Backport: Updated the code and comment for running a regex over multiple lines at once

instead of breaking up into lines.
Using the preprocessor to hide the multiline code instead of comments so that it
is easier to experiment with.

Backport of changeset 7028:9227461c9330.

1 files changed, 14 insertions, 8 deletions

diff --git a/src/Document.cxx b/src/Document.cxx
index b7dc4c8d1..c98118986 100644
--- a/src/Document.cxx
+++ b/src/Document.cxx
@@ -2963,14 +2963,19 @@ bool MatchOnLines(const Document *doc, const Regex &regexp, const RESearchRange
 	bool matched = false;
 	std::match_results<Iterator> match;
 
-	// MSVC and libc++ have problems with ^ and $ matching line ends inside a range
-	// If they didn't then the line by line iteration could be removed for the forwards
-	// case and replaced with the following 4 lines:
-	//	Iterator uiStart(doc, startPos);
-	//	Iterator uiEnd(doc, endPos);
-	//	flagsMatch = MatchFlags(doc, startPos, endPos);
-	//	matched = std::regex_search(uiStart, uiEnd, match, regexp, flagsMatch);
-
+	// MSVC and libc++ have problems with ^ and $ matching line ends inside a range.
+	// CRLF line ends are also a problem as ^ and $ only treat LF as a line end.
+	// The std::regex::multiline option was added to C++17 to improve behaviour but
+	// has not been implemented by compiler runtimes with MSVC always in multiline
+	// mode and libc++ and libstdc++ always in single-line mode.
+	// If multiline regex worked well then the line by line iteration could be removed
+	// for the forwards case and replaced with the following 4 lines:
+#ifdef REGEX_MULTILINE
+	Iterator itStart(doc, resr.startPos);
+	Iterator itEnd(doc, resr.endPos);
+	const std::regex_constants::match_flag_type flagsMatch = MatchFlags(doc, resr.startPos, resr.endPos);
+	matched = std::regex_search(itStart, itEnd, match, regexp, flagsMatch);
+#else
 	// Line by line.
 	for (Sci::Line line = resr.lineRangeStart; line != resr.lineRangeBreak; line += resr.increment) {
 		const Range lineRange = resr.LineRange(line);
@@ -2999,6 +3004,7 @@ bool MatchOnLines(const Document *doc, const Regex &regexp, const RESearchRange
 			break;
 		}
 	}
+#endif
 	if (matched) {
 		for (size_t co = 0; co < match.size(); co++) {
 			search.bopat[co] = match[co].first.Pos();