JonasToth added inline comments.
================
Comment at: test/clang-tidy/readability-function-size.cpp:207-212
+void variables_8() {
+ int a, b;
+ struct A {
+ A(int c, int d);
+ };
+}
----------------
lebedev.ri wrote:
> aaron.ballman wrote:
> > lebedev.ri wrote:
> > > aaron.ballman wrote:
> > > > JonasToth wrote:
> > > > > lebedev.ri wrote:
> > > > > > aaron.ballman wrote:
> > > > > > > lebedev.ri wrote:
> > > > > > > > aaron.ballman wrote:
> > > > > > > > > lebedev.ri wrote:
> > > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > > lebedev.ri wrote:
> > > > > > > > > > > > aaron.ballman wrote:
> > > > > > > > > > > > > I think the current behavior here is correct and the
> > > > > > > > > > > > > previous behavior was incorrect. However, it brings
> > > > > > > > > > > > > up an interesting question about what to do here:
> > > > > > > > > > > > > ```
> > > > > > > > > > > > > void f() {
> > > > > > > > > > > > > struct S {
> > > > > > > > > > > > > void bar() {
> > > > > > > > > > > > > int a, b;
> > > > > > > > > > > > > }
> > > > > > > > > > > > > };
> > > > > > > > > > > > > }
> > > > > > > > > > > > > ```
> > > > > > > > > > > > > Does `f()` contain zero variables or two? I would
> > > > > > > > > > > > > contend that it has no variables because S::bar() is
> > > > > > > > > > > > > a different scope than f(). But I can see a case
> > > > > > > > > > > > > being made about the complexity of f() being
> > > > > > > > > > > > > increased by the presence of the local class
> > > > > > > > > > > > > definition. Perhaps this is a different facet of the
> > > > > > > > > > > > > test about number of types?
> > > > > > > > > > > > As previously briefly discussed in IRC, i **strongly**
> > > > > > > > > > > > believe that the current behavior is correct, and
> > > > > > > > > > > > `readability-function-size`
> > > > > > > > > > > > should analyze/diagnose the function as a whole,
> > > > > > > > > > > > including all sub-classes/sub-functions.
> > > > > > > > > > > Do you know of any coding standards related to this check
> > > > > > > > > > > that weigh in on this?
> > > > > > > > > > >
> > > > > > > > > > > What do you think about this:
> > > > > > > > > > > ```
> > > > > > > > > > > #define SWAP(x, y) ({__typeof__(x) temp = x; x = y; y =
> > > > > > > > > > > x;})
> > > > > > > > > > >
> > > > > > > > > > > void f() {
> > > > > > > > > > > int a = 10, b = 12;
> > > > > > > > > > > SWAP(a, b);
> > > > > > > > > > > }
> > > > > > > > > > > ```
> > > > > > > > > > > Does f() have two variables or three? Should presence of
> > > > > > > > > > > the `SWAP` macro cause this code to be more complex due
> > > > > > > > > > > to having too many variables?
> > > > > > > > > > Datapoint: the doc
> > > > > > > > > > (`docs/clang-tidy/checks/readability-function-size.rst`)
> > > > > > > > > > actually already states that macros *are* counted.
> > > > > > > > > >
> > > > > > > > > > ```
> > > > > > > > > > .. option:: StatementThreshold
> > > > > > > > > >
> > > > > > > > > > Flag functions exceeding this number of statements. This
> > > > > > > > > > may differ
> > > > > > > > > > significantly from the number of lines for macro-heavy
> > > > > > > > > > code. The default is
> > > > > > > > > > `800`.
> > > > > > > > > > ```
> > > > > > > > > > ```
> > > > > > > > > > .. option:: NestingThreshold
> > > > > > > > > >
> > > > > > > > > > Flag compound statements which create next nesting
> > > > > > > > > > level after
> > > > > > > > > > `NestingThreshold`. This may differ significantly from
> > > > > > > > > > the expected value
> > > > > > > > > > for macro-heavy code. The default is `-1` (ignore the
> > > > > > > > > > nesting level).
> > > > > > > > > > ```
> > > > > > > > > My concerns relate to what's considered a "variable declared
> > > > > > > > > in the body" (per the documentation) in relation to function
> > > > > > > > > complexity. To me, if the variable is not accessible
> > > > > > > > > lexically within the body of the function, it's not adding to
> > > > > > > > > the function's complexity *for local variables*. It may
> > > > > > > > > certainly be adding other complexity, of course.
> > > > > > > > >
> > > > > > > > > I would have a very hard time explaining to a user that
> > > > > > > > > variables they cannot see or change (assuming the macro is in
> > > > > > > > > a header file out of their control) contribute to their
> > > > > > > > > function's complexity. Similarly, I would have difficulty
> > > > > > > > > explaining that variables in an locally declared class member
> > > > > > > > > function contribute to the number of variables in the outer
> > > > > > > > > function body, but the class data members somehow do not.
> > > > > > > > >
> > > > > > > > > (per the documentation)
> > > > > > > >
> > > > > > > > Please note that the word `complexity` is not used in the
> > > > > > > > **documentation**, only `size` is.
> > > > > > > >
> > > > > > > > There also is the other side of the coin:
> > > > > > > >
> > > > > > > > ```
> > > > > > > > #define simple_macro_please_ignore \
> > > > > > > > the; \
> > > > > > > > actual; \
> > > > > > > > content; \
> > > > > > > > of; \
> > > > > > > > the; \
> > > > > > > > foo();
> > > > > > > >
> > > > > > > > // Very simple function, nothing to see.
> > > > > > > > void foo() {
> > > > > > > > simple_macro_please_ignore();
> > > > > > > > }
> > > > > > > >
> > > > > > > > #undef simple_macro_please_ignore
> > > > > > > > ```
> > > > > > > >
> > > > > > > > In other words, if we ignore macros, it would be possible to
> > > > > > > > abuse them to artificially reduce complexity, by hiding it in
> > > > > > > > the macros.
> > > > > > > > I agree that it's total abuse of macros, but macros are in
> > > > > > > > general not nice, and it would not be good to give such things
> > > > > > > > a pass.
> > > > > > > >
> > > > > > > >
> > > > > > > > > My concerns relate to what's considered a "variable declared
> > > > > > > > > in the body" (per the documentation) in relation to function
> > > > > > > > > complexity.
> > > > > > > >
> > > > > > > > Could you please clarify, at this point, your concerns are only
> > > > > > > > about this new part of the check (variables), or for the entire
> > > > > > > > check?
> > > > > > > > In other words, if we ignore macros, it would be possible to
> > > > > > > > abuse them to artificially reduce complexity, by hiding it in
> > > > > > > > the macros.
> > > > > > >
> > > > > > > I don't disagree, that's why I'm trying to explore the
> > > > > > > boundaries. Your example does artificially reduce complexity. My
> > > > > > > example using swap does not -- it's an idiomatic swap macro where
> > > > > > > the inner variable declaration adds no complexity to the calling
> > > > > > > function as it's not exposed to the calling function.
> > > > > > >
> > > > > > > > Could you please clarify, at this point, your concerns are only
> > > > > > > > about this new part of the check (variables), or for the entire
> > > > > > > > check?
> > > > > > >
> > > > > > > Only the new part of the check involving variables.
> > > > > > > > Could you please clarify, at this point, your concerns are only
> > > > > > > > about this new part of the check (variables), or for the entire
> > > > > > > > check?
> > > > > >
> > > > > > > Only the new part of the check involving variables.
> > > > > >
> > > > > > OK.
> > > > > >
> > > > > > This should be split into two boundaries:
> > > > > > * macros
> > > > > > * the nested functions/classes/methods in classes.
> > > > > >
> > > > > > I *think* it may make sense to give the latter a pass, no strong
> > > > > > opinion here.
> > > > > > But not macros.
> > > > > > (Also, i think it would be good to treat macros consistently within
> > > > > > the check.)
> > > > > >
> > > > > > Does anyone else has an opinion on how that should be handled?
> > > > > what is the current behaviour for aarons nested function?
> > > > > i checked cppcoreguidelines and hicpp and they did not mention such a
> > > > > case and i do not recall any rule that might relate to it.
> > > > >
> > > > > I think aaron has a good point with:
> > > > > > I would have a very hard time explaining to a user that variables
> > > > > > they cannot see or change (assuming the macro is in a header file
> > > > > > out of their control) contribute to their function's complexity.
> > > > > > Similarly, I would have difficulty explaining that variables in an
> > > > > > locally declared class member function contribute to the number of
> > > > > > variables in the outer function body, but the class data members
> > > > > > somehow do not.
> > > > >
> > > > > But I see no way to distinguish between "good" and "bad" macros, so
> > > > > macro expansions should add to the variable count, even though your
> > > > > swap macro is a valid counter example.
> > > > > But I see no way to distinguish between "good" and "bad" macros, so
> > > > > macro expansions should add to the variable count, even though your
> > > > > swap macro is a valid counter example.
> > > >
> > > > I would constrain it this way: variables declared in local class member
> > > > function definitions and expression statements within a macro expansion
> > > > do not contribute to the variable count, all other local variables do.
> > > > e.g.,
> > > > ```
> > > > #define SWAP(x, y) ({__typeof__(x) temp = x; x = y; y = x;})
> > > >
> > > > void two_variables() {
> > > > int a = 10, b = 12;
> > > > SWAP(a, b);
> > > > }
> > > >
> > > > void three_variables() {
> > > > int a = 10, b = 12;
> > > > ({__typeof__(x) temp = x; x = y; y = x;})
> > > > }
> > > >
> > > > void one_variable() {
> > > > int i = 12;
> > > > class C {
> > > > void four_variables() {
> > > > int a, b, c, d;
> > > > }
> > > > };
> > > > }
> > > >
> > > > #define FOO(x) (x + ({int i = 12; i;}))
> > > >
> > > > void five_variables() {
> > > > int a, b, c, d = FOO(100);
> > > > float f;
> > > > }
> > > > ```
> > > > I would constrain it this way: variables declared in local class member
> > > > function definitions and expression statements within a macro expansion
> > > > do not contribute to the variable count, all other local variables do.
> > >
> > > But we do already count statements, branches and compound statements in
> > > all those cases in this check.
> > > Why should variables be an exception?
> > > But we do already count statements, branches and compound statements in
> > > all those cases in this check.
> > Why should variables be an exception?
> >
> > Why should variables that are entirely inaccessible to the function count
> > towards the function's variable complexity?
> >
> > Things like macros count towards a function's line count because the macros
> > are expanded into the function. I don't agree with this choice, but I can
> > at least explain it to someone I'm teaching. In the case of variable
> > declarations, I have no justification for those variables adding complexity
> > because they cannot be named within the function even though the macro is
> > expanded in the function. Yet the check doesn't count global variables
> > which do add to function complexity when used within the function.
> >
> > For those design reasons, I'd also be opposed to diagnosing this (assume it
> > requires 2 variables to trigger the diagnostic):
> > ```
> > void one_variable() {
> > auto lambda = []() { int a = 12, b = 100; return a + b; };
> > }
> > ```
> > which is functionally equivalent to:
> > ```
> > void one_variable() {
> > struct S {
> > int operator()() { int a = 12, b = 100; return a + b; }
> > } lambda;
> > }
> > ```
> Ok, done. But this raises another question:
> ```
> #define vardecl(type, name) type name;
> void variables_15() {
> // FIXME: surely we should still warn here?
> vardecl(int, a);
> vardecl(int, b);
> }
> ```
> I'm guessing we want to still warn in cases like this?
how would you differentiate? I am against trying to get all macro cases right,
either warn for everything in macros or nothing.
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D44602
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