[clang-tidy] modernize-avoid-c-arrays: avoid main function (PR40604)

[lebedev.ri]

Summary

The check should ignore the main function, the program entry point.
It is not possible to use std::array<> for the argv.
The alternative is to use char** argv.

Fixes PR40604

[JonasToth]

clang-tidy/modernize/AvoidCArraysCheck.cpp

35

There is FunctionDecl->castToDeclContext() which is probably a better fit here.

test/clang-tidy/modernize-avoid-c-arrays.cpp

90 ↗

(On Diff #185400)

main has a third optional argument for environment variables. Please add test case for that, too.
Could add a test for the char **argv-form to ensure these are not ignored somehow?

[lebedev.ri]

test/clang-tidy/modernize-avoid-c-arrays.cpp

90 ↗

(On Diff #185400)

char **argv form *is* ignored, that is why i have not seen this issue before.
It's not a C-Style array, but a pointer to a pointer to char.

[lebedev.ri]

clang-tidy/modernize/AvoidCArraysCheck.cpp

35

I'm guessing you meant cast*From*DeclContext().
Interesting, that function is never once used.
And it uses static_cast<>()..

[lebedev.ri]

Address review notes, adjust docs.

[lebedev.ri]

clang-tidy/modernize/AvoidCArraysCheck.cpp

35

I'm not too sure about this.
Given ParmVarDecl, are we sure it's DeclContext is *always* FunctionDecl?

[lebedev.ri]

Add an assert to ensure that clang::FunctionDecl::castFromDeclContext() is safe to do.

[JonasToth]

clang-tidy/modernize/AvoidCArraysCheck.cpp

35

From Doc "Represents a parameter to a function. " so i think it has always a FunctionDecl (or subclass) as DeclContext.

Maybe that function is a relict? I just saw it in the docs too and thought it makes sense to use it. No opinion on that, @aaron.ballman do you know more on that?

[aaron.ballman]

clang-tidy/modernize/AvoidCArraysCheck.cpp

35

From Doc "Represents a parameter to a function. " so i think it has always a FunctionDecl (or subclass) as DeclContext.

ObjCMethodDecl is not a subclass of FunctionDecl, yet it contains ParmVarDecl objects and is a DeclContext.

I would use dyn_cast here instead.

docs/clang-tidy/checks/modernize-avoid-c-arrays.rst

58

It's -> Its
params -> parameters

[lebedev.ri]

And back to dyn_cast().

[aaron.ballman]

LGTM aside from a nit.

clang-tidy/modernize/AvoidCArraysCheck.cpp

36–38

return FD ? FD->isMain() : false; ?

[lebedev.ri]

In D57787#1387406, @aaron.ballman wrote:

LGTM aside from a nit.

Thank you for the review.

clang-tidy/modernize/AvoidCArraysCheck.cpp

35

Aha!