Add some static casts to make explicit some sign conversions in order to
avoid warnings about the same. This is by no means an attempt to fix all
such warnings, but these instances were especially egregious as they
would be raised across many source files.
Also change a post-increment of an iterator to pre-increment. At worst,
this does nothing, but pre-increment is potentially more efficient.
`include-what-you-use` diagnostics, in practice, are specific to
the environment's compiler and standard library. Update includes
to satisfy IWYU for our CI job under Debian 12.
#pragma once is a widely supported compiler pragma, even though it is
not part of the C++ standard. Many of the issues keeping #pragma once
from being standardized (distributed filesystems, build farms, hard
links, etc.) do not apply to CMake - it is easy to build CMake on a
single machine. CMake also does not install any header files which can
be consumed by other projects (though cmCPluginAPI.h has been
deliberately omitted from this conversion in case anyone is still using
it.) Finally, #pragma once has been required to build CMake since at
least August 2017 (7f29bbe6 enabled server mode unconditionally, which
had been using #pragma once since September 2016 (b13d3e0d)). The fact
that we now require C++11 filters out old compilers, and it is unlikely
that there is a compiler which supports C++11 but does not support
#pragma once.
Provide a standardized way to handle the C++ "standard" headers
customized to be used with current CMake C++ standard constraints.
Offer under directory `cm` headers which can be used as direct
replacements of the standard ones. For example:
#include <cm/string_view>
can be used safely for CMake development in place of the `<string_view>`
standard header.
Fixes: #19491
The `str()` method must be non-const because it may need to internally
mutate the representation of the string in order to have an owned
`std::string` instance holding the exact string (not a superstring).
This is inconvenient in contexts where we can ensure that no mutation
is needed to get a `std::string const&`.
Add a `str_if_stable() const` method that returns `std::string const*`
so we can return `nullptr` if if mutation would be necessary to get a
`std::string const&`. Add supporting `is_stable() const` and
`stabilize()` methods to check and enforce stable availability of
`std::string const&`. These can be used to create `String const`
instances from which we can still get a `std::string const&` via
`*str_if_stable()` by maintaining the stability invariant at runtime.
This will allow creation of `cm::String` instances that borrow from
non-owned storage. It is the caller's responsibility to ensure that
no copy of the instance outlives the borrowed buffer.
Create a `cm::String` type that holds a view of a string buffer and
optionally shares ownership of the buffer. Instances can either
borrow longer-lived storage (e.g. static storage of string literals)
or internally own a `std::string` instance. In the latter case,
share ownership with copies and substrings. Allocate a new internal
string only on operations that require mutation.
This will allow us to recover string sharing semantics that we
used to get from C++98 std::string copy-on-write implementations.
Such implementations are not allowed by C++11 so code our own in
a custom string type instead.
