Add error for duplicate modular_format aspects and tests

Author: mysterymath

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -13066,6 +13066,9 @@ def err_get_vtable_pointer_requires_complete_type
 def err_modular_format_attribute_no_format
     : Error<"'modular_format' attribute requires 'format' attribute">;
 
+def err_modular_format_duplicate_aspect
+    : Error<"duplicate aspect '%0' in 'modular_format' attribute">;
+
 // SYCL-specific diagnostics
 def warn_sycl_kernel_num_of_template_params : Warning<
   "'sycl_kernel' attribute only applies to a function template with at least"

clang/lib/Sema/SemaDeclAttr.cpp

@@ -6978,16 +6978,27 @@ static void handleModularFormat(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (!S.checkStringLiteralArgumentAttr(AL, 1, ImplName))
     return;
   SmallVector<StringRef> Aspects;
+  llvm::DenseSet<StringRef> SeenAspects;
+  bool HasDuplicate = false;
   for (unsigned I = 2, E = AL.getNumArgs(); I != E; ++I) {
     StringRef Aspect;
     if (!S.checkStringLiteralArgumentAttr(AL, I, Aspect))
       return;
+    if (!SeenAspects.insert(Aspect).second) {
+      S.Diag(AL.getArgAsExpr(I)->getExprLoc(),
+             diag::err_modular_format_duplicate_aspect)
+          << Aspect;
+      HasDuplicate = true;
+      continue;
+    }
     Aspects.push_back(Aspect);
   }
 
-  // Store aspects sorted and without duplicates.
+  if (HasDuplicate)
+    return;
+
+  // Store aspects sorted.
   llvm::sort(Aspects);
-  Aspects.erase(llvm::unique(Aspects), Aspects.end());
 
   D->addAttr(::new (S.Context) ModularFormatAttr(
       S.Context, AL, AL.getArgAsIdent(0)->getIdentifierInfo(), ImplName,

clang/test/Sema/attr-modular-format.c

@@ -3,3 +3,7 @@
 int printf(const char *fmt, ...)  __attribute__((modular_format(__modular_printf, "__printf", "float")));  // no-error
 int myprintf(const char *fmt, ...)  __attribute__((modular_format(__modular_printf, "__printf", "float")));  // expected-error {{'modular_format' attribute requires 'format' attribute}}
 
+int dupe(const char *fmt, ...)  __attribute__((modular_format(__modular_printf, "__printf", "float", "int", "float"), format(printf, 1, 2))); // expected-error {{duplicate aspect 'float' in 'modular_format' attribute}}
+int multi_dupe(const char *fmt, ...)  __attribute__((modular_format(__modular_printf, "__printf", "float", "int", "float", "int"), format(printf, 1, 2))); // expected-error {{duplicate aspect 'float' in 'modular_format' attribute}} \
+                                                                                                                                                                 // expected-error {{duplicate aspect 'int' in 'modular_format' attribute}}
+