Endre =?utf-8?q?Fülöp?= <[email protected]>,
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Endre =?utf-8?q?Fülöp?= <[email protected]>,
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Endre =?utf-8?q?Fülöp?= <[email protected]>,
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Endre =?utf-8?q?Fülöp?= <[email protected]>,
Endre =?utf-8?q?Fülöp?= <[email protected]>,
Endre =?utf-8?q?Fülöp?= <[email protected]>,
Endre =?utf-8?q?Fülöp?= <[email protected]>,
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Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/[email protected]>
================
@@ -0,0 +1,76 @@
+.. title:: clang-tidy - performance-expensive-value-or
+
+performance-expensive-value-or
+==============================
+
+Finds calls to ``value_or`` (and alternative spellings ``valueOr``,
+``ValueOr``) on optional types where the return type is expensive to copy.
+These methods return by value, which involves copying the contained value.
+``value()`` and ``operator*`` return references and can be used to avoid the
+copy when appropriate.
+
+The check is applied to types that are not trivially copyable or whose size
+exceeds a configurable threshold. It supports ``std::optional``,
+``boost::optional``, ``absl::optional``, and other optional-like types via
+configuration.
+
+Example:
+
+.. code-block:: c++
+
+ #include <optional>
+ #include <string>
+
+ void consumeRef(const std::string &);
+
+ void example(std::optional<std::string> opt,
+ const std::string &fallback) {
+ // Warning: result binds to const reference, copy is avoidable.
+ const std::string &ref = opt.value_or(fallback);
+
+ // Warning: result passed to const reference parameter.
+ consumeRef(opt.value_or(fallback));
+
+ // Warning: const member called on temporary.
+ auto len = opt.value_or(fallback).size();
+
+ // No warning by default: caller takes ownership.
+ std::string val = opt.value_or("default");
+ }
+
+By default, the check only warns in reference-friendly contexts where the copy
+is clearly avoidable: binding to ``const T&``, passing to a ``const T&``
+parameter, or calling a const member function on the temporary. Contexts where
+the caller takes ownership (binding to a value, passing to a by-value
+parameter) are not flagged unless ``WarnOnOwnershipTaking`` is enabled.
+
+Options
+-------
+
+.. option:: SizeThreshold
+
+ The minimum size in bytes (exclusive) above which a trivially-copyable type
+ is considered expensive to copy. Types with ``sizeof(T) > SizeThreshold``
+ trigger the warning even if they are trivially copyable. Types at or below
+ this threshold only trigger if they are not trivially copyable.
+ Default is `16`.
+
+.. option:: OptionalTypes
+
+ Semicolon-separated list of regular expressions matching fully-qualified
+ names of optional-like class templates to check. The check matches calls to
+ ``value_or`` on specializations of these templates. Default is
+ `::std::optional;::absl::optional;::boost::optional`.
+
+ Example configuration to also check a project-local optional type:
+
+ .. code-block:: yaml
+
+ CheckOptions:
+ performance-expensive-value-or.OptionalTypes:
"::std::optional;::absl::optional;::boost::optional;::myproject::.*Optional"
+
----------------
EugeneZelenko wrote:
```suggestion
```
I don't think that YAML format should be described specifically. General option
description should be enough.
https://github.com/llvm/llvm-project/pull/200166
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