[clang-tools-extra] [clang-tidy] Improve `readability-function-size`: count class member initializers as statements (PR #131669)

[Baranov Victor via cfe-commits]

https://github.com/vbvictor created https://github.com/llvm/llvm-project/pull/131669

Improve `readability-function-size` by counting class member initializers as statements.
Relates to https://github.com/llvm/llvm-project/issues/131126#issuecomment-2725906714.

This PR in draft state until https://github.com/llvm/llvm-project/pull/131406 is merged.


>From eb75bd2c7cd2645c2371d512c4e78b17d18935e8 Mon Sep 17 00:00:00 2001
From: Victor Baranov <bar.victor.2002 at gmail.com>
Date: Mon, 17 Mar 2025 23:25:10 +0300
Subject: [PATCH] add traverse of ctor-initializers as statements

---
 .../readability/FunctionSizeCheck.cpp         |  6 ++++++
 clang-tools-extra/docs/ReleaseNotes.rst       |  4 ++++
 .../checkers/readability/function-size.cpp    | 20 +++++++++++++++++++
 3 files changed, 30 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/readability/FunctionSizeCheck.cpp b/clang-tools-extra/clang-tidy/readability/FunctionSizeCheck.cpp
index 3313bcb39b7f3..a313d65b5d84c 100644
--- a/clang-tools-extra/clang-tidy/readability/FunctionSizeCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/FunctionSizeCheck.cpp
@@ -108,6 +108,12 @@ class FunctionASTVisitor : public RecursiveASTVisitor<FunctionASTVisitor> {
     return true;
   }
 
+  bool TraverseConstructorInitializer(CXXCtorInitializer *Init) {
+    ++Info.Statements;
+    Base::TraverseConstructorInitializer(Init);
+    return true;
+  }
+
   struct FunctionInfo {
     unsigned Lines = 0;
     unsigned Statements = 0;
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 0ad52f83fad85..a41ec3757afbe 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -178,6 +178,10 @@ Changes in existing checks
   tolerating fix-it breaking compilation when functions is used as pointers
   to avoid matching usage of functions within the current compilation unit.
 
+- Improved :doc:`readability-function-size
+  <clang-tidy/checks/readability/function-size>` check by counting member
+  initializers in constructors as statements.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/function-size.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/function-size.cpp
index 45b2604b43d03..a9557788f1d75 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/readability/function-size.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/function-size.cpp
@@ -319,3 +319,23 @@ void variables_16() {
 // 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)
+
+struct A {
+  A(int c, int d) : a(0), b(c) {}
+  int a;
+  int b;
+};
+// CHECK-MESSAGES: :[[@LINE-4]]:3: warning: function 'A' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-5]]:3: note: 2 statements (threshold 0)
+
+struct B {
+  B(int x, int y, int z) : a(x + y * z), b(), c_a(y, z) {
+    ;
+  }
+  int a;
+  int b;
+  A c_a;
+};
+// CHECK-MESSAGES: :[[@LINE-7]]:3: warning: function 'B' exceeds recommended size/complexity thresholds [readability-function-size]
+// CHECK-MESSAGES: :[[@LINE-8]]:3: note: 2 lines including whitespace and comments (threshold 0)
+// CHECK-MESSAGES: :[[@LINE-9]]:3: note: 4 statements (threshold 0)