[docs] improve documentation for misc-const-correctness

[JonasToth]

Summary

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

[JonasToth]

• mention C limitation

[JonasToth]

@njames93 friendly ping, for https://reviews.llvm.org/D130793 as well :)

clang-tools-extra/docs/clang-tidy/checks/misc/const-correctness.rst

 .. title:: clang-tidy - misc-const-correctness
 
 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``.
 
 .. code-block:: c++
 
   // 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
 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 different ``const`` correctness properties and in general it
-is not possible to find all instantiations of a template. It might be used differently in an
-independent translation unit.
+is not possible to find all instantiations of a template. The template might be used differently 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++
 
   // Declare a variable that will not be modified.
   int constant_value = 42;
 
   // Declare a pointer to that variable, that does not modify either, but misses 'const'.
   // Could be 'const int *pointer_to_constant = &constant_value;'
   int *pointer_to_constant = &constant_value;
 
   // Usage:
   int result = 520 * 120 * (*pointer_to_constant);
 
 This limitation affects the capability to add ``const`` to methods which is not possible, too.
 
 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
   and the value pointing to.
 
   .. 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++
 
     // This variable could still be a constant. But because there is a non-const reference to
     // 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;
-