lebedev.ri 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);
+ };
+}
----------------
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?
Repository:
rCTE Clang Tools Extra
https://reviews.llvm.org/D44602
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