Detect when the buffer is a member access, fix tests

Add a case for when it's a member variable access and we can statically
determine the size. Also add new test to ensure the change works
reliably and update old tests to not expect this warning.

Author: mxms

clang/lib/Analysis/UnsafeBufferUsage.cpp

@@ -466,7 +466,7 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
   // Array index wasn't an integer literal, let's see if it was an enum or
   // something similar
   const auto IntConst = Node.getIdx()->getIntegerConstantExpr(Finder->getASTContext());
-  if (IntConst && *IntConst > 0 && *IntConst < size) {
+  if (IntConst && *IntConst >= 0 && *IntConst < size) {
     return true;
   }
 

clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp

@@ -47,8 +47,11 @@ enum FooEnum {
 };
 
 void constant_enum_safe() {
-  int buffer[FooEnum::D] = { 0, 1, 2 };
+  int buffer[FooEnum::D] = { 0, 1, 2 }; // expected-warning{{'buffer' is an unsafe buffer that does not perform bounds checks}}
+                                        // expected-note@-1{{change type of 'buffer' to 'std::array' to label it for hardening}}
+  buffer[A] = 0; // no-warning
   buffer[C] = 0; // no-warning
+  buffer[D] = 0; // expected-note{{used in buffer access here}}
 }
 
 void constant_enum_unsafe(FooEnum e) {

clang/test/SemaCXX/warn-unsafe-buffer-usage-field-attr.cpp

@@ -96,7 +96,6 @@ void test_attribute_multiple_fields (D d) {
 
    int v = d.buf[0]; //expected-warning{{field 'buf' prone to unsafe buffer manipulation}}
 
-   //expected-warning@+1{{unsafe buffer access}}
    v = d.buf[5]; //expected-warning{{field 'buf' prone to unsafe buffer manipulation}}
 }
 

clang/test/SemaCXX/warn-unsafe-buffer-usage.cpp

@@ -128,25 +128,25 @@ T_t funRetT();
 T_t * funRetTStar();
 
 void testStructMembers(struct T * sp, struct T s, T_t * sp2, T_t s2) {
-  foo(sp->a[1],     // expected-warning{{unsafe buffer access}}
+  foo(sp->a[1],
       sp->b[1],     // expected-warning{{unsafe buffer access}}
-      sp->c.a[1],   // expected-warning{{unsafe buffer access}}
+      sp->c.a[1],
       sp->c.b[1],   // expected-warning{{unsafe buffer access}}
-      s.a[1],       // expected-warning{{unsafe buffer access}}
+      s.a[1],
       s.b[1],       // expected-warning{{unsafe buffer access}}
-      s.c.a[1],     // expected-warning{{unsafe buffer access}}
+      s.c.a[1],
       s.c.b[1],     // expected-warning{{unsafe buffer access}}
-      sp2->a[1],    // expected-warning{{unsafe buffer access}}
+      sp2->a[1],
       sp2->b[1],    // expected-warning{{unsafe buffer access}}
-      sp2->c.a[1],  // expected-warning{{unsafe buffer access}}
+      sp2->c.a[1],
       sp2->c.b[1],  // expected-warning{{unsafe buffer access}}
-      s2.a[1],      // expected-warning{{unsafe buffer access}}
+      s2.a[1],
       s2.b[1],      // expected-warning{{unsafe buffer access}}
-      s2.c.a[1],           // expected-warning{{unsafe buffer access}}
+      s2.c.a[1],
       s2.c.b[1],           // expected-warning{{unsafe buffer access}}
-      funRetT().a[1],      // expected-warning{{unsafe buffer access}}
+      funRetT().a[1],
       funRetT().b[1],      // expected-warning{{unsafe buffer access}}
-      funRetTStar()->a[1], // expected-warning{{unsafe buffer access}}
+      funRetTStar()->a[1],
       funRetTStar()->b[1]  // expected-warning{{unsafe buffer access}}
       );
 }
@@ -213,7 +213,6 @@ void testTypedefs(T_ptr_t p) {
   // expected-warning@-1{{'p' is an unsafe pointer used for buffer access}}
   foo(p[1],       // expected-note{{used in buffer access here}}
       p[1].a[1],  // expected-note{{used in buffer access here}}
-                  // expected-warning@-1{{unsafe buffer access}}
       p[1].b[1]   // expected-note{{used in buffer access here}}
                   // expected-warning@-1{{unsafe buffer access}}
       );