[clang-tools-extra] [clang-tidy] Add modernize-use-std-format check (PR #90397)

[Danny Mösch via cfe-commits]

================
@@ -0,0 +1,84 @@
+.. title:: clang-tidy - modernize-use-std-format
+
+modernize-use-std-format
+========================
+
+Converts calls to ``absl::StrFormat``, or other functions via
+configuration options, to C++20's ``std::format``, or another function
+via a configuration option, modifying the format string appropriately and
+removing now-unnecessary calls to ``std::string::c_str()`` and
+``std::string::data()``.
+
+In other words, it turns lines like:
+
+.. code-block:: c++
+
+  return absl::StrFormat("The %s is %3d\n", description.c_str(), value);
+
+into:
+
+.. code-block:: c++
+
+  return std::format("The {} is {:3}", description, value);
+
+The check uses the same format-string-conversion algorithm as
+`modernize-use-std-print <../modernize/use-std-print.html>`_ and its
+shortcomings are described in the documentation for that check.
+
+Options
+-------
+
+.. option:: StrictMode
+
+   When `true`, the check will add casts when converting from variadic
+   functions and printing signed or unsigned integer types (including
+   fixed-width integer types from ``<cstdint>``, ``ptrdiff_t``, ``size_t``
+   and ``ssize_t``) as the opposite signedness to ensure that the output
+   would matches that of a simple wrapper for ``std::sprintf`` that
+   accepted a C-style variable argument list. For example, with
+   `StrictMode` enabled:
+
+  .. code-block:: c++
+
+    extern std::string strprintf(const char *format, ...);
+    int i = -42;
+    unsigned int u = 0xffffffff;
+    return strprintf("%d %u\n", i, u);
+
+  would be converted to:
----------------
SimplyDanny wrote:

```suggestion
  would be converted to
```

https://github.com/llvm/llvm-project/pull/90397