From 9085cb5bfdd0b78ff3a62c0c71fc231dd7b5052a Mon Sep 17 00:00:00 2001
From: Gabriel Schneider <gbrls@0x4200.cafe>
Date: Sun, 9 Aug 2026 10:41:33 -0300
Subject: replace ArrayLists with bounded storage

---
 src/term_pane.zig | 55 ++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 42 insertions(+), 13 deletions(-)

(limited to 'src/term_pane.zig')

diff --git a/src/term_pane.zig b/src/term_pane.zig
index 47123ceb..5e50e15d 100644
--- a/src/term_pane.zig
+++ b/src/term_pane.zig
@@ -35,14 +35,18 @@ pub fn shellRows(p: *Pardes, pane: *Pane) ![]const []const u8 {
     const arena = p.scratch.allocator();
     const full = try pane.vt.screens.active.dumpStringAlloc(arena, .{ .screen = .{} });
     var pit = pane.vt.screens.active.pages.rowIterator(.right_down, .{ .screen = .{} }, null);
-    var ls: std.ArrayList([]const u8) = .empty;
-    var it = std.mem.splitAny(u8, full, "\n");
+    // split yields one more item than delimiters; the extra final slot is the
+    // cursor row retained below.
+    const rows = try arena.alloc([]const u8, std.mem.count(u8, full, "\n") + 2);
+    var n: usize = 0;
+    var it = std.mem.splitScalar(u8, full, '\n');
     while (it.next()) |raw| {
         const is_prompt = if (pit.next()) |pin| pin.rowAndCell().row.semantic_prompt != .none else false;
-        try ls.append(arena, if (is_prompt) "" else raw);
+        rows[n] = if (is_prompt) "" else raw;
+        n += 1;
     }
-    try ls.append(arena, "");
-    return ls.items;
+    rows[n] = "";
+    return rows;
 }
 
 /// The body a terminal renders: the viewport's shell rows (prompt rows blanked
@@ -51,21 +55,35 @@ pub fn shellRows(p: *Pardes, pane: *Pane) ![]const []const u8 {
 pub fn bodyText(arena: std.mem.Allocator, pane: *Pane) ![]const u8 {
     const raw = try pane.vt.plainString(arena);
     var prompts = pane.vt.screens.active.pages.rowIterator(.right_down, .{ .viewport = .{} }, null);
-    var vp: std.ArrayList([]const u8) = .empty;
+    const vp = try arena.alloc([]const u8, std.mem.count(u8, raw, "\n") + 1);
     var lines = std.mem.splitScalar(u8, raw, '\n');
+    var n: usize = 0;
     while (lines.next()) |ln| {
         const is_prompt = if (pane.mode != .tty)
             if (prompts.next()) |pin| pin.rowAndCell().row.semantic_prompt != .none else false
         else
             false;
-        try vp.append(arena, if (is_prompt) "" else ln);
+        vp[n] = if (is_prompt) "" else ln;
+        n += 1;
     }
+    std.debug.assert(n == vp.len);
+
+    const len = fillBody(null, pane, vp);
+    const out = try arena.alloc(u8, len);
+    const filled = fillBody(out, pane, vp);
+    std.debug.assert(filled == out.len);
+    return out;
+}
+
+/// Run the terminal body row walk. A null destination counts bytes; a slice
+/// fills the exact allocation made from that count.
+fn fillBody(dst: ?[]u8, pane: *Pane, viewport: []const []const u8) usize {
     const goff: i32 = @intCast(pane.vt.screens.active.pages.scrollbar().offset);
     const off = pane.scroll();
     var g: i32 = pane.gridRow(off);
     // the buffer can start above the viewport: drop the lines scrolled past
     var skip: usize = if (pane.ovl) |o| @intCast(@max(0, off - pane.surfRow(o.row))) else 0;
-    var out: std.ArrayList(u8) = .empty;
+    var written: usize = 0;
     var n: usize = 0;
     while (n < pane.rows) {
         if (pane.mode != .tty) if (pane.ovl) |o| if (g == o.row) {
@@ -74,21 +92,32 @@ pub fn bodyText(arena: std.mem.Allocator, pane: *Pane) ![]const u8 {
             while (bit.next()) |ln| : (k += 1) {
                 if (k < skip) continue;
                 if (n >= pane.rows) break;
-                if (n > 0) try out.append(arena, '\n');
-                try out.appendSlice(arena, ln);
+                if (n > 0) {
+                    if (dst) |out| out[written] = '\n';
+                    written += 1;
+                }
+                if (dst) |out| @memcpy(out[written..][0..ln.len], ln);
+                written += ln.len;
                 n += 1;
             }
             skip = 0;
             g += o.rows;
             continue;
         };
-        if (n > 0) try out.append(arena, '\n');
+        if (n > 0) {
+            if (dst) |out| out[written] = '\n';
+            written += 1;
+        }
         const vi = g - goff;
-        if (vi >= 0 and @as(usize, @intCast(vi)) < vp.items.len) try out.appendSlice(arena, vp.items[@intCast(vi)]);
+        if (vi >= 0 and @as(usize, @intCast(vi)) < viewport.len) {
+            const line = viewport[@intCast(vi)];
+            if (dst) |out| @memcpy(out[written..][0..line.len], line);
+            written += line.len;
+        }
         n += 1;
         g += 1;
     }
-    return out.items;
+    return written;
 }
 
 /// tty colors: recolor each body cell from the emulator's own style so shell
-- 
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