cmStringCommand: clear intermediate matches

When `string(REGEX REPLACE)` or `string(REGEX MATCHALL)` loop
internally, they store their matches, but they do not clear the previous
match from an earlier iteration. This can leave the contents of
`CMAKE_MATCH_<N>` with bogus values for later matches in the string if
they have groups which earlier matched a non-empty string, but now match
an empty string.

Fixes #17079.

1 files changed, 2 insertions, 0 deletions

diff --git a/Source/cmStringCommand.cxx b/Source/cmStringCommand.cxx
index 7a097ba..5a6cf48 100644
--- a/Source/cmStringCommand.cxx
+++ b/Source/cmStringCommand.cxx
@@ -309,6 +309,7 @@ bool cmStringCommand::RegexMatchAll(std::vector<std::string> const& args)
   std::string output;
   const char* p = input.c_str();
   while (re.find(p)) {
+    this->Makefile->ClearMatches();
     this->Makefile->StoreMatches(re);
     std::string::size_type l = re.start();
     std::string::size_type r = re.end();
@@ -391,6 +392,7 @@ bool cmStringCommand::RegexReplace(std::vector<std::string> const& args)
   std::string output;
   std::string::size_type base = 0;
   while (re.find(input.c_str() + base)) {
+    this->Makefile->ClearMatches();
     this->Makefile->StoreMatches(re);
     std::string::size_type l2 = re.start();
     std::string::size_type r = re.end();