This patch is generated by a python script that uses regular expressions to
search for string concatenation patterns of the kind
```
std::string str = <ARG0>;
str += <ARG1>;
str += <ARG2>;
...
```
and replaces them with a single `cmStrCat` call
```
std::string str = cmStrCat(<ARG0>, <ARG1>, <ARG2>, ...);
```
If any `<ARGX>` is itself a concatenated string of the kind
```
a + b + c + ...;
```
then `<ARGX>` is split into multiple arguments for the `cmStrCat` call.
If there's a sequence of literals in the `<ARGX>`, then all literals in the
sequence are concatenated and merged into a single literal argument for
the `cmStrCat` call.
Single character strings are converted to single char arguments for
the `cmStrCat` call.
`std::to_string(...)` wrappings are removed from `cmStrCat` arguments,
because it supports numeric types as well as string types.
`arg.substr(x)` arguments to `cmStrCat` are replaced with
`cm::string_view(arg).substr(x)`
In AUTORCC with verbose output write the rcc re-generation reason and
the rcc command as on single string to avoid message chopping in concurrent
builds.
New features
------------
CMake's `AUTOMOC` and `AUTOUIC` now cache information extracted when parsing
source files in `CMakeFiles/<ORIGIN>_autogen.dir/ParseCache.txt`.
This leads to faster `<ORIGIN>_autogen` target rebuilds, because source files
will be parsed again only if they're newer than the `ParseCache.txt` file.
The parse cache will be recomputed if it is older than the CMake executable.
`AUTOMOC` and `AUTOUIC` now check if `moc` or `uic` output files are older
than the `moc` or `uic` executable. If an output file is older than the
compiler, it will be regenerated. Therefore if a new `moc` or `uic` version
is installed, all output files will be regenerated.
`AUTOMOC` and `AUTOUIC` error and warning messages are more detailed.
Internal changes
----------------
`moc` and `uic` output file names are not computed in the `_autogen`
target anymore but in `cmQtAutoGenInitializer`. This makes the available at
the configuration stage for improved dependency computations (to be done).
In `AutogenInfo.cmake`, equally sized lists for "source file names",
"source file flags" and "compiler output file names" are passed to the
`_autogen` target. This replaces the separate file lists for
`AUTOMOC` and `AUTOUIC`.
Files times are read from the file system only once by using `cmFileTime`
instances instead of `cmQtAutoGenerator::FileSystem::FileIsOlderThan` calls.
All calls to not thread safe file system functions are moved to non concurrent
fence jobs (see `cmWorkerPool::JobT::IsFence()`). This renders the
`cmQtAutoGenerator::FileSystem` wrapper class obsolete and it is removed.
Instead of composing a single large settings string that is fed to the
`cmCryptoHash`, now all setting sub strings are fed one by one to the
`cmCryptoHash` and the finalized result is stored.
The `std::mutex` in `cmQtAutoGenerator::Logger` is tagged `mutable` and most
`cmQtAutoGenerator::Logger` methods become `const`.
Outlook
-------
This patch provides the framework required to
- extract dependencies from `.ui` files in `AUTOUIC`.
These will help to address issue
#15420 "AUTOUIC: Track uic external inputs".
- generate adaptive `make` and `ninja` files in the `_autogen` target.
These will help to address issue
#16776 "AUTOUIC: Ninja needs two passes to correctly build Qt project".
- generate (possibly empty) `moc` and `uic` files for all headers instead of a
`mocs_compilation.cpp` file.
This will help to address issue
#17277 "AUTOMOC: Provide a option to allow AUTOMOC to compile individual "
"moc_x.cxx instead of including all in mocs_compilation.cxx"
