Terminal loop, virtual buffers, yank bound

- kte refuses to start when stdin is not a terminal: piped bytes were
  executed as editor commands (C-k s plus a path writes a file), and
  after EOF the loop spun at full CPU with no way to quit.
- The terminal frontend handles all pending input before drawing (a
  paste used to cost a frame and a full redraw per character) and
  redraws only after input, a resize or deferred opens, else once a
  second. The renderer caches, per row and buffer version, where the
  horizontally scrolled part of a line starts and the cursor's render
  column, instead of rescanning the line every frame. Idle CPU with the
  cursor at the end of a 20 MB line: one full core -> ~1%.
- Buffers with a virtual name (+HELP+) are not journaled and saving one
  asks for a file name; it used to write ./+HELP+ and journal under
  that path.
- Yank with a repeat count is capped at 256 MiB in total instead of
  reserving count x size bytes (C-u 1000000 C-y of a large kill).
- Remove an overload clang reports as unused (-Werror on macOS).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015rcVQiiWyTzoNrsvLSaAfB

Buffer.cc

@@ -322,6 +322,7 @@ Buffer::Buffer(const Buffer &other)
 	rows_cache_dirty_ = other.rows_cache_dirty_;
 	filename_         = other.filename_;
 	is_file_backed_   = other.is_file_backed_;
+	is_virtual_       = other.is_virtual_;
 	dirty_            = other.dirty_;
 	read_only_        = other.read_only_;
 	mark_set_         = other.mark_set_;
@@ -375,6 +376,7 @@ Buffer::operator=(const Buffer &other)
 	rows_cache_dirty_ = other.rows_cache_dirty_;
 	filename_         = other.filename_;
 	is_file_backed_   = other.is_file_backed_;
+	is_virtual_       = other.is_virtual_;
 	dirty_            = other.dirty_;
 	read_only_        = other.read_only_;
 	mark_set_         = other.mark_set_;
@@ -420,6 +422,7 @@ Buffer::Buffer(Buffer &&other) noexcept
 	  rows_(std::move(other.rows_)),
 	  filename_(std::move(other.filename_)),
 	  is_file_backed_(other.is_file_backed_),
+	  is_virtual_(other.is_virtual_),
 	  dirty_(other.dirty_),
 	  read_only_(other.read_only_),
 	  mark_set_(other.mark_set_),
@@ -470,6 +473,7 @@ Buffer::operator=(Buffer &&other) noexcept
 	rows_                 = std::move(other.rows_);
 	filename_             = std::move(other.filename_);
 	is_file_backed_       = other.is_file_backed_;
+	is_virtual_           = other.is_virtual_;
 	dirty_                = other.dirty_;
 	read_only_            = other.read_only_;
 	mark_set_             = other.mark_set_;
@@ -548,6 +552,7 @@ Buffer::OpenFromFile(const std::string &path, std::string &err)
 		nrows_          = 0;
 		filename_       = norm;
 		is_file_backed_ = false;
+		is_virtual_     = false;
 		dirty_          = false;
 
 		// Reset cursor/viewport state
@@ -620,6 +625,7 @@ Buffer::OpenFromFile(const std::string &path, std::string &err)
 	nrows_            = 0; // not used under PieceTable
 	filename_         = norm;
 	is_file_backed_   = true;
+	is_virtual_       = false;
 	dirty_            = false;
 	RefreshOnDiskIdentity();
 
@@ -702,6 +708,7 @@ Buffer::SaveAs(const std::string &path, std::string &err)
 
 	filename_       = out_path;
 	is_file_backed_ = true;
+	is_virtual_     = false;
 	dirty_          = false;
 	RefreshOnDiskIdentity();
 	return true;

Buffer.h

@@ -334,6 +334,7 @@ public:
 	{
 		filename_       = name;
 		is_file_backed_ = false;
+		is_virtual_     = true;
 	}
 
 
@@ -343,6 +344,14 @@ public:
 	}
 
 
+	// A virtual buffer (e.g. "+HELP+") has a display name that is not a path:
+	// it is never journaled, and saving it asks for a file name.
+	[[nodiscard]] bool IsVirtual() const
+	{
+		return is_virtual_;
+	}
+
+
 	[[nodiscard]] bool Dirty() const
 	{
 		return dirty_;
@@ -677,6 +686,7 @@ private:
 
 	std::string filename_;
 	bool is_file_backed_              = false;
+	bool is_virtual_                  = false;
 	bool dirty_                       = false;
 	bool read_only_                   = false;
 	bool mark_set_                    = false;

Command.cc

@@ -108,13 +108,6 @@ utf8_next_len(std::string_view line, std::size_t x)
 }
 
 
-static inline std::string_view
-line_view(const Buffer::Line &l)
-{
-	return std::string_view(l.Data(), l.Size());
-}
-
-
 static inline std::string_view
 line_view(const std::string &l)
 {
@@ -937,7 +930,8 @@ cmd_save(CommandContext &ctx)
 	// Allow saving directly to a filename if buffer was opened with a
 	// non-existent path (not yet file-backed but has a filename).
 	if (!buf->IsFileBacked()) {
-		if (!buf->Filename().empty()) {
+		// A virtual buffer's name (e.g. +HELP+) is not a path: ask for one.
+		if (!buf->Filename().empty() && !buf->IsVirtual()) {
 			// If first-time save to an existing path, confirm overwrite
 			if (fs_exists(buf->Filename())) {
 				ctx.editor.StartPrompt(Editor::PromptKind::Confirm, "Overwrite", "");
@@ -1130,7 +1124,7 @@ cmd_save_and_quit(CommandContext &ctx)
 				ctx.editor.SetStatus(err);
 				return false;
 			}
-		} else if (!buf->Filename().empty()) {
+		} else if (!buf->Filename().empty() && !buf->IsVirtual()) {
 			if (buf->SaveAs(buf->Filename(), err)) {
 				buf->SetDirty(false);
 				if (auto *sm = ctx.editor.Swap())
@@ -3162,7 +3156,7 @@ cmd_newline(CommandContext &ctx)
 							if (auto *u = buf->Undo())
 								u->mark_saved();
 						}
-					} else if (!buf->Filename().empty()) {
+					} else if (!buf->Filename().empty() && !buf->IsVirtual()) {
 						if (!buf->SaveAs(buf->Filename(), err)) {
 							ctx.editor.SetStatus(err);
 							proceed_to_close = false;
@@ -3974,6 +3968,14 @@ cmd_yank(CommandContext &ctx)
 	}
 	ensure_at_least_one_line(*buf);
 	int repeat = ctx.count > 0 ? ctx.count : 1;
+	// Bound the total: C-u 1000000 C-y of a large kill would allocate
+	// gigabytes (and bad_alloc or the OOM killer end the session).
+	constexpr std::size_t kMaxYankBytes = std::size_t{256} << 20;
+	if (text.size() * static_cast<std::size_t>(repeat) > kMaxYankBytes) {
+		ctx.editor.SetStatus("Yank too large (" + std::to_string(repeat) + " x " + std::to_string(text.size()) +
+		                     " bytes)");
+		return false;
+	}
 	std::string ins;
 	if (repeat == 1) {
 		ins = text;

Swap.cc

@@ -346,8 +346,8 @@ SwapManager::Rehome(Buffer *old_addr, Buffer *new_addr)
 void
 SwapManager::Attach(Buffer *buf)
 {
-	if (!buf)
+	if (!buf || buf->IsVirtual())
-		return;
+		return; // e.g. +HELP+: nothing to recover, and its name is not a path
 	std::lock_guard<std::mutex> lg(mtx_);
 	const bool fresh = journals_.find(buf) == journals_.end();
 	JournalCtx &ctx  = journals_[buf];

TerminalFrontend.cc

@@ -1,3 +1,4 @@
+#include <cstdio>
 #include <ncurses.h>
 #include <termios.h>
 #include <unistd.h>
@@ -12,6 +13,12 @@ TerminalFrontend::Init(int &argc, char **argv, Editor &ed)
 {
 	(void) argc;
 	(void) argv;
+	// Keys are read from stdin. Piped input would be executed as editor
+	// commands (and after EOF the loop spun at full CPU with no way to quit).
+	if (!isatty(STDIN_FILENO)) {
+		std::fprintf(stderr, "kte: standard input is not a terminal\n");
+		return false;
+	}
 	// Ensure Control keys reach the app: disable XON/XOFF and dsusp/susp bindings (e.g., ^S/^Q, ^Y on macOS)
 	{
 		struct termios tio{};
@@ -88,29 +95,50 @@ TerminalFrontend::Step(Editor &ed, bool &running)
 	// Handle resize and keep editor dimensions synced
 	int r, c;
 	getmaxyx(stdscr, r, c);
+	bool changed = first_frame_;
 	if (r != prev_r_ || c != prev_c_) {
 		resizeterm(r, c);
 		clear();
 		prev_r_ = r;
 		prev_c_ = c;
+		changed = true;
 	}
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
 
 	// Allow deferred opens (including swap recovery prompts) to run.
-	ed.ProcessPendingOpens();
+	if (ed.ProcessPendingOpens())
+		changed = true;
 
+	// Handle all pending input before drawing: one key per frame made a
+	// pasted block take a frame (and a full redraw) per character. The first
+	// read waits up to the configured timeout; the rest do not wait.
 	MappedInput mi;
-	if (input_.Poll(mi)) {
+	int handled = 0;
-		if (mi.hasCommand) {
+	while (handled < 4096 && input_.PollKey(mi)) {
+		changed = true;
+		if (mi.hasCommand)
 			Execute(ed, mi.id, mi.arg, mi.count);
+		if (ed.QuitRequested())
+			break;
+		if (++handled == 1)
+			timeout(0);
 	}
-	}
+	if (handled > 0)
+		timeout(16);
 
 	if (ed.QuitRequested()) {
 		running = false;
 	}
 
+	// Redraw after input or a resize, and otherwise about once a second
+	// (status messages, deferred work): redrawing every 16 ms kept a core
+	// busy on large or long-line files while idle.
+	const auto now = std::chrono::steady_clock::now();
+	if (changed || now - last_draw_ >= std::chrono::milliseconds(1000)) {
 		renderer_.Draw(ed);
+		last_draw_   = now;
+		first_frame_ = false;
+	}
 }
 
 

TerminalFrontend.h

@@ -2,6 +2,7 @@
  * TerminalFrontend - couples TerminalInputHandler + TerminalRenderer and owns ncurses lifecycle
  */
 #pragma once
+#include <chrono>
 #include <termios.h>
 #include <signal.h>
 
@@ -32,6 +33,9 @@ private:
 	TerminalRenderer renderer_{};
 	int prev_r_ = 0;
 	int prev_c_ = 0;
+	// Redraw only when something may have changed (see Step).
+	bool first_frame_ = true;
+	std::chrono::steady_clock::time_point last_draw_{};
 	// Saved terminal attributes to restore on shutdown
 	bool have_orig_tio_ = false;
 	struct termios orig_tio_{};

TerminalInputHandler.h

@@ -20,6 +20,15 @@ public:
 
 	bool Poll(MappedInput &out) override;
 
+	// Read one key if available. Returns false when no input was read; true
+	// when a key was consumed (out.hasCommand says whether it produced a
+	// command: prefixes such as C-k or ESC do not).
+	bool PollKey(MappedInput &out)
+	{
+		out = {};
+		return decode_(out);
+	}
+
 private:
 	bool decode_(MappedInput &out);
 

TerminalRenderer.cc

@@ -241,6 +241,45 @@ TerminalRenderer::Draw(Editor &ed)
 						return 0;
 					}
 				};
+				// Fast-forward to the scroll offset with the draw loop's own skip
+				// rules (a tab is skipped only if it ends at or before coloffs,
+				// any other character while it starts before coloffs), cached
+				// for the row's current content.
+				if (coloffs > 0 && src_i == 0) {
+					if (skip_cache_.size() < static_cast<std::size_t>(content_rows))
+						skip_cache_.resize(static_cast<std::size_t>(content_rows));
+					SkipCache &sc = skip_cache_[static_cast<std::size_t>(r)];
+					if (!(sc.valid && sc.buf == buf && sc.version == buf->Version() && sc.row == li &&
+					      sc.coloffs == coloffs)) {
+						std::size_t s = 0, c = 0;
+						while (s < line.size()) {
+							std::mbstate_t st = std::mbstate_t();
+							wchar_t w         = 0;
+							std::size_t n     = std::mbrtowc(&w, &line[s], line.size() - s, &st);
+							if (n == (size_t) -1 || n == (size_t) -2) {
+								w = static_cast<unsigned char>(line[s]);
+								n = 1;
+							} else if (n == 0) {
+								w = L'\0';
+								n = 1;
+							}
+							if (w == L'\t') {
+								const std::size_t next_tab = tabw - (c % tabw);
+								if (c + next_tab > coloffs)
+									break;
+								c += next_tab;
+							} else {
+								if (c >= coloffs)
+									break;
+								c += static_cast<std::size_t>(kte::CellWidth(w));
+							}
+							s += n;
+						}
+						sc = SkipCache{buf, buf->Version(), li, coloffs, s, c, true};
+					}
+					src_i      = sc.src;
+					render_col = sc.col;
+				}
 				while (written < cols) {
 					bool from_src = false;
 					wchar_t wch   = L' ';
@@ -391,7 +430,10 @@ TerminalRenderer::Draw(Editor &ed)
 		std::size_t cx            = buf->Curx();
 		int cur_y                 = static_cast<int>(cy) - static_cast<int>(buf->Rowoffs());
 		std::size_t rx_recomputed = 0;
-		if (cy < nlines) {
+		if (cy < nlines && cursor_cache_.valid && cursor_cache_.buf == buf &&
+		    cursor_cache_.version == buf->Version() && cursor_cache_.row == cy && cursor_cache_.cx == cx) {
+			rx_recomputed = cursor_cache_.rx;
+		} else if (cy < nlines) {
 			const std::string line_for_cursor = buf->GetLineString(cy);
 			std::size_t src_i_cur             = 0;
 			std::size_t render_col_cur        = 0;
@@ -420,6 +462,7 @@ TerminalRenderer::Draw(Editor &ed)
 				src_i_cur += len;
 			}
 			rx_recomputed = render_col_cur;
+			cursor_cache_ = CursorCache{buf, buf->Version(), cy, cx, rx_recomputed, true};
 		}
 		int cur_x = static_cast<int>(rx_recomputed) - static_cast<int>(buf->Coloffs());
 		if (cur_y >= 0 && cur_y < content_rows && cur_x >= 0 && cur_x < cols) {

TerminalRenderer.h

@@ -2,6 +2,9 @@
  * TerminalRenderer - ncurses-based renderer for terminal mode
  */
 #pragma once
+#include <vector>
+#include <cstdint>
+#include <cstddef>
 #include "Renderer.h"
 
 
@@ -12,4 +15,30 @@ public:
 	~TerminalRenderer() override;
 
 	void Draw(Editor &ed) override;
+
+private:
+	// Where a row's visible part starts (the draw loop's skip up to the
+	// horizontal scroll offset), cached per screen row. Scanning a very long
+	// line from column 0 on every frame made each redraw O(line length).
+	struct SkipCache {
+		const void *buf       = nullptr;
+		std::uint64_t version = 0;
+		std::size_t row       = 0;
+		std::size_t coloffs   = 0;
+		std::size_t src       = 0; // byte offset where drawing resumes
+		std::size_t col       = 0; // render column at that offset
+		bool valid            = false;
+	};
+
+	std::vector<SkipCache> skip_cache_;
+
+	// Render column of the cursor, cached the same way.
+	struct CursorCache {
+		const void *buf       = nullptr;
+		std::uint64_t version = 0;
+		std::size_t row       = 0;
+		std::size_t cx        = 0;
+		std::size_t rx        = 0;
+		bool valid            = false;
+	} cursor_cache_;
 };

tests/test_audit_regressions.cc

@@ -9,6 +9,7 @@
 #include "ErrorRecovery.h"
 #include "PieceTable.h"
 #include "RegexGuard.h"
+#include "Swap.h"
 #include "UndoTree.h"
 #include "syntax/HighlighterEngine.h"
 #include "syntax/HighlighterRegistry.h"
@@ -992,3 +993,36 @@ TEST(Audit_Save_KeepsSpecialModeBits)
 	ASSERT_EQ(::stat(f.c_str(), &st), 0);
 	ASSERT_EQ(st.st_mode & 07777, (mode_t) 06755);
 }
+
+
+// The help buffer's name is not a path: it is not journaled, and saving it
+// asks for a file name instead of writing ./+HELP+.
+TEST(Audit_HelpBuffer_NotJournaledOrSavedByName)
+{
+	TestHarness h;
+	Editor &ed = h.EditorRef();
+	ASSERT_TRUE(h.Exec(CommandId::ShowHelp));
+	Buffer *help = ed.CurrentBuffer();
+	ASSERT_TRUE(help->IsVirtual());
+	ASSERT_TRUE(h.Exec(CommandId::ToggleReadOnly));
+	ASSERT_TRUE(h.Exec(CommandId::InsertText, "x"));
+	ed.Swap()->Flush(help);
+	ASSERT_TRUE(!std::filesystem::exists(kte::SwapManager::ComputeSwapPathForTests(*help)));
+	ASSERT_TRUE(h.Exec(CommandId::Save));
+	ASSERT_TRUE(ed.PromptActive());
+	ASSERT_TRUE(ed.CurrentPromptKind() == Editor::PromptKind::SaveAs);
+	ASSERT_TRUE(!std::filesystem::exists("+HELP+"));
+	ASSERT_TRUE(h.Exec(CommandId::Refresh));
+}
+
+
+// A huge repeated yank is refused rather than allocating without bound.
+TEST(Audit_Yank_HugeRepeatRefused)
+{
+	TestHarness h;
+	Editor &ed = h.EditorRef();
+	ed.KillRingPush(std::string(1 << 20, 'k'));
+	ASSERT_TRUE(!h.Exec(CommandId::Yank, std::string(), 1000000));
+	ASSERT_EQ(h.Buf().Nrows(), (std::size_t) 1);
+	ASSERT_EQ(h.Line(0), std::string());
+}