https://github.com/JonasToth updated
https://github.com/llvm/llvm-project/pull/118209
>From f4345664e10ac6a9e87b33b1e816b685a1355bb6 Mon Sep 17 00:00:00 2001
From: Jonas Toth <developm...@jonas-toth.eu>
Date: Sun, 1 Dec 2024 12:02:13 +0100
Subject: [PATCH] [clang-tidy][docs] improve documentation on
cppcoreguidelines-narrowing-conversions (#111510)
---
.../narrowing-conversions.rst | 33 +++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git
a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst
b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst
index 04260e75aa558f..6b0c3187b40874 100644
---
a/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst
+++
b/clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/narrowing-conversions.rst
@@ -27,6 +27,39 @@ This check will flag:
- All applications of binary operators with a narrowing conversions.
For example: ``int i; i+= 0.1;``.
+Arithmetic with smaller integer types than ``int`` trigger implicit
conversions,
+as explained under `"Integral Promotion" on cppreference.com
+<https://en.cppreference.com/w/cpp/language/implicit_conversion>`_.
+This check diagnoses more instances of narrowing than the compiler warning
+`-Wconversion` does. The example below demonstrates this behavior.
+
+.. code-block:: c++
+
+ // The following function definition demonstrates usage of arithmetic with
+ // integer types smaller than `int` and how the narrowing conversion happens
+ // implicitly.
+ void computation(short argument1, short argument2) {
+ // Arithmetic written by humans:
+ short result = argument1 + argument2;
+ // Arithmetic actually performed by C++:
+ short result = static_cast<short>(static_cast<int>(argument1) +
static_cast<int>(argument2));
+ }
+
+ void recommended_resolution(short argument1, short argument2) {
+ short result = argument1 + argument2;
+ // ^ warning: narrowing conversion from 'int' to signed type
'short' is implementation-defined
+
+ // The recommended way to resolve this issue with the GSL is one of two
ways.
+ // Either by a cast that throws if a loss of precision would occur.
+ short result = gsl::narrow<short>(argument1 + argument2);
+ // Or it can be resolved without checking the result.
+ short result = gsl::narrow_cast<short>(argument1 + argument2);
+
+ // A classical `static_cast` will silence the warning as well if the GSL
+ // is not available.
+ short result = static_cast<short>(argument1 + argument2);
+ }
+
Options
-------
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