file: Sort GLOB results to make it deterministic (#14491)

Even though the `file(GLOB)` documentation specifically warns against
using it to collect a list of source files, projects often do it anyway.
Since it uses `readdir()`, the list of files will be unsorted.
This list is often passed directly to add_executable / add_library.
Linking binaries with an unsorted list will make it unreproducible,
which means that the produced binary will differ depending on the
unpredictable `readdir()` order.

To solve those reproducibility issues in a lot of programs (which don't
explicitly `list(SORT)` the list manually), sort the resulting list of
the `file(GLOB)` command.

A more detailed rationale about reproducible builds is available
[here](https://reproducible-builds.org/).

1 files changed, 1 insertions, 0 deletions

diff --git a/Source/cmFileCommand.cxx b/Source/cmFileCommand.cxx
index 5363a992f0..4e72f36138 100644
--- a/Source/cmFileCommand.cxx
+++ b/Source/cmFileCommand.cxx
@@ -823,6 +823,7 @@ bool cmFileCommand::HandleGlobCommand(std::vector<std::string> const& args,
 
     std::vector<std::string>::size_type cc;
     std::vector<std::string>& files = g.GetFiles();
+    std::sort(files.begin(), files.end());
     for (cc = 0; cc < files.size(); cc++) {
       if (!first) {
         output += ";";