editor.setDecorations does not render all contentText correctly

[cunbidun]

Type: Bug

This extension creates a decoration type that displays a “before” text label with a specific foreground and background color. It iterates over a set of characters, generating every possible two-character combination from that set.

import * as vscode from 'vscode';

export function activate(context: vscode.ExtensionContext) {
	const labelDecoration = vscode.window.createTextEditorDecorationType({
		before: {
			color: 'black',
			backgroundColor: '#a3be8c',
		},
	});
	const labelDecorationQuestion = vscode.window.createTextEditorDecorationType({
		before: {
			color: 'black',
			backgroundColor: '#ebcb8b',
			contentText: '?'
		},
	});

	// Map of label character to target position
	let labelMap: Map<string, { editor: vscode.TextEditor, position: vscode.Position }> = new Map();

	// Define the character pool for labels: lowercase, then uppercase, then digits
	const labelChars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789!@#$%^&*()-_=+[]{}|;:\'",.<>/`~\\';

	const editor = vscode.window.activeTextEditor
	const decorationOptions: vscode.DecorationOptions[] = [];
	let line = 0;
	for (const c1 of labelChars) {
		let cnt = 0;
		for (const c2 of labelChars) {
			decorationOptions.push({
				range: new vscode.Range(new vscode.Position(line, cnt), new vscode.Position(line, cnt + 1)),
				renderOptions: {
					before: { contentText: c1 + c2 }
				}
			});
			cnt += 3;
		}
		line += 1
	}
	if (editor) {
		editor.setDecorations(labelDecoration, decorationOptions);
	}
}

Expected Behavior Each unique pair of characters (c1 + c2) should appear exactly once in the “before” content on its corresponding position.

Actual Behavior Some lines or columns show repeated decorations, while others skip certain pairs. The console logs confirm each pair is generated distinctly, but in the editor the decorations appear partially duplicated or re‑ordered. Example: After bz, I expect the next text to be bA

VS Code version: Code 1.97.2 (e54c774e0add60467559eb0d1e229c6452cf8447, 2025-02-12T23:20:35.343Z) OS version: Linux x64 6.13.5 Modes:

System Info

Item	Value
CPUs	13th Gen Intel(R) Core(TM) i7-13700K (24 x 5300)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: disabled_software vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: disabled_off webnn: disabled_off
Load (avg)	1, 1, 1
Memory (System)	31.09GB (15.75GB free)
Process Argv	--ozone-platform-hint=auto --enable-features=WaylandWindowDecorations --enable-wayland-ime=true flash.vscode --crash-reporter-id ac05c1a8-c8ea-496b-8089-200a0791d978
Screen Reader	no
VM	0%
DESKTOP_SESSION	undefined
XDG_CURRENT_DESKTOP	Hyprland
XDG_SESSION_DESKTOP	Hyprland
XDG_SESSION_TYPE	wayland

Extensions: none

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dwcopilot:31170013
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customenabled:31248079
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[vs-code-engineering[bot]]

Thanks for creating this issue! It looks like you may be using an old version of VS Code, the latest stable release is 1.98.0. Please try upgrading to the latest version and checking whether this issue remains.

Happy Coding!