[clang-tools-extra] b5b7503 - [docs] improve documentation for misc-const-correctness
Jonas Toth via cfe-commits
cfe-commits at lists.llvm.org
Mon Aug 29 02:21:20 PDT 2022
Author: Jonas Toth
Date: 2022-08-29T11:20:47+02:00
New Revision: b5b750346346bfe95c7c6b1cceacc6cfccc8f4f4
URL: https://github.com/llvm/llvm-project/commit/b5b750346346bfe95c7c6b1cceacc6cfccc8f4f4
DIFF: https://github.com/llvm/llvm-project/commit/b5b750346346bfe95c7c6b1cceacc6cfccc8f4f4.diff
LOG: [docs] improve documentation for misc-const-correctness
Improve the documentation for 'misc-const-correctness' to:
- include better examples
- improve the english
- fix links to other checks that were broken due to the directory-layout changes
- mention the limitation that the check does not run on `C` code.
Addresses #56749, #56958
Reviewed By: njames93
Differential Revision: https://reviews.llvm.org/D132244
Added:
Modified:
clang-tools-extra/docs/clang-tidy/checks/misc/const-correctness.rst
Removed:
################################################################################
diff --git a/clang-tools-extra/docs/clang-tidy/checks/misc/const-correctness.rst b/clang-tools-extra/docs/clang-tidy/checks/misc/const-correctness.rst
index 76d283da37dd1..cc6ae33a414d2 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/misc/const-correctness.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/misc/const-correctness.rst
@@ -4,12 +4,12 @@ misc-const-correctness
======================
This check implements detection of local variables which could be declared as
-``const``, but are not. Declaring variables as ``const`` is required or recommended by many
+``const`` but are not. Declaring variables as ``const`` is required or recommended by many
coding guidelines, such as:
`CppCoreGuidelines ES.25 <https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es25-declare-an-object-const-or-constexpr-unless-you-want-to-modify-its-value-later-on>`_
and `AUTOSAR C++14 Rule A7-1-1 (6.7.1 Specifiers) <https://www.autosar.org/fileadmin/user_upload/standards/adaptive/17-03/AUTOSAR_RS_CPP14Guidelines.pdf>`_.
-Please note that this analysis is type-based only. Variables that are not modified
+Please note that this check's analysis is type-based only. Variables that are not modified
but used to create a non-const handle that might escape the scope are not diagnosed
as potential ``const``.
@@ -18,25 +18,29 @@ as potential ``const``.
// Declare a variable, which is not ``const`` ...
int i = 42;
// but use it as read-only. This means that `i` can be declared ``const``.
- int result = i * i;
+ int result = i * i; // Before transformation
+ int const result = i * i; // After transformation
-The check can analyzes values, pointers and references but not (yet) pointees:
+The check can analyze values, pointers and references but not (yet) pointees:
.. code-block:: c++
// Normal values like built-ins or objects.
- int potential_const_int = 42; // 'const int potential_const_int = 42' suggestion.
+ int potential_const_int = 42; // Before transformation
+ int const potential_const_int = 42; // After transformation
int copy_of_value = potential_const_int;
- MyClass could_be_const; // 'const MyClass could_be_const' suggestion;
+ MyClass could_be_const; // Before transformation
+ MyClass const could_be_const; // After transformation
could_be_const.const_qualified_method();
// References can be declared const as well.
- int &reference_value = potential_const_int; // 'const int &reference_value' suggestion.
+ int &reference_value = potential_const_int; // Before transformation
+ int const& reference_value = potential_const_int; // After transformation
int another_copy = reference_value;
// The similar semantics of pointers are not (yet) analyzed.
- int *pointer_variable = &potential_const_int; // Not 'const int *pointer_variable' suggestion.
+ int *pointer_variable = &potential_const_int; // _NO_ 'const int *pointer_variable' suggestion.
int last_copy = *pointer_variable;
The automatic code transformation is only applied to variables that are declared in single
@@ -44,18 +48,20 @@ declarations. You may want to prepare your code base with
`readability-isolate-declaration <../readability/isolate-declaration.html>`_ first.
Note that there is the check
-`cppcoreguidelines-avoid-non-const-global-variables <cppcoreguidelines-avoid-non-const-global-variables.html>`_
+`cppcoreguidelines-avoid-non-const-global-variables <../cppcoreguidelines/avoid-non-const-global-variables.html>`_
to enforce ``const`` correctness on all globals.
Known Limitations
-----------------
+The check does not run on `C` code.
+
The check will not analyze templated variables or variables that are instantiation dependent.
Different instantiations can result in
diff erent ``const`` correctness properties and in general it
-is not possible to find all instantiations of a template. It might be used
diff erently in an
-independent translation unit.
+is not possible to find all instantiations of a template. The template might be used
diff erently in
+an independent translation unit.
-Pointees can not be analyzed for constness yet. The following code is shows this limitation.
+Pointees can not be analyzed for constness yet. The following code shows this limitation.
.. code-block:: c++
@@ -74,15 +80,35 @@ This limitation affects the capability to add ``const`` to methods which is not
Options
-------
-.. option:: AnalyzeValues (default = 1)
+.. option:: AnalyzeValues (default = true)
Enable or disable the analysis of ordinary value variables, like ``int i = 42;``
-.. option:: AnalyzeReferences (default = 1)
+ .. code-block:: c++
+
+ // Warning
+ int i = 42;
+ // No warning
+ int const i = 42;
+
+ // Warning
+ int a[] = {42, 42, 42};
+ // No warning
+ int const a[] = {42, 42, 42};
+
+.. option:: AnalyzeReferences (default = true)
Enable or disable the analysis of reference variables, like ``int &ref = i;``
-.. option:: WarnPointersAsValues (default = 0)
+ .. code-block:: c++
+
+ int i = 42;
+ // Warning
+ int& ref = i;
+ // No warning
+ int const& ref = i;
+
+.. option:: WarnPointersAsValues (default = false)
This option enables the suggestion for ``const`` of the pointer itself.
Pointer values have two possibilities to be ``const``, the pointer
@@ -90,28 +116,36 @@ Options
.. code-block:: c++
- const int value = 42;
- const int * const pointer_variable = &value;
+ int value = 42;
- // The following operations are forbidden for `pointer_variable`.
- // *pointer_variable = 44;
- // pointer_variable = nullptr;
+ // Warning
+ const int * pointer_variable = &value;
+ // No warning
+ const int *const pointer_variable = &value;
-.. option:: TransformValues (default = 1)
+.. option:: TransformValues (default = true)
- Provides fixit-hints for value types that automatically adds ``const`` if its a single declaration.
+ Provides fixit-hints for value types that automatically add ``const`` if its a single declaration.
.. code-block:: c++
- // Emits a hint for 'value' to become 'const int value = 42;'.
+ // Before
int value = 42;
+ // After
+ int const value = 42;
+
+ // Before
+ int a[] = {42, 42, 42};
+ // After
+ int const a[] = {42, 42, 42};
+
// Result is modified later in its life-time. No diagnostic and fixit hint will be emitted.
int result = value * 3;
result -= 10;
-.. option:: TransformReferences (default = 1)
+.. option:: TransformReferences (default = true)
- Provides fixit-hints for reference types that automatically adds ``const`` if its a single
+ Provides fixit-hints for reference types that automatically add ``const`` if its a single
declaration.
.. code-block:: c++
@@ -120,31 +154,45 @@ Options
// it, it can not be transformed (yet).
int value = 42;
// The reference 'ref_value' is not modified and can be made 'const int &ref_value = value;'
+ // Before
int &ref_value = value;
+ // After
+ int const &ref_value = value;
// Result is modified later in its life-time. No diagnostic and fixit hint will be emitted.
int result = ref_value * 3;
result -= 10;
-.. option:: TransformPointersAsValues (default = 0)
+.. option:: TransformPointersAsValues (default = false)
Provides fixit-hints for pointers if their pointee is not changed. This does not analyze if the
value-pointed-to is unchanged!
- Requires 'WarnPointersAsValues' to be 1.
+ Requires 'WarnPointersAsValues' to be 'true'.
.. code-block:: c++
int value = 42;
- // Emits a hint that 'ptr_value' may become 'int *const ptr_value = &value' because its pointee
- // is not changed.
+
+ // Before
+ const int * pointer_variable = &value;
+ // After
+ const int *const pointer_variable = &value;
+
+ // Before
+ const int * a[] = {&value, &value};
+ // After
+ const int *const a[] = {&value, &value};
+
+ // Before
int *ptr_value = &value;
+ // After
+ int *const ptr_value = &value;
- int result = 100 * (*ptr_value);
- // This modification of the pointee is still allowed and not analyzed/diagnosed.
+ int result = 100 * (*ptr_value); // Does not modify the pointer itself.
+ // This modification of the pointee is still allowed and not diagnosed.
*ptr_value = 0;
// The following pointer may not become a 'int *const'.
int *changing_pointee = &value;
changing_pointee = &result;
-
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