[clang-tidy] modernize-avoid-c-arrays: avoid main function (PR40604)

Summary:
The check should ignore the main function, the program entry point.
It is not possible to use `std::array<>` for the `argv`.
The alternative is to use `char** argv`.

Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=40604 | PR40604 ]]

Reviewers: JonasToth, aaron.ballman

Reviewed By: aaron.ballman

Subscribers: xazax.hun, hans, cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D57787

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@353327 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 50 insertions, 1 deletions

diff --git a/clang-tidy/modernize/AvoidCArraysCheck.cpp b/clang-tidy/modernize/AvoidCArraysCheck.cpp
index bceda5c2..e3dffd06 100644
--- a/clang-tidy/modernize/AvoidCArraysCheck.cpp
+++ b/clang-tidy/modernize/AvoidCArraysCheck.cpp
@@ -30,6 +30,12 @@ AST_MATCHER(clang::RecordDecl, isExternCContext) {
   return Node.isExternCContext();
 }
 
+AST_MATCHER(clang::ParmVarDecl, isArgvOfMain) {
+  const clang::DeclContext *DC = Node.getDeclContext();
+  const auto *FD = llvm::dyn_cast<clang::FunctionDecl>(DC);
+  return FD ? FD->isMain() : false;
+}
+
 } // namespace
 
 namespace clang {
@@ -43,7 +49,8 @@ void AvoidCArraysCheck::registerMatchers(MatchFinder *Finder) {
 
   Finder->addMatcher(
       typeLoc(hasValidBeginLoc(), hasType(arrayType()),
-              unless(anyOf(hasParent(varDecl(isExternC())),
+              unless(anyOf(hasParent(parmVarDecl(isArgvOfMain())),
+                           hasParent(varDecl(isExternC())),
                            hasParent(fieldDecl(
                                hasParent(recordDecl(isExternCContext())))),
                            hasAncestor(functionDecl(isExternC())))))
diff --git a/docs/clang-tidy/checks/modernize-avoid-c-arrays.rst b/docs/clang-tidy/checks/modernize-avoid-c-arrays.rst
index 8f856a52..d7bc7474 100644
--- a/docs/clang-tidy/checks/modernize-avoid-c-arrays.rst
+++ b/docs/clang-tidy/checks/modernize-avoid-c-arrays.rst
@@ -54,3 +54,7 @@ such headers between C code, and C++ code.
   }
 
   }
+
+Similarly, the ``main()`` function is ignored. Its second and third parameters
+can be either ``char* argv[]`` or ``char** argv``, but can not be
+``std::array<>``.
diff --git a/test/clang-tidy/modernize-avoid-c-arrays-ignores-main.cpp b/test/clang-tidy/modernize-avoid-c-arrays-ignores-main.cpp
new file mode 100644
index 00000000..6549422f
--- /dev/null
+++ b/test/clang-tidy/modernize-avoid-c-arrays-ignores-main.cpp
@@ -0,0 +1,18 @@
+// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t
+
+int not_main(int argc, char *argv[]) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style arrays, use std::array<> instead
+  int f4[] = {1, 2};
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
+}
+
+int main(int argc, char *argv[]) {
+  int f5[] = {1, 2};
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
+
+  auto not_main = [](int argc, char *argv[]) {
+    // CHECK-MESSAGES: :[[@LINE-1]]:32: warning: do not declare C-style arrays, use std::array<> instead
+    int f6[] = {1, 2};
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not declare C-style arrays, use std::array<> instead
+  };
+}
diff --git a/test/clang-tidy/modernize-avoid-c-arrays-ignores-three-arg-main.cpp b/test/clang-tidy/modernize-avoid-c-arrays-ignores-three-arg-main.cpp
new file mode 100644
index 00000000..22a4016f
--- /dev/null
+++ b/test/clang-tidy/modernize-avoid-c-arrays-ignores-three-arg-main.cpp
@@ -0,0 +1,20 @@
+// RUN: %check_clang_tidy %s modernize-avoid-c-arrays %t
+
+int not_main(int argc, char *argv[], char *argw[]) {
+  // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: do not declare C-style arrays, use std::array<> instead
+  // CHECK-MESSAGES: :[[@LINE-2]]:38: warning: do not declare C-style arrays, use std::array<> instead
+  int f4[] = {1, 2};
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
+}
+
+int main(int argc, char *argv[], char *argw[]) {
+  int f5[] = {1, 2};
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: do not declare C-style arrays, use std::array<> instead
+
+  auto not_main = [](int argc, char *argv[], char *argw[]) {
+    // CHECK-MESSAGES: :[[@LINE-1]]:32: warning: do not declare C-style arrays, use std::array<> instead
+    // CHECK-MESSAGES: :[[@LINE-2]]:46: warning: do not declare C-style arrays, use std::array<> instead
+    int f6[] = {1, 2};
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: do not declare C-style arrays, use std::array<> instead
+  };
+}