support DECCOLM

This gets vttest page 1 and page 2 now FULL passing.

We now crash on page 3. This is a lingering bug in our grid code
though and we need to find it anyways so we'll keep the crash in.

src/Window.zig

@@ -809,23 +809,20 @@ pub fn setMode(self: *Window, mode: terminal.Mode, enabled: bool) !void {
 
         .bracketed_paste => self.bracketed_paste = true,
 
-        .enable_mode_3 => self.terminal.modes.enable_mode_3 = @boolToInt(enabled),
-        .@"132_column" => mode3: {
-            // TODO: test this
+        .enable_mode_3 => {
+            // Disable deccolm
+            self.terminal.setDeccolmSupported(enabled);
 
-            // Do nothing if "enable mode 3" is not set.
-            if (self.terminal.modes.enable_mode_3 == 0) break :mode3;
-
-            // Set it
-            self.terminal.modes.@"132_column" = @boolToInt(enabled);
-
-            // TODO: do not clear screen flag mode
-            self.terminal.eraseDisplay(.complete);
-            self.terminal.setCursorPos(1, 1);
-
-            // TODO: left/right margins
+            // Force resize back to the window size
+            self.terminal.resize(self.alloc, self.grid.size.columns, self.grid.size.rows) catch |err|
+                log.err("error updating terminal size: {}", .{err});
         },
 
+        .@"132_column" => try self.terminal.deccolm(
+            self.alloc,
+            if (enabled) .@"132_cols" else .@"80_cols",
+        ),
+
         else => if (enabled) log.warn("unimplemented mode: {}", .{mode}),
     }
 }

src/terminal/Terminal.zig

@@ -52,8 +52,8 @@ modes: packed struct {
     origin: u1 = 0, // 6
     autowrap: u1 = 1, // 7
 
-    @"132_column": u1 = 0, // 3,
-    enable_mode_3: u1 = 0, // 40
+    deccolm: u1 = 0, // 3,
+    deccolm_supported: u1 = 0, // 40
 } = .{},
 
 /// Scrolling region is the area of the screen designated where scrolling
@@ -142,10 +142,58 @@ pub fn primaryScreen(self: *Terminal, options: AlternateScreenOptions) void {
     if (options.cursor_save) self.restoreCursor();
 }
 
+/// The modes for DECCOLM.
+pub const DeccolmMode = enum(u1) {
+    @"80_cols" = 0,
+    @"132_cols" = 1,
+};
+
+/// DECCOLM changes the terminal width between 80 and 132 columns. This
+/// function call will do NOTHING unless `setDeccolmSupported` has been
+/// called with "true".
+///
+/// This breaks the expectation around modern terminals that they resize
+/// with the window. This will fix the grid at either 80 or 132 columns.
+/// The rows will continue to be variable.
+pub fn deccolm(self: *Terminal, alloc: Allocator, mode: DeccolmMode) !void {
+    // TODO: test
+
+    // We need to support this. This corresponds to xterm's private mode 40
+    // bit. If the mode "?40" is set, then "?3" (DECCOLM) is supported. This
+    // doesn't exactly match VT100 semantics but modern terminals no longer
+    // blindly accept mode 3 since its so weird in modern practice.
+    if (self.modes.deccolm_supported == 0) return;
+
+    // Enable it
+    self.modes.deccolm = @enumToInt(mode);
+
+    // Resize -- we can set cols to 0 because deccolm will force it
+    try self.resize(alloc, 0, self.rows);
+
+    // TODO: do not clear screen flag mode
+    self.eraseDisplay(.complete);
+    self.setCursorPos(1, 1);
+
+    // TODO: left/right margins
+}
+
+/// Allows or disallows deccolm.
+pub fn setDeccolmSupported(self: *Terminal, v: bool) void {
+    self.modes.deccolm_supported = @boolToInt(v);
+}
+
 /// Resize the underlying terminal.
-pub fn resize(self: *Terminal, alloc: Allocator, cols: usize, rows: usize) !void {
+pub fn resize(self: *Terminal, alloc: Allocator, cols_req: usize, rows: usize) !void {
     // TODO: test, wrapping, etc.
 
+    // If we have deccolm supported then we are fixed at either 80 or 132
+    // columns depending on if mode 3 is set or not.
+    // TODO: test
+    const cols: usize = if (self.modes.deccolm_supported == 1)
+        @as(usize, if (self.modes.deccolm == 1) 132 else 80)
+    else
+        cols_req;
+
     // Resize our tabstops
     // TODO: use resize, but it doesn't set new tabstops
     if (self.cols != cols) {

src/terminal/stream.zig

@@ -48,9 +48,9 @@ pub fn Stream(comptime Handler: type) type {
             //log.debug("char: {x}", .{c});
             const actions = self.parser.next(c);
             for (actions) |action_opt| {
-                // if (action_opt) |action| {
-                //     log.info("action: {}", .{action});
-                // }
+                if (action_opt) |action| {
+                    log.info("action: {}", .{action});
+                }
                 switch (action_opt orelse continue) {
                     .print => |p| if (@hasDecl(T, "print")) try self.handler.print(p),
                     .execute => |code| try self.execute(code),