> will try to cover as much as possible in unit tests, but it's just
> impossible to test everything. The real verification will be running it
> on some production code. I will look at the project you gave as example,
> too.
>
> Areas where I have found refactoring tools to fail are with "exotic"
> types like pointer to function, pointer to member data and pointer to
> member function.  Sometimes things freak out with unions, too.
>
> I looked at your test file on github and it's already covering the
> idea of multiple variables declared in a single statement where one of
> them is localized later in the scope, so that looks good.
>
>
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