[clang-tidy] readability-function-size: add VariableThreshold param.

[lebedev.ri]

Summary

Pretty straight-forward, just count all the variable declarations in the function's body, and if more than the configured threshold - do complain.

Note that this continues perverse practice of disabling the new option by default.
I'm not certain where is the balance point between not being too noisy, and actually enforcing the good practice.
If we really want to not disable this by default, but also to not cause too many new warnings, we could default to 50 or so.
But that is a lot of variables too...

I was able to find one coding style referencing variable count:

• https://www.kernel.org/doc/html/v4.15/process/coding-style.html#functions
  
  > Another measure of the function is the number of local variables. They shouldn’t exceed 5-10, or you’re doing something wrong.

[Eugene.Zelenko]

docs/ReleaseNotes.rst

154

Will be good idea to add option to clarify improvement.

[lebedev.ri]

Adjusted ReleaseNotes change.

[JonasToth]

docs/ReleaseNotes.rst

157

I would rephrase this a little to:

Flags function bodies exceeding this number of declared variables.

test/clang-tidy/readability-function-size.cpp

118

Why is this check here and not on line 100 like the other conditions?

144

same here.

153

Could you please add a test for function having more parameters then allowed variables, but no variables?

180

This testfile is not C++17 right now, but do you know how structured bindings are handled? Maybe its worth adding another file for C++17 testing it.

Could you add a little test for range based for loops?

[lebedev.ri]

Address jonastoth's review notes.

• Properly support C++17 structured bindings.
• A few more tests

[JonasToth]

Looks fine to me, but Aaron or someone else must accept :)

Just out of curiosity: The decomposition visit is for structured binding and the binding visit for range based for? Are there other places where binding occurs, for example in some template stuff?
Just asking if this might hit me in a other check :D

[lebedev.ri]

In D44602#1041153, @JonasToth wrote:

Looks fine to me, but Aaron or someone else must accept :)

Thanks for review!

In D44602#1041153, @JonasToth wrote:

Just out of curiosity: The decomposition visit is for structured binding and the binding visit for range based for? Are there other places where binding occurs, for example in some template stuff?
Just asking if this might hit me in a other check :D

The comment i added is actually wrong.
The range-based for just works anyway.
The VisitBindingDecl() is needed to get all the 'variables' declared in structured binding.
But as you can see in https://godbolt.org/g/be6Juf, the BindingDecl's are wrapped into DecompositionDecl.
And DecompositionDecl is actually inherited from VarDecl, https://github.com/llvm-mirror/clang/blob/b031fdc9b7dbd9c7f942d8060a4f00d63f3c9af2/include/clang/AST/DeclCXX.h#L3824-L3825,
so we count the DecompositionDecl in VisitVarDecl(), thus we need a VisitDecompositionDecl() that subtracts it.

This may be the wrong/incomplete solution.

docs/ReleaseNotes.rst

157

I agree that it looks gibberish. Reworded a little. Probably still not ideal.

test/clang-tidy/readability-function-size.cpp

118

It can not be there, the note: nesting level <> starts here (threshold 2) are outputted before note: <> variables (threshold 1), and filecheck respects the order of // CHECK-MESSAGES:

153

It's already checked in foo7(), but sure.

180

This testfile is not C++17 right now, but do you know how structured bindings are handled? Maybe its worth adding another file for C++17 testing it.

Nice catch!

Could you add a little test for range based for loops?

Added. I expected them to not work (after a quick look at AST), but apparently they just work..

[JonasToth]

The comment i added is actually wrong.
The range-based for just works anyway.
The VisitBindingDecl() is needed to get all the 'variables' declared in structured binding.
But as you can see in https://godbolt.org/g/be6Juf, the BindingDecl's are wrapped into DecompositionDecl.
And DecompositionDecl is actually inherited from VarDecl, https://github.com/llvm-mirror/clang/blob/b031fdc9b7dbd9c7f942d8060a4f00d63f3c9af2/include/clang/AST/DeclCXX.h#L3824-L3825,
so we count the DecompositionDecl in VisitVarDecl(), thus we need a VisitDecompositionDecl() that subtracts it.

Thanks for clarification. It feels very NOT obvious how to handle this case :)

[JonasToth]

docs/ReleaseNotes.rst

157

Its better. But the native speakers should give a final thought.

test/clang-tidy/readability-function-size.cpp

118

I see, no problems then :)

180

Added. I expected them to not work (after a quick look at AST), but apparently they just work..

Life would be so much easier if this is always the case :D

[aaron.ballman]

clang-tidy/readability/FunctionSizeCheck.cpp

30–31

This comment could be clarified. I think what it's trying to express is that the decomposition declaration was already counted as a variable declaration but we do not want to count it as such.

I think a better way to express this is to change VisitVarDecl() to check isa<DecompositionDecl>() and not increment in that case, rather than increment in one place and decrement in another. You could also check isa<ParmVarDecl>() at the same time and skip subtracting off formal parameters.

docs/ReleaseNotes.rst

157

I'd tweak slightly: Flags functions that have more than a specified number of variables declared in the body.

docs/clang-tidy/checks/readability-function-size.rst

42

This should clarify that parameters do not count as variables declared in the body.

[lebedev.ri]

Address @aaron.ballman's review notes.

I'm not sure the change re ParmVarDecl handling is actually correct, see testcase.

clang-tidy/readability/FunctionSizeCheck.cpp

30–31

This comment could be clarified. I think what it's trying to express is that the decomposition declaration was already counted as a variable declaration but we do not want to count it as such.

Yep.

I think a better way to express this is to change VisitVarDecl() to check isa<DecompositionDecl>() and not increment in that case, rather than increment in one place and decrement in another.

I agree.

You could also check isa<ParmVarDecl>() at the same time and skip subtracting off formal parameters.

That is a behavior-changing change, actually.
But i don't have any strong preferences here, so changed, test added.

docs/clang-tidy/checks/readability-function-size.rst

42

This gets oh so more interesting with the testcase i added.
I'm not sure whether we actually want to ignore all the ParmVarDecl, or keep

unsigned ActualNumberParameters = Func->getNumParams();
unsigned BodyVariables = FI.Variables - ActualNumberParameters;

[aaron.ballman]

test/clang-tidy/readability-function-size.cpp

207–212

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?

[lebedev.ri]

test/clang-tidy/readability-function-size.cpp

207–212

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.

[aaron.ballman]

test/clang-tidy/readability-function-size.cpp

207–212

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?

[lebedev.ri]

test/clang-tidy/readability-function-size.cpp

207–212

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).

[aaron.ballman]

test/clang-tidy/readability-function-size.cpp

207–212

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.

[lebedev.ri]

test/clang-tidy/readability-function-size.cpp

207–212

(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?

[aaron.ballman]

test/clang-tidy/readability-function-size.cpp

207–212

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.

[lebedev.ri]

test/clang-tidy/readability-function-size.cpp

207–212

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?

[JonasToth]

test/clang-tidy/readability-function-size.cpp

207–212

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.

[aaron.ballman]

test/clang-tidy/readability-function-size.cpp

207–212

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;
}

[lebedev.ri]

test/clang-tidy/readability-function-size.cpp

207–212

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?

[aaron.ballman]

test/clang-tidy/readability-function-size.cpp

207–212

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;
}

[Eugene.Zelenko]

docs/ReleaseNotes.rst

154

Please rebase from trunk and use :doc: for link.

[kimgr]

I have to say I disagree that either the nested struct/function or macros
(in any form) should count toward a function's total variable count.

Both are valid forms of abstraction, and they both remove complexity from
the containing function since they factor details *out of the function's
immediate lexical contents* (I avoid 'scope' as macros do pollute the
scope) in a way that improves readability.

There are cases where macros can make things more complex but it seems
unfair to flag variables declared by macros as making expanding functions
more complex.

In short, I think I agree with Aaron's last example classifications.

• Kim

Den tors 22 mars 2018 14:56Eugene Zelenko via Phabricator via cfe-commits <
[e-mail]> skrev:

Eugene.Zelenko added inline comments.

Comment at: docs/ReleaseNotes.rst:127

+- Added VariableThreshold option to `readability-function-size
+ <
http://clang.llvm.org/extra/clang-tidy/checks/readability-function-size.html>`_

check

Please rebase from trunk and use :doc: for link.

Repository:

rCTE Clang Tools Extra

https://reviews.llvm.org/D44602

---

cfe-commits mailing list
[e-mail]
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits

[lebedev.ri]

Ok then :)
Let's only count the variables in the function itself, not in macros/nested functions/nested lambdas/nested classes/...

[lebedev.ri]

• Rebased ontop of master
• Fixed links in documentation
• Improved test coverage
• No longer count variables declared in nested classes.
• No longer count variables declared in nested lambdas. FIXME: this check()` is not being called for lambdas at all. But out of the scope of this patch.
• No longer count variables declared in macro expansion. Please see FIXME, i think this is too broad.

test/clang-tidy/readability-function-size.cpp

207–212

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?

[JonasToth]

test/clang-tidy/readability-function-size.cpp

207–212

how would you differentiate? I am against trying to get all macro cases right, either warn for everything in macros or nothing.

[lebedev.ri]

In D44602#1047574, @lebedev.ri wrote:

• No longer count variables declared in macro expansion. Please see FIXME, i think this is too broad.

Ping, thoughts?

[lebedev.ri]

Ping.

@aaron.ballman ping, do you have any further thoughts on that macro false-negative?

#define vardecl(type, name) type name;
void variables_15() {
  // FIXME: surely we should still warn here?
  vardecl(int, a);
  vardecl(int, b);
}
// CHECK-MESSAGES: :[[@LINE-5]]:6: warning: function 'variables_15' exceeds recommended size/complexity thresholds [readability-function-size]
// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 4 lines including whitespace and comments (threshold 0)

[aaron.ballman]

clang-tidy/readability/FunctionSizeCheck.cpp

31

This isn't the restriction I was envisioning. I was thinking more along the lines of:

bool VisitStmtExpr(StmtExpr *SE) override {
  ++StructNesting;
  Base::VisitStmtExpr(SE);
  --StructNesting;
  return true;
}

Basically -- treat a statement expression the same as an inner struct or lambda because the variables declared within it are scoped *only* to the statement expression.

You could argue that we should also add: if (!SE->getLocation.isMacroID()) { Base::VisitStmtExpr(SE); } to the top of the function so that you only treat statement expressions that are themselves in a macro expansion get this special treatment. e.g.,

void one_var() {
  (void)({int a = 12; a;});
}

#define M ({int a = 12; a;})
void zero_var() {
  (void)M;
}

I don't have strong opinions on this, but weakly lean towards treating all statement expressions the same way.

docs/clang-tidy/checks/readability-function-size.rst

44–46

I'd combine these into a serial list, like: Please note that function parameters and variables declared in macro expansions, lambdas, and nested class inline functions are not counted.

test/clang-tidy/readability-function-size.cpp

207–212

I'm guessing we want to still warn in cases like this?

That would be nice, yes. That's why the cut-point I was recommending were situations where the declared variables are not accessible within the function.

[lebedev.ri]

• Update
• Ignore GNU Statement Expressions too.
• Slightly reword docs.

clang-tidy/readability/FunctionSizeCheck.cpp

31

Ah, i did not really knew about GNU Statement Expression, so i did not ignore them.
Test added, and ignored.

test/clang-tidy/readability-function-size.cpp

207–212

Ok. Any hint on how to actually do that?
I guess i could look at DeclRefExpr, but that would only count those macro variables,
that are actually used, while the check is trying not to differentiate.

[lebedev.ri]

After a quick IRC chat with @aaron.ballman, it was discovered that there has been a big misunderstanding:

we don't need to ignore/exempt *all* the variables declared in macros, we just need to ignore *all* GNU Statement Expressions.

Yay!

I think this is ready now, please review.

[aaron.ballman]

Aside from some minor nits, LGTM!

clang-tidy/readability/FunctionSizeCheck.cpp

28

Comment is now stale.

31

Do you mind switching these to preincrement (and predecrement, below) since the value is not subsequently used?

[lebedev.ri]

• Drop stale comment
• Switch to pre{in,de}crement

[lebedev.ri]

@alexfh i'm waiting for some comment from you. there was no comment added when you removed yourself as a reviewer,
so i *assume* the usual message of that time was meant - "removing from my review queue, re-add when others have accepted.".

[alexfh]

In D44602#1065331, @lebedev.ri wrote:

@alexfh i'm waiting for some comment from you. there was no comment added when you removed yourself as a reviewer,
so i *assume* the usual message of that time was meant - "removing from my review queue, re-add when others have accepted.".

No, I just think that other reviewers can handle this. Feel free to commit as long as there are no open concerns.

[lebedev.ri]

In D44602#1065366, @alexfh wrote:

In D44602#1065331, @lebedev.ri wrote:

@alexfh i'm waiting for some comment from you. there was no comment added when you removed yourself as a reviewer,
so i *assume* the usual message of that time was meant - "removing from my review queue, re-add when others have accepted.".

No, I just think that other reviewers can handle this. Feel free to commit as long as there are no open concerns.

Ah, ok, i'll commit it then, thanks!

clang-tidy/readability/FunctionSizeCheck.h

 ///   * `BranchThreshold` - flag functions exceeding this number of control
 ///     statements. The default is `-1` (ignore the number of branches).
 ///   * `ParameterThreshold` - flag functions having a high number of
 ///     parameters. The default is `-1` (ignore the number of parameters).
 ///   * `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).
+///   * `VariableThreshold` - flag functions having a high number of variable
+///     declarations. The default is `-1` (ignore the number of variables).
 class FunctionSizeCheck : public ClangTidyCheck {
 public:
   FunctionSizeCheck(StringRef Name, ClangTidyContext *Context);
 
   void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
 
 private:
   const unsigned LineThreshold;
   const unsigned StatementThreshold;
   const unsigned BranchThreshold;
   const unsigned ParameterThreshold;
   const unsigned NestingThreshold;
+  const unsigned VariableThreshold;
 };
 
 } // namespace readability
 } // namespace tidy
 } // namespace clang
 
 #endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_FUNCTIONSIZECHECK_H

clang-tidy/readability/FunctionSizeCheck.cpp

 namespace tidy {
 namespace readability {
 namespace {
 
 class FunctionASTVisitor : public RecursiveASTVisitor<FunctionASTVisitor> {
   using Base = RecursiveASTVisitor<FunctionASTVisitor>;
 
 public:
+  bool VisitVarDecl(VarDecl *VD) {
+    // Do not count function params.
+    // Do not count decomposition declarations (C++17's structured bindings).
+    if (StructNesting == 0 &&
+        !(isa<ParmVarDecl>(VD) || isa<DecompositionDecl>(VD)))
+      ++Info.Variables;
+    return true;
+  }
+  bool VisitBindingDecl(BindingDecl *BD) {
+    // Do count each of the bindings (in the decomposition declaration).
+    if (StructNesting == 0)
+      ++Info.Variables;
+    return true;
+  }
+
   bool TraverseStmt(Stmt *Node) {
     if (!Node)
       return Base::TraverseStmt(Node);
 
     if (TrackedParent.back() && !isa<CompoundStmt>(Node))
       ++Info.Statements;
 
     switch (Node->getStmtClass()) {
public:
 
   bool TraverseDecl(Decl *Node) {
     TrackedParent.push_back(false);
     Base::TraverseDecl(Node);
     TrackedParent.pop_back();
     return true;
   }
 
+  bool TraverseLambdaExpr(LambdaExpr *Node) {
+    ++StructNesting;
+    Base::TraverseLambdaExpr(Node);
+    --StructNesting;
+    return true;
+  }
+
+  bool TraverseCXXRecordDecl(CXXRecordDecl *Node) {
+    ++StructNesting;
+    Base::TraverseCXXRecordDecl(Node);
+    --StructNesting;
+    return true;
+  }
+
+  bool TraverseStmtExpr(StmtExpr *SE) {
+    ++StructNesting;
+    Base::TraverseStmtExpr(SE);
+    --StructNesting;
+    return true;
+  }
+
   struct FunctionInfo {
     unsigned Lines = 0;
     unsigned Statements = 0;
     unsigned Branches = 0;
     unsigned NestingThreshold = 0;
+    unsigned Variables = 0;
     std::vector<SourceLocation> NestingThresholders;
   };
   FunctionInfo Info;
   std::vector<bool> TrackedParent;
+  unsigned StructNesting = 0;
   unsigned CurrentNestingLevel = 0;
 };
 
 } // namespace
 
 FunctionSizeCheck::FunctionSizeCheck(StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
       LineThreshold(Options.get("LineThreshold", -1U)),
       StatementThreshold(Options.get("StatementThreshold", 800U)),
       BranchThreshold(Options.get("BranchThreshold", -1U)),
       ParameterThreshold(Options.get("ParameterThreshold", -1U)),
-      NestingThreshold(Options.get("NestingThreshold", -1U)) {}
+      NestingThreshold(Options.get("NestingThreshold", -1U)),
+      VariableThreshold(Options.get("VariableThreshold", -1U)) {}
 
 void FunctionSizeCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "LineThreshold", LineThreshold);
   Options.store(Opts, "StatementThreshold", StatementThreshold);
   Options.store(Opts, "BranchThreshold", BranchThreshold);
   Options.store(Opts, "ParameterThreshold", ParameterThreshold);
   Options.store(Opts, "NestingThreshold", NestingThreshold);
+  Options.store(Opts, "VariableThreshold", VariableThreshold);
 }
 
 void FunctionSizeCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(functionDecl(unless(isInstantiated())).bind("func"), this);
 }
 
 void FunctionSizeCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *Func = Result.Nodes.getNodeAs<FunctionDecl>("func");
if (const Stmt *Body = Func->getBody()) {
     }
   }
 
   unsigned ActualNumberParameters = Func->getNumParams();
 
   if (FI.Lines > LineThreshold || FI.Statements > StatementThreshold ||
       FI.Branches > BranchThreshold ||
       ActualNumberParameters > ParameterThreshold ||
-      !FI.NestingThresholders.empty()) {
+      !FI.NestingThresholders.empty() || FI.Variables > VariableThreshold) {
     diag(Func->getLocation(),
          "function %0 exceeds recommended size/complexity thresholds")
         << Func;
   }
 
   if (FI.Lines > LineThreshold) {
     diag(Func->getLocation(),
          "%0 lines including whitespace and comments (threshold %1)",
diag(Func->getLocation(), "%0 parameters (threshold %1)",
         << ActualNumberParameters << ParameterThreshold;
   }
 
   for (const auto &CSPos : FI.NestingThresholders) {
     diag(CSPos, "nesting level %0 starts here (threshold %1)",
          DiagnosticIDs::Note)
         << NestingThreshold + 1 << NestingThreshold;
   }
+
+  if (FI.Variables > VariableThreshold) {
+    diag(Func->getLocation(), "%0 variables (threshold %1)",
+         DiagnosticIDs::Note)
+        << FI.Variables << VariableThreshold;
+  }
 }
 
 } // namespace readability
 } // namespace tidy
 } // namespace clang

docs/ReleaseNotes.rst

- New :doc:`portability-simd-intrinsics
   Warns or suggests alternatives if SIMD intrinsics are used which can be replaced by
   ``std::experimental::simd`` operations.
 
 - New :doc:`zircon-temporary-objects
   <clang-tidy/checks/zircon-temporary-objects>` check
 
   Warns on construction of specific temporary objects in the Zircon kernel.
 
 - New alias :doc:`hicpp-avoid-goto
   <clang-tidy/checks/hicpp-avoid-goto>` to :doc:`cppcoreguidelines-avoid-goto
   <clang-tidy/checks/cppcoreguidelines-avoid-goto>`
   added.
 
+- Added `VariableThreshold` option to :doc:`readability-function-size
+  <clang-tidy/checks/readability-function-size>` check
+
+  Flags functions that have more than a specified number of variables declared in the body.
+
 - Adding the missing bitwise assignment operations to 
   :doc:`hicpp-signed-bitwise <clang-tidy/checks/hicpp-signed-bitwise>`.
 
 - The 'misc-forwarding-reference-overload' check was renamed to :doc:`bugprone-forwarding-reference-overload
   <clang-tidy/checks/bugprone-forwarding-reference-overload>`
 
 - The 'misc-incorrect-roundings' check was renamed to :doc:`bugprone-incorrect-roundings
   <clang-tidy/checks/bugprone-incorrect-roundings>`

docs/clang-tidy/checks/readability-function-size.rst

.. option:: ParameterThreshold
    Flag functions that exceed a specified number of parameters. The default
    is `-1` (ignore the number of parameters).
 
 .. 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).
+
+.. option:: VariableThreshold
+
+   Flag functions exceeding this number of variables declared in the body.
+   The default is `-1` (ignore the number of variables).
+   Please note that function parameters and variables declared in lambdas,
+   GNU Statement Expressions, and nested class inline functions are not counted.

test/clang-tidy/readability-function-size-variables-c++17.cpp

+// RUN: %check_clang_tidy %s readability-function-size %t -- -config='{CheckOptions: [{key: readability-function-size.LineThreshold, value: 0}, {key: readability-function-size.StatementThreshold, value: 0}, {key: readability-function-size.BranchThreshold, value: 0}, {key: readability-function-size.ParameterThreshold, value: 5}, {key: readability-function-size.NestingThreshold, value: 2}, {key: readability-function-size.VariableThreshold, value: 1}]}' -- -std=c++17
+
+void structured_bindings() {
+  int a[2] = {1, 2};
+  auto [x, y] = a;
+}
+// CHECK-MESSAGES: :[[@LINE-4]]:6: warning: function 'structured_bindings' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 3 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 2 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 3 variables (threshold 1)
+
+#define SWAP(x, y) ({auto& [x0, x1] = x;  __typeof__(x) t = {x0, x1}; auto& [y0, y1] = y; auto& [t0, t1] = t; x0 = y0; x1 = y1; y0 = t0; y1 = t1; })
+void variables_13() {
+  int a[2] = {1, 2};
+  int b[2] = {3, 4};
+  SWAP(a, b);
+}
+// CHECK-MESSAGES: :[[@LINE-5]]:6: warning: function 'variables_13' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 4 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 11 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 2 variables (threshold 1)

test/clang-tidy/readability-function-size.cpp

-// RUN: %check_clang_tidy %s readability-function-size %t -- -config='{CheckOptions: [{key: readability-function-size.LineThreshold, value: 0}, {key: readability-function-size.StatementThreshold, value: 0}, {key: readability-function-size.BranchThreshold, value: 0}, {key: readability-function-size.ParameterThreshold, value: 5}, {key: readability-function-size.NestingThreshold, value: 2}]}' -- -std=c++11
+// RUN: %check_clang_tidy %s readability-function-size %t -- -config='{CheckOptions: [{key: readability-function-size.LineThreshold, value: 0}, {key: readability-function-size.StatementThreshold, value: 0}, {key: readability-function-size.BranchThreshold, value: 0}, {key: readability-function-size.ParameterThreshold, value: 5}, {key: readability-function-size.NestingThreshold, value: 2}, {key: readability-function-size.VariableThreshold, value: 1}]}' -- -std=c++11
 
 // Bad formatting is intentional, don't run clang-format over the whole file!
 
 void foo1() {
 }
 
 void foo2() {;}
 // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'foo2' exceeds recommended size/complexity thresholds [readability-function-size]

 //
 // CHECK-MESSAGES: :[[@LINE-4]]:30: warning: function 'barx' exceeds recommended size/complexity
 // CHECK-MESSAGES: :[[@LINE-5]]:30: note: 2 statements (threshold 0)
 
 #define macro() {int x; {int y; {int z;}}}
 
 void baz0() { // 1
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'baz0' exceeds recommended size/complexity
-  // CHECK-MESSAGES: :[[@LINE-2]]:6: note: 27 lines including whitespace and comments (threshold 0)
+  // CHECK-MESSAGES: :[[@LINE-2]]:6: note: 28 lines including whitespace and comments (threshold 0)
   // CHECK-MESSAGES: :[[@LINE-3]]:6: note: 9 statements (threshold 0)
   int a;
   { // 2
     int b;
     { // 3
 // CHECK-MESSAGES: :[[@LINE-1]]:5: note: nesting level 3 starts here (threshold 2)
       int c;
       { // 4
         int d;
       }
     }
   }
   { // 2
     int e;
   }
   { // 2
     { // 3
 // CHECK-MESSAGES: :[[@LINE-1]]:5: note: nesting level 3 starts here (threshold 2)
       int j;
     }
   }
   macro()
   // CHECK-MESSAGES: :[[@LINE-1]]:3: note: nesting level 3 starts here (threshold 2)
   // CHECK-MESSAGES: :[[@LINE-28]]:25: note: expanded from macro 'macro'
+  // CHECK-MESSAGES: :[[@LINE-27]]:6: note: 9 variables (threshold 1)
 }
 
 // check that nested if's are not reported. this was broken initially
 void nesting_if() { // 1
   // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'nesting_if' exceeds recommended size/complexity
-  // CHECK-MESSAGES: :[[@LINE-2]]:6: note: 22 lines including whitespace and comments (threshold 0)
+  // CHECK-MESSAGES: :[[@LINE-2]]:6: note: 23 lines including whitespace and comments (threshold 0)
   // CHECK-MESSAGES: :[[@LINE-3]]:6: note: 18 statements (threshold 0)
   // CHECK-MESSAGES: :[[@LINE-4]]:6: note: 6 branches (threshold 0)
   if (true) { // 2
      int j;
   } else if (true) { // 2
      int j;
      if (true) { // 3
        // CHECK-MESSAGES: :[[@LINE-1]]:16: note: nesting level 3 starts here (threshold 2)
        int j;
      }
   } else if (true) { // 2
      int j;
      if (true) { // 3
        // CHECK-MESSAGES: :[[@LINE-1]]:16: note: nesting level 3 starts here (threshold 2)
        int j;
      }
   } else if (true) { // 2
      int j;
   }
+  // CHECK-MESSAGES: :[[@LINE-22]]:6: note: 6 variables (threshold 1)
 }
 
 // however this should warn
 void bad_if_nesting() { // 1
 // CHECK-MESSAGES: :[[@LINE-1]]:6: warning: function 'bad_if_nesting' exceeds recommended size/complexity
-// CHECK-MESSAGES: :[[@LINE-2]]:6: note: 22 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-2]]:6: note: 23 lines including whitespace and comments (threshold 0)
 // CHECK-MESSAGES: :[[@LINE-3]]:6: note: 12 statements (threshold 0)
 // CHECK-MESSAGES: :[[@LINE-4]]:6: note: 4 branches (threshold 0)
   if (true) {    // 2
     int j;
   } else { // 2
     if (true) { // 3
       // CHECK-MESSAGES: :[[@LINE-1]]:15: note: nesting level 3 starts here (threshold 2)
       int j;
     } else { // 3
       // CHECK-MESSAGES: :[[@LINE-1]]:12: note: nesting level 3 starts here (threshold 2)
       if (true) { // 4
         int j;
       } else { // 4
         if (true) { // 5
           int j;
         }
       }
     }
   }
+  // CHECK-MESSAGES: :[[@LINE-22]]:6: note: 4 variables (threshold 1)
 }
+
+void variables_0() {
+  int i;
+}
+// CHECK-MESSAGES: :[[@LINE-3]]:6: warning: function 'variables_0' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-4]]:6: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 1 statements (threshold 0)
+void variables_1(int i) {
+  int j;
+}
+// CHECK-MESSAGES: :[[@LINE-3]]:6: warning: function 'variables_1' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-4]]:6: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 1 statements (threshold 0)
+void variables_2(int i, int j) {
+  ;
+}
+// CHECK-MESSAGES: :[[@LINE-3]]:6: warning: function 'variables_2' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-4]]:6: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 1 statements (threshold 0)
+void variables_3() {
+  int i[2];
+}
+// CHECK-MESSAGES: :[[@LINE-3]]:6: warning: function 'variables_3' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-4]]:6: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 1 statements (threshold 0)
+void variables_4() {
+  int i;
+  int j;
+}
+// CHECK-MESSAGES: :[[@LINE-4]]:6: warning: function 'variables_4' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 3 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 2 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 2 variables (threshold 1)
+void variables_5() {
+  int i, j;
+}
+// CHECK-MESSAGES: :[[@LINE-3]]:6: warning: function 'variables_5' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-4]]:6: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 1 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 2 variables (threshold 1)
+void variables_6() {
+  for (int i;;)
+    for (int j;;)
+      ;
+}
+// CHECK-MESSAGES: :[[@LINE-5]]:6: warning: function 'variables_6' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 4 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 5 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 2 branches (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-9]]:6: note: 2 variables (threshold 1)
+void variables_7() {
+  if (int a = 1)
+    if (int b = 2)
+      ;
+}
+// CHECK-MESSAGES: :[[@LINE-5]]:6: warning: function 'variables_7' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 4 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 7 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 2 branches (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-9]]:6: note: 2 variables (threshold 1)
+void variables_8() {
+  int a[2];
+  for (auto i : a)
+    for (auto j : a)
+      ;
+}
+// CHECK-MESSAGES: :[[@LINE-6]]:6: warning: function 'variables_8' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 5 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 8 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-9]]:6: note: 2 branches (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-10]]:6: note: 3 variables (threshold 1)
+void variables_9() {
+  int a, b;
+  struct A {
+    A(int c, int d) {
+      int e, f;
+    }
+  };
+}
+// CHECK-MESSAGES: :[[@LINE-8]]:6: warning: function 'variables_9' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-9]]:6: note: 7 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-10]]:6: note: 3 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-11]]:6: note: 2 variables (threshold 1)
+// CHECK-MESSAGES: :[[@LINE-9]]:5: warning: function 'A' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-10]]:5: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-11]]:5: note: 1 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-12]]:5: note: 2 variables (threshold 1)
+void variables_10() {
+  int a, b;
+  struct A {
+    int c;
+    int d;
+  };
+}
+// CHECK-MESSAGES: :[[@LINE-7]]:6: warning: function 'variables_10' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 6 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-9]]:6: note: 2 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-10]]:6: note: 2 variables (threshold 1)
+void variables_11() {
+  struct S {
+    void bar() {
+      int a, b;
+    }
+  };
+}
+// CHECK-MESSAGES: :[[@LINE-7]]:6: warning: function 'variables_11' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 6 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:10: warning: function 'bar' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-8]]:10: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-9]]:10: note: 2 variables (threshold 1)
+void variables_12() {
+  int v;
+  auto test = [](int a, int b) -> void {};
+  test({}, {});
+}
+// CHECK-MESSAGES: :[[@LINE-5]]:6: warning: function 'variables_12' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 4 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 3 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-8]]:6: note: 2 variables (threshold 1)
+void variables_13() {
+  int v;
+  auto test = []() -> void {
+    int a;
+    int b;
+  };
+  test();
+}
+// CHECK-MESSAGES: :[[@LINE-8]]:6: warning: function 'variables_13' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-9]]:6: note: 7 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-10]]:6: note: 5 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-11]]:6: note: 2 variables (threshold 1)
+void variables_14() {
+  (void)({int a = 12; a; });
+  (void)({int a = 12; a; });
+}
+// CHECK-MESSAGES: :[[@LINE-4]]:6: warning: function 'variables_14' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 3 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 6 statements (threshold 0)
+#define SWAP(x, y) ({__typeof__(x) temp = x; x = y; y = temp; })
+void variables_15() {
+  int a = 10, b = 12;
+  SWAP(a, b);
+}
+// CHECK-MESSAGES: :[[@LINE-4]]:6: warning: function 'variables_15' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 3 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 5 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 2 variables (threshold 1)
+#define vardecl(type, name) type name;
+void variables_16() {
+  vardecl(int, a);
+  vardecl(int, b);
+}
+// CHECK-MESSAGES: :[[@LINE-4]]:6: warning: function 'variables_16' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-5]]:6: note: 3 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-6]]:6: note: 4 statements (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-7]]:6: note: 2 variables (threshold 1)