[Sema] check InitListExpr format strings like {"foo"}

[inclyc]

Summary

Adds InitListExpr case in format string checks.

e.g.

int sprintf(char *__restrict, const char * __restrict, ...);

int foo()
{
    char data[100];
    constexpr const char* fmt2{"%d"};  // no-warning
    sprintf(data, fmt2, 123);
}

Fixes: https://github.com/llvm/llvm-project/issues/58900

[inclyc]

ping :)

[inclyc]

Do we need release notes here? This patch is just an improvement to https://reviews.llvm.org/D130906

[aaron.ballman]

In D137839#3944574, @inclyc wrote:

Do we need release notes here? This patch is just an improvement to https://reviews.llvm.org/D130906

I don't think we need release notes in this case, the existing ones work well enough.

LGTM with a request for an additional test case (you can add it when you land the changes, I don't expect surprises from the test, it's just for regression coverage).

clang/test/SemaCXX/format-strings.cpp

208

Cam you also add a test case for:

printf(fmt, "oops", 1.0f);

to show that we still issue diagnostics when they're appropriate?

[inclyc]

Address comments

• add a test to coverage warnings if appropriate

clang/lib/Sema/SemaChecking.cpp

tryAgain:
   if (E->isNullPointerConstant(S.Context, Expr::NPC_ValueDependentIsNotNull))
     // Technically -Wformat-nonliteral does not warn about this case.
     // The behavior of printf and friends in this case is implementation
     // dependent.  Ideally if the format string cannot be null then
     // it should have a 'nonnull' attribute in the function prototype.
     return SLCT_UncheckedLiteral;
 
   switch (E->getStmtClass()) {
+  case Stmt::InitListExprClass:
+    // Handle expressions like {"foobar"}.
+    if (const clang::Expr *SLE = maybeConstEvalStringLiteral(S.Context, E)) {
+      return checkFormatStringExpr(S, SLE, Args, APK, format_idx, firstDataArg,
+                                   Type, CallType, /*InFunctionCall*/ false,
+                                   CheckedVarArgs, UncoveredArg, Offset,
+                                   IgnoreStringsWithoutSpecifiers);
+    }
+    return SLCT_NotALiteral;
   case Stmt::BinaryConditionalOperatorClass:
   case Stmt::ConditionalOperatorClass: {
     // The expression is a literal if both sub-expressions were, and it was
     // completely checked only if both sub-expressions were checked.
     const AbstractConditionalOperator *C =
         cast<AbstractConditionalOperator>(E);
 
     // Determine whether it is necessary to check both sub-expressions, for

clang/test/SemaCXX/format-strings.cpp

 
 
 void f() {
   printf(basic(), 1, 2); // expected-warning {{format specifies type 'char *' but the argument has type 'int'}}
   printf(correct_fmt(), 1, 2);
   printf(string_linebreak(), 1, 2, 3, 4); // expected-warning {{format specifies type 'char *' but the argument has type 'int'}}
   printf(not_literal(), 1, 2, 3, 4); // expected-warning {{format string is not a string literal}}
   printf(wrap_constexpr(), 1, 2); // expected-warning {{format specifies type 'char *' but the argument has type 'int'}}
+
+  constexpr const char *fmt {"%d%d"};
+  printf(fmt, 1, 1); // no-warning
+
+  constexpr const char *fmt2 {"%d"}; // expected-note{{format string is defined here}}
+  printf(fmt2, "oops"); // expected-warning{{format specifies type 'int' but the argument has type}}
 }
 
 
 }
 #endif