llvm-formatv-string

Validates llvm::formatv format strings against the provided arguments, diagnosing mismatched argument counts, unused arguments, and mixed index styles.

This check diagnoses the following issues:

• The number of replacement indices in the format string does not match the number of arguments provided.

• A format string does not use one of the given arguments.

• Mixing of automatic and explicit indices (e.g. {} {1}).

// warning: format string requires 2 arguments, but 1 argument was provided
llvm::formatv("{0} {1}", x);

// warning: format string mixes automatic and explicit indices
llvm::formatv("{} {1}", x, y);

// warning: argument unused in format string
llvm::formatv("{0} {2}", x, y, z);

// OK.
llvm::formatv("{0} {1}", x, y);
llvm::formatv("{} {}", x, y);
llvm::formatv("{0} {0}", x);

The check only operates on calls where the format string is a string literal. Dynamic format strings are not diagnosed.

Options

AdditionalFunctions

A semicolon-separated list of additional fully qualified function names to check, beyond llvm::formatv and llvm::createStringErrorV. Each function must be a variadic template whose last parameter is a parameter pack. The format string is assumed to be the parameter immediately preceding the pack.

For example, to check ::mylib::log(Level, const char *Fmt, Ts&&...) set this option to ::mylib::log.

Default is the empty string.