aaron.ballman 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);
+ };
+}
----------------
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;
}
```
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D44602
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