Most `const char*` arguments converted to `const std::string&`
in `cmDepends` and derived classes.
In addition performed minor code cleanup.

Nothing ever set `CompileDirectory` except `SetDirectory()`, but
nothing ever called that function. Therefore, `CompileDirectory`
was always empty for the attempt to change directory in `Check()`,
which therefore would always fail. Nothing was checking the result
and the code was always going to have no effect.

Changes done via `clang-tidy` with some manual fine-tuning
for the variable naming and `auto` type deduction
where appropriate.

Automate with:

git grep -l '#include <cm_' -- Source \
  | xargs sed -i 's/#include <\(cm_.*\)>/#include "\1"/g'

git grep -l '#include <cmsys/' -- Source \
  | xargs sed -i 's/#include <\(cmsys\/.*\)>/#include "\1"/g'

git grep -l '#include <cm[A-Z]' -- Source \
  | xargs sed -i 's/#include <\(cm[A-Z].*\)>/#include "\1"/g'

These functions just need to change the directory for a block of code
and then go back to the caller's expected location. Use
cmWorkingDirectory to ensure that all return paths are handled.

Per-source copyright/license notice headers that spell out copyright holder
names and years are hard to maintain and often out-of-date or plain wrong.
Precise contributor information is already maintained automatically by the
version control tool.  Ultimately it is the receiver of a file who is
responsible for determining its licensing status, and per-source notices are
merely a convenience.  Therefore it is simpler and more accurate for
each source to have a generic notice of the license name and references to
more detailed information on copyright holders and full license terms.

Our `Copyright.txt` file now contains a list of Contributors whose names
appeared source-level copyright notices.  It also references version control
history for more precise information.  Therefore we no longer need to spell
out the list of Contributors in each source file notice.

Replace CMake per-source copyright/license notice headers with a short
description of the license and links to `Copyright.txt` and online information
available from "https://cmake.org/licensing".  The online URL also handles
cases of modules being copied out of our source into other projects, so we
can drop our notices about replacing links with full license text.

Run the `Utilities/Scripts/filter-notices.bash` script to perform the majority
of the replacements mechanically.  Manually fix up shebang lines and trailing
newlines in a few files.  Manually update the notices in a few files that the
script does not handle.

Run the `Utilities/Scripts/clang-format.bash` script to update
all our C++ code to a new style defined by `.clang-format`.
Use `clang-format` version 3.8.

* If you reached this commit for a line in `git blame`, re-run the blame
  operation starting at the parent of this commit to see older history
  for the content.

* See the parent commit for instructions to rebase a change across this
  style transition commit.

Modern editors provide plenty of ways to visually separate functions.
Drop the explicit comments that previously served this purpose.
Use the following command to automate the change:

    $ git ls-files -z -- \
        "*.c" "*.cc" "*.cpp" "*.cxx" "*.h" "*.hh" "*.hpp" "*.hxx" |
      egrep -z -v "^Source/cmCommandArgumentLexer\." |
      egrep -z -v "^Source/cmCommandArgumentParser(\.y|\.cxx|Tokens\.h)" |
      egrep -z -v "^Source/cmDependsJavaLexer\." |
      egrep -z -v "^Source/cmDependsJavaParser(\.y|\.cxx|Tokens\.h)" |
      egrep -z -v "^Source/cmExprLexer\." |
      egrep -z -v "^Source/cmExprParser(\.y|\.cxx|Tokens\.h)" |
      egrep -z -v "^Source/cmFortranLexer\." |
      egrep -z -v "^Source/cmFortranParser(\.y|\.cxx|Tokens\.h)" |
      egrep -z -v "^Source/cmListFileLexer\." |
      egrep -z -v "^Source/cm_sha2" |
      egrep -z -v "^Source/(kwsys|CursesDialog/form)/" |
      egrep -z -v "^Utilities/(KW|cm).*/" |
      xargs -0 sed -i '/^\(\/\/---*\|\/\*---*\*\/\)$/ {d;}'

This avoids modifying third-party sources and generated sources.

Sort include directives within each block (separated by a blank line) in
lexicographic order (except to prioritize `sys/types.h` first).  First
run `clang-format` with the config file:

    ---
    SortIncludes: false
    ...

Commit the result temporarily.  Then run `clang-format` again with:

    ---
    SortIncludes: true
    IncludeCategories:
      - Regex:    'sys/types.h'
        Priority: -1
    ...

Commit the result temporarily.  Start a new branch and cherry-pick the
second commit.  Manually resolve conflicts to preserve indentation of
re-ordered includes.  This cleans up the include ordering without
changing any other style.

Use the following command to run `clang-format`:

    $ git ls-files -z -- \
        '*.c' '*.cc' '*.cpp' '*.cxx' '*.h' '*.hh' '*.hpp' '*.hxx' |
      egrep -z -v '(Lexer|Parser|ParserHelper)\.' |
      egrep -z -v '^Source/cm_sha2' |
      egrep -z -v '^Source/(kwsys|CursesDialog/form)/' |
      egrep -z -v '^Utilities/(KW|cm).*/' |
      egrep -z -v '^Tests/Module/GenerateExportHeader' |
      egrep -z -v '^Tests/RunCMake/CommandLine/cmake_depends/test_UTF-16LE.h' |
      xargs -0 clang-format -i

This selects source files that do not come from a third-party.
Inspired-by: Daniel Pfeifer <daniel@pfeifer-mail.de>

All compilers hosting CMake support the std class.

Replacements were detected and performed by the clang tool
remove-cstr-calls on a linux build.

Delay conversion of the path to object files (on the left-hand side
of dependencies) until just before they are written.  Also do not
convert the format of paths written to the 'depend.internal' file.
This is consistent with the way the right-hand side of dependencies
are already handled.

Rename the internal enumeration value for converting paths destined
for use in Makefile rule syntax.

Use the clang RemoveCStrCalls tool to automatically migrate the
code. This was only run on linux, so does not have any positive or
negative effect on other platforms.

Also use SystemTools::Fopen() instead of fopen().
This is to eventually support utf-8 filenames.

Some dependency-generators (such as cmDependsFortran) generate multiple
entries per depender, so erasing the dependency vector for each depender
found loses earlier dependencies.
Signed-off-by: Michael Wild <themiwi@users.sourceforge.net>

This patch is heavily inspired by Michael Wild.

The interfaces cmDepends::Write and cmDepends::WriteDependencies where
extended to allow multiple dependees (sources) per depender (object).
cmDepends::Write first collect all dependencies into a std::set before
passing it to cmDepends::WriteDependencies.

cmDependsC::WriteDependencies also first collects all explicit and
implicit dependencies into a std::set and only then writes
depend.{internal,make}. The implementation of cmDependsFortran simply
loops over all sources and proceeds as before, whereas the cmDependsJava
implementation is as trivial as before.

This is for preventing exponential growth of depend.{internal,make} in
the next commit which fixes dependency-vector erasure in
cmDepends::CheckDependencies.
Inspired-by: Michael Wild <themiwi@users.sourceforge.net>

Alex

If the depender (e.g. foo.o) does not exist, also rescan dependencies if
one of the dependees (e.g. foo.cxx) is older than the already existing
depend.internal file, since this means it can be out of date.

Alex

Our Git commit hooks disallow modification or addition of lines with
trailing whitespace.  Wipe out all remnants of trailing whitespace
everywhere except third-party code.

Run the following shell code:

git ls-files -z -- \
 bootstrap doxygen.config '*.readme' \
 '*.c' '*.cmake' '*.cpp' '*.cxx' \
 '*.el' '*.f' '*.f90' '*.h' '*.in' '*.in.l' '*.java' \
 '*.mm' '*.pike' '*.py' '*.txt' '*.vim' |
egrep -z -v '^(Utilities/cm|Source/(kwsys|CursesDialog/form)/)' |
egrep -z -v '^(Modules/CPack\..*\.in)' |
xargs -0 sed -i 's/ \+$//'

Avoid assignment inside the if.

Declare variable only once at a scope appropriate for both uses.

Eliminate callers of cmMakefile::GetIncludeDirectories.

All callers of GetIncludeDirectories should go through the local generator
object.

Only the local generator calls cmTarget::GetIncludeDirectories directly.

The KWSys SystemTools::GetMaximumFilePathLength method is poorly
conceived and should not be used.  The cmDepends code honors its own
MaxPath buffer size.  Just hard-code it.

This converts the CMake license to a pure 3-clause OSI-approved BSD
License.  We drop the previous license clause requiring modified
versions to be plainly marked.  We also update the CMake copyright to
cover the full development time range.

Now only the dependencies for the file where the dependencies actually may
have changed are rescanned, before that this was done for all source files
even if only one source file had changed.
This reduces e.g. on my machine the time for scanning the dependencies
of kdelibs/khtml/ when only one file (khtml_global.cpp) has changed from
around 7.5 seconds to 1.2 seconds.

The tests succeed, it does what I expected it to do on kdelibs, and Brad
also reviewed the patch, so I think it should be ok.

Alex

When reading the depend.internal file, check only once for every depender
whether it exists, instead of repeatedly in a loop for each dependee. Within
that function it can only change of the depender is removed. This is taken
care of.
This reduces the number of access() calls in kdelibs/khtml from 180000 to
90000 (i.e. 50%), and reduces the time for that (without the actual
scanning) from 0.3 s to 0.21 s on my system.

Alex

  - Move lookup of config variables from cmLocalUnixMakefileGenerator3 to cmDepends hierarchy.

  - See issue #5809
  - Keep information about all sources in the target until deps are written
  - Create a fortran.internal file after scanning that lists modules provided
  - Load fortran.internal files from linked targets to find modules
  - Search the include path for external modules
  - Create file-level deps on in-project module timestamps or external mods