[clang-tidy] readability-redundant-declaration: fix false positive with C "extern inline"

Summary:
readability-redundant-declaration was diagnosing a redundant declaration
on "extern inline void f();", which is needed in C code to force an external definition
of the inline function f. (This is different to how inline behaves in C++).

Reviewers: alexfh, danielmarjamaki

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D61700

llvm-svn: 360613

clang-tools-extra/clang-tidy/readability/RedundantDeclarationCheck.cpp

@@ -17,6 +17,10 @@ namespace clang {
 namespace tidy {
 namespace readability {
 
+AST_MATCHER(FunctionDecl, doesDeclarationForceExternallyVisibleDefinition) {
+  return Node.doesDeclarationForceExternallyVisibleDefinition();
+}
+
 RedundantDeclarationCheck::RedundantDeclarationCheck(StringRef Name,
                                                      ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
@@ -25,7 +29,9 @@ RedundantDeclarationCheck::RedundantDeclarationCheck(StringRef Name,
 void RedundantDeclarationCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(
       namedDecl(anyOf(varDecl(unless(isDefinition())),
-                      functionDecl(unless(anyOf(isDefinition(), isDefaulted(),
+                      functionDecl(unless(anyOf(
+                          isDefinition(), isDefaulted(),
+                          doesDeclarationForceExternallyVisibleDefinition(),
                           hasParent(friendDecl()))))))
           .bind("Decl"),
       this);

clang-tools-extra/test/clang-tidy/readability-redundant-declaration.c

@@ -0,0 +1,31 @@
+// RUN: %check_clang_tidy %s readability-redundant-declaration %t
+
+extern int Xyz;
+extern int Xyz; // Xyz
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'Xyz' declaration [readability-redundant-declaration]
+// CHECK-FIXES: {{^}}// Xyz{{$}}
+int Xyz = 123;
+
+extern int A;
+extern int A, B;
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'A' declaration
+// CHECK-FIXES: {{^}}extern int A, B;{{$}}
+
+extern int Buf[10];
+extern int Buf[10]; // Buf[10]
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'Buf' declaration
+// CHECK-FIXES: {{^}}// Buf[10]{{$}}
+
+static int f();
+static int f(); // f
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'f' declaration
+// CHECK-FIXES: {{^}}// f{{$}}
+static int f() {}
+
+inline void g() {}
+
+inline void g();
+// CHECK-MESSAGES: :[[@LINE-1]]:13: warning: redundant 'g' declaration
+
+// OK: Needed to emit an external definition.
+extern inline void g();

clang-tools-extra/test/clang-tidy/readability-redundant-declaration.cpp

@@ -68,3 +68,13 @@ DEFINE(test);
 // CHECK-FIXES: {{^}}DEFINE(test);{{$}}
 
 } // namespace macros
+
+inline void g() {}
+
+inline void g(); // g
+// CHECK-MESSAGES: :[[@LINE-1]]:13: warning: redundant 'g' declaration
+// CHECK-FIXES: {{^}}// g{{$}}
+
+extern inline void g(); // extern g
+// CHECK-MESSAGES: :[[@LINE-1]]:20: warning: redundant 'g' declaration
+// CHECK-FIXES: {{^}}// extern g{{$}}