From af775c5b2274a4cb0b465b4f6fae531a68db8890 Mon Sep 17 00:00:00 2001
From: Alex Alabuzhev <alabuzhev@gmail.com>
Date: Mon, 2 Dec 2024 20:42:42 +0000
Subject: [PATCH] Use DECRQM 2027 to check grapheme clusters state (thanks to
 DHowett)

---
 far/changelog      |  5 ++++
 far/char_width.cpp | 17 +++++++++--
 far/console.cpp    | 71 ++++++++++++++++++++++++++++++++++++----------
 far/console.hpp    |  4 +++
 far/vbuild.m4      |  2 +-
 5 files changed, 81 insertions(+), 18 deletions(-)

diff --git a/far/changelog b/far/changelog
index 48e538628c..9d16993c5e 100644
--- a/far/changelog
+++ b/far/changelog
@@ -1,3 +1,8 @@
+--------------------------------------------------------------------------------
+drkns 2024-12-02 20:39:53+00:00 - build 6398
+
+1. Use DECRQM 2027 to check grapheme clusters state (thanks to DHowett).
+
 --------------------------------------------------------------------------------
 drkns 2024-12-01 23:24:48+00:00 - build 6397
 
diff --git a/far/char_width.cpp b/far/char_width.cpp
index 52011215da..6b0e0006ed 100644
--- a/far/char_width.cpp
+++ b/far/char_width.cpp
@@ -39,6 +39,7 @@ THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 // Internal:
 #include "console.hpp"
 #include "locale.hpp"
+#include "log.hpp"
 
 // Platform:
 
@@ -555,7 +556,19 @@ namespace char_width
 
 	bool is_grapheme_clusters_on()
 	{
-		static const auto Result = console.GetWidthPreciseExpensive(L"à"sv);
-		return Result == 1;
+		static const auto Result = []
+		{
+			if (const auto IsOn = console.is_grapheme_clusters_on(); IsOn)
+			{
+				LOGDEBUG(L"Grapheme clusters (VT): {}"sv, *IsOn);
+				return *IsOn;
+			}
+
+			const auto IsOn = console.GetWidthPreciseExpensive(L"à"sv) == 1;
+			LOGDEBUG(L"Grapheme clusters (heuristics): {}"sv, IsOn);
+			return IsOn;
+		}();
+
+		return Result;
 	}
 }
diff --git a/far/console.cpp b/far/console.cpp
index 30c7aabbac..e95d369788 100644
--- a/far/console.cpp
+++ b/far/console.cpp
@@ -631,15 +631,15 @@ namespace console_detail
 
 		std::optional<size_t>
 			FirstTokenPrefixPos,
-			FirstTokenSuffixPos,
-			SecondTokenPrefixPos,
-			SecondTokenSuffixPos;
+			FirstTokenSuffixPos;
 
 		const auto
 			TokenPrefix = CSI "?"sv,
 			TokenSuffix = L"c"sv;
 
-		while (!SecondTokenSuffixPos)
+		size_t DA_ResponseSize{};
+
+		for (;;)
 		{
 			wchar_t ResponseBuffer[8192];
 			size_t ResponseSize;
@@ -655,21 +655,19 @@ namespace console_detail
 
 			if (FirstTokenPrefixPos && !FirstTokenSuffixPos)
 				if (const auto Pos = Response.find(TokenSuffix, *FirstTokenPrefixPos + TokenPrefix.size()); Pos != Response.npos)
+				{
 					FirstTokenSuffixPos = Pos;
+					DA_ResponseSize = Pos + TokenSuffix.size();
+				}
 
-			if (FirstTokenSuffixPos && !SecondTokenPrefixPos)
-				if (const auto Pos = Response.find(TokenPrefix, *FirstTokenSuffixPos + TokenSuffix.size()); Pos != Response.npos)
-					SecondTokenPrefixPos = Pos;
-
-			if (SecondTokenPrefixPos && !SecondTokenSuffixPos)
-				if (const auto Pos = Response.find(TokenSuffix, *SecondTokenPrefixPos + TokenPrefix.size()); Pos != Response.npos)
-					SecondTokenSuffixPos = Pos;
+			if (DA_ResponseSize && Response.size() >= DA_ResponseSize * 2)
+			{
+				if (const auto DA_Response = string_view(Response).substr(*FirstTokenPrefixPos, DA_ResponseSize); Response.ends_with(DA_Response))
+					break;
+			}
 		}
 
-		Response.resize(*SecondTokenPrefixPos);
-		Response.erase(0, *FirstTokenSuffixPos + TokenSuffix.size());
-
-		return Response;
+		return Response.substr(DA_ResponseSize, Response.size() - DA_ResponseSize * 2);
 	}
 
 	console::console():
@@ -3100,6 +3098,49 @@ namespace console_detail
 		send_vt_command(far::format(OSC("9001;CmdNotFound;{}"), Command));
 	}
 
+	std::optional<bool> console::is_grapheme_clusters_on() const
+	{
+		try
+		{
+#define DECRQM_REQUEST "?2027"
+
+			const auto ResponseData = query_vt(CSI DECRQM_REQUEST "$p"sv);
+			if (ResponseData.empty())
+			{
+				LOGWARNING(L"DECRQM 2027 query is not supported"sv);
+				return {};
+			}
+
+			const auto
+				Prefix = CSI DECRQM_REQUEST ";"sv,
+				Suffix = L"$y"sv;
+
+#undef DECRQM_REQUEST
+
+			const auto give_up = [&]
+			{
+				throw far_exception(far::format(L"Incorrect response: {}"sv, ResponseData), false);
+			};
+
+			if (ResponseData.size() != Prefix.size() + 1 + Suffix.size() || !ResponseData.starts_with(Prefix) || !ResponseData.ends_with(Suffix))
+				give_up();
+
+			switch (ResponseData[Prefix.size()])
+			{
+			case L'3': return true;
+			case L'4': return false;
+			default:
+				give_up();
+				std::unreachable();
+			}
+		}
+		catch (far_exception const& e)
+		{
+			LOGERROR(L"{}"sv, e);
+			return {};
+		}
+	}
+
 	bool console::GetCursorRealPosition(point& Position) const
 	{
 		CONSOLE_SCREEN_BUFFER_INFO ConsoleScreenBufferInfo;
diff --git a/far/console.hpp b/far/console.hpp
index 76efff8a76..1482e04027 100644
--- a/far/console.hpp
+++ b/far/console.hpp
@@ -191,6 +191,7 @@ namespace console_detail
 
 		[[nodiscard]]
 		size_t GetWidthPreciseExpensive(string_view Str);
+		[[nodiscard]]
 		size_t GetWidthPreciseExpensive(char32_t Codepoint);
 		void ClearWideCache();
 
@@ -213,6 +214,9 @@ namespace console_detail
 		void command_finished(int ExitCode) const;
 		void command_not_found(string_view Command) const;
 
+		[[nodiscard]]
+		std::optional<bool> is_grapheme_clusters_on() const;
+
 		[[nodiscard]]
 		short GetDelta() const;
 
diff --git a/far/vbuild.m4 b/far/vbuild.m4
index 495c1df87c..602f247530 100644
--- a/far/vbuild.m4
+++ b/far/vbuild.m4
@@ -1 +1 @@
-6397
+6398