Add support for -Wchar-subscripts. Fixes PR4801.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@81747 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 60 insertions, 1 deletions

diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index d00ad6915f..0901636335 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -106,6 +106,7 @@ def : DiagGroup<"variadic-macros">;
 def VectorConversions : DiagGroup<"vector-conversions">;      // clang specific
 def VolatileRegisterVar : DiagGroup<"volatile-register-var">;
 def : DiagGroup<"write-strings">;
+def CharSubscript : DiagGroup<"char-subscripts">;
 
 // Aggregation warning settings.
 
@@ -142,7 +143,8 @@ def Most : DiagGroup<"most", [
     UnusedVariable,
     VectorConversions,
     VolatileRegisterVar,
-    Reorder
+    Reorder,
+    CharSubscript
  ]>;
 
 // -Wall is -Wmost -Wparentheses
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index ab12463cc0..db60455873 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1319,6 +1319,8 @@ def err_typecheck_member_reference_unknown : Error<
   "cannot refer to member %0 with '%select{.|->}1'">;
 def note_member_reference_needs_call : Note<
   "perhaps you meant to call this function with '()'?">;
+def warn_subscript_is_char : Warning<"array subscript is of type 'char'">,
+  InGroup<CharSubscript>, DefaultIgnore;
 
 def err_typecheck_incomplete_tag : Error<"incomplete definition of type %0">;
 def err_typecheck_no_member_deprecated : Error<"no member named %0">;
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 11bd323011..32d3e06e3e 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -1809,6 +1809,9 @@ Sema::ActOnArraySubscriptExpr(Scope *S, ExprArg Base, SourceLocation LLoc,
     return ExprError(Diag(LLoc, diag::err_typecheck_subscript_not_integer)
                      << IndexExpr->getSourceRange());
 
+  if (IndexExpr->getType()->isCharType() && !IndexExpr->isTypeDependent())
+    Diag(LLoc, diag::warn_subscript_is_char) << IndexExpr->getSourceRange();
+
   // C99 6.5.2.1p1: "shall have type "pointer to *object* type". Similarly,
   // C++ [expr.sub]p1: The type "T" shall be a completely-defined object
   // type. Note that Functions are not objects, and that (in C99 parlance)
diff --git a/test/Sema/warn-char-subscripts.c b/test/Sema/warn-char-subscripts.c
new file mode 100644
index 0000000000..65a34e8fc2
--- /dev/null
+++ b/test/Sema/warn-char-subscripts.c
@@ -0,0 +1,31 @@
+// RUN: clang-cc -Wchar-subscripts -fsyntax-only -verify %s
+
+void t1() {
+  int array[1] = { 0 };
+  char subscript = 0;
+  int val = array[subscript]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t2() {
+  int array[1] = { 0 };
+  char subscript = 0;
+  int val = subscript[array]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t3() {
+  int *array = 0;
+  char subscript = 0;
+  int val = array[subscript]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void t4() {
+  int *array = 0;
+  char subscript = 0;
+  int val = subscript[array]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+char returnsChar();
+void t5() {
+  int *array = 0;
+  int val = array[returnsChar()]; // expected-warning{{array subscript is of type 'char'}}
+}
diff --git a/test/SemaCXX/warn-char-subscripts.cpp b/test/SemaCXX/warn-char-subscripts.cpp
new file mode 100644
index 0000000000..1c06db91c3
--- /dev/null
+++ b/test/SemaCXX/warn-char-subscripts.cpp
@@ -0,0 +1,21 @@
+// RUN: clang-cc -Wchar-subscripts -fsyntax-only -verify %s
+
+template<typename T>
+void t1() {
+  int array[1] = { 0 };
+  T subscript = 0;
+  int val = array[subscript]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+template<typename T>
+void t2() {
+  int array[1] = { 0 };
+  T subscript = 0;
+  int val = subscript[array]; // expected-warning{{array subscript is of type 'char'}}
+}
+
+void test() {
+  t1<char>(); // expected-note {{in instantiation of function template specialization 't1<char>' requested here}}
+  t2<char>(); // expected-note {{in instantiation of function template specialization 't2<char>' requested here}}
+}
+