termio/exec: clear screen should erase rows and shift up

src/terminal/PageList.zig

@@ -1871,12 +1871,10 @@ pub fn eraseRows(
             const old_dst = dst.*;
             dst.* = src.*;
             src.* = old_dst;
-        }
 
-        // We don't even bother deleting the data in the swapped rows
-        // because erasing in this way yields a page that likely will never
-        // be written to again (its in the past) or it will grow and the
-        // terminal erase will automatically erase the data.
+            // Clear the old data in case we reuse these cells.
+            chunk.page.data.clearCells(src, 0, chunk.page.data.size.cols);
+        }
 
         // Update any tracked pins to shift their y. If it was in the erased
         // row then we move it to the top of this page.

src/terminal/Screen.zig

@@ -2395,6 +2395,35 @@ test "Screen eraseRows history with more lines" {
     }
 }
 
+test "Screen eraseRows active partial" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var s = try Screen.init(alloc, 5, 5, 0);
+    defer s.deinit();
+
+    try s.testWriteString("1\n2\n3");
+
+    {
+        const str = try s.dumpStringAlloc(alloc, .{ .active = .{} });
+        defer alloc.free(str);
+        try testing.expectEqualStrings("1\n2\n3", str);
+    }
+
+    s.eraseRows(.{ .active = .{} }, .{ .active = .{ .y = 1 } });
+
+    {
+        const str = try s.dumpStringAlloc(alloc, .{ .active = .{} });
+        defer alloc.free(str);
+        try testing.expectEqualStrings("3", str);
+    }
+    {
+        const str = try s.dumpStringAlloc(alloc, .{ .screen = .{} });
+        defer alloc.free(str);
+        try testing.expectEqualStrings("3", str);
+    }
+}
+
 test "Screen: clearPrompt" {
     const testing = std.testing;
     const alloc = testing.allocator;

src/termio/Exec.zig

@@ -479,10 +479,9 @@ pub fn clearScreen(self: *Exec, history: bool) !void {
         // If we're not at a prompt, we just delete above the cursor.
         if (!self.terminal.cursorIsAtPrompt()) {
             if (self.terminal.screen.cursor.y > 0) {
-                self.terminal.screen.clearRows(
+                self.terminal.screen.eraseRows(
                     .{ .active = .{ .y = 0 } },
                     .{ .active = .{ .y = self.terminal.screen.cursor.y - 1 } },
-                    false,
                 );
             }