cursor-lang/README.md

cursor-lang

Русская версия

The WPF application displays the keyboard layout at the cursor.

Cloning

Binary assets — the exe icon and the MSIX logos — are stored in Git LFS, so git-lfs has to be installed before cloning:

git lfs install
git clone git@git.alrakis.kz:alrakis/cursor-lang.git

Cloning without it succeeds but leaves text pointer files in place of the images, and the build then fails on an unreadable icon. An existing clone is repaired with git lfs install followed by git lfs pull.

Running it while working on it

dotnet run --project CursorLang.Agent

That is the whole application, not just the background half: building the agent puts the settings window next to it, because that is where the agent looks for it — the tray menu starts it by path, and an installation has the two in one folder. Build the agent alone and the Settings item would silently do nothing.

Rider and Visual Studio pick the launch profiles up from CursorLang.Agent/Properties/launchSettings.json and CursorLang.Settings/Properties/launchSettings.json, so the run configuration dropdown offers three:

Profile	What it does
Agent	The user's launch: tray icon and the settings window straight away
Agent (started by Windows)	Adds --startup: tray only, no window — the sign-in case
Settings	The settings window on its own, with no agent behind it

Both halves read %APPDATA%\CursorLang\settings.json, the same file the installed application uses — there is one code path resolving it and both call it. Debugging therefore edits the real settings; that is deliberate, since watching the agent pick up a change made in the window is most of what there is to watch.

To step through both at once, turn on attaching to child processes in the debugger: the settings window is started by the agent as a separate process, and without that the debugger stays with the agent.

Administrator rights

The app runs as the ordinary user. Elevation was dropped so that the app can be published in the Microsoft Store: MSIX packages always run in the context of the signed-in user, and Store policy rejects apps that need administrator rights for any part of their functionality.

The cost is the optional Caps Lock hotkey. While a window of a higher integrity level holds the focus — Task Manager, Registry Editor, UAC prompts — Windows neither delivers keystrokes to the low-level hook nor accepts the layout change request, so the hotkey does nothing there. Reading the layout of a foreign window is not restricted, so the tooltip itself keeps working everywhere.

Two processes

The app is two executables sharing one folder.

CursorLang.exe is the agent: the keyboard hook, the layout polling, the tooltip and the tray icon. It is what Windows starts at sign-in and what sits in the tray all day, so it is built without WPF — a background process that carries the rendering stack costs around a hundred megabytes for a tooltip it draws with Win32 in eight. It holds under 9 MB instead.

CursorLang.Settings.exe is the settings window, and nothing else. The agent starts it from the tray menu; closing the window ends the process, and the memory WPF took goes back to the system. The price is a cold start of half a second or so the next time the window is asked for.

CursorLang.Core.dll is what both hold in common: the models, the settings file, the layout tracking. No UI, and it must stay that way — whatever lands there lands in the background process.

Everything the window has to say to the agent goes through settings.json and nothing else. The window writes it — whole, into a temporary file moved into place in one step — and then posts a registered window message to the agent, which re-reads. The message carries no data: sending the changed values along would make the file stop being the only source of truth. An agent that is not running is a normal case — the window works the same. Nobody watches the file: it has one writer, and that writer speaks up.

The one word in the other direction is the last one: Exit in the tray menu asks an open settings window to close before the agent goes, so that no window is left belonging to nothing. It travels as a named event of the session rather than a window message — the agent starts that process and deliberately keeps no handle to it. Nobody listening is the usual case, and it is a normal answer.

The tray

The settings window is a guest on the screen rather than the app itself: it shows up after the installation and whenever the icon or its menu is asked for. Both buttons in its title bar mean what they say — the window closes and its process ends. The way out of the app itself is the Exit item of the tray menu — and it closes an open settings window along with the agent.

The menu of the icon is a system one, drawn by Windows. Its captions still follow the language chosen in the settings, but the theme no longer reaches it: a WPF menu would mean the whole rendering stack in the background process, which is the one thing that process is built to avoid.

Started by Windows itself, the app shows no window at all and goes straight to the tray — the user asked for it to be there when they sign in, not for a window to greet them every morning. The two builds tell such a launch apart differently: the registry entry of an unpacked build carries the --startup argument, while a package has no say in its command line, and Windows is asked about the activation instead.

Should Windows refuse the icon — there is no notification area in a session without a desktop — the agent opens the settings window whatever the launch was. The alternative would be an app the user can neither see nor quit.

Startup

Startup is switched on from the app's settings by whichever means the build has. A package declares it in the manifest as a windows.startupTask. A build unpacked into a folder registers itself the way desktop programs always have — under HKCU\Software\Microsoft\Windows\CurrentVersion\Run, which needs no administrator rights. The command names CursorLang.exe — the agent, not the settings window the checkbox was clicked in — and ends with --startup: that is how the agent tells a launch of Windows' own doing from a launch by the user.

Either way Windows lists the app in Settings — Apps — Startup; if the user turns it off there, the app can no longer turn it back on and says so instead of silently failing. The registry entry stays where it is in that case: Windows keeps the user's verdict apart from it, under StartupApproved, and the app obeys it.

Settings

Where settings.json lives depends on how the app was installed. A separate install keeps it in %APPDATA%\CursorLang. The packaged build keeps it in the package's own data folder, which Windows removes together with the app — Store apps are expected to leave nothing behind.

On its first run the packaged build picks up the settings left by a separate install and copies them over. The original file stays where it is: both builds may be installed side by side, and the app has no business deleting settings it does not own.

Everything about the popup belongs to a placement mode rather than to the app, and the file keeps a section per mode — AtCursor, AtCaret and FixedPoint. Each of them holds the side, the offset, the font size, the opacity and both colours. The popup next to the caret sits inside a text being read and is wanted small and quiet; the one in the corner of the monitor is looked for on purpose and is wanted large. A look shared by the modes meant setting it up again after every switch, so the settings window shows the look of the mode chosen above it and writes into that mode alone.

What the side means differs by mode, and each of them has a type saying so. Next to the cursor it is any of the six corners and sides. Next to the caret it is left or right and nothing else — above or below the caret is exactly where the next line of the text is, so the popup would cover what is being read. For the fixed point it is a place on the monitor, and the offset is the distance from its edge: in the middle there is no edge to stand off from, so choosing the middle puts the offset back to zero and the settings window shows it greyed out. It stays in place rather than leaving the section — a row that comes and goes would move everything below it on every switch of the place.

Not every application reports where its caret is, and next to the caret is then nowhere. The popup goes to the fixed point instead — the place, the offset and the look all from that mode, none of them from the caret one. The mouse cursor would be the nearer fallback and is the wrong one: it is wherever it was last left, off to a side or on another monitor, while the eyes are on the caret. The fixed point is always in the same place, so it is known where to look — and the look must come with it, since a popup set small and quiet for the middle of a text goes unnoticed in the corner of a monitor.

Which mode the look belongs to is explained in a tooltip next to the mode itself rather than by a line of text in the section: the sliders below show other numbers after a switch of the mode, and that is a question asked once.

Updates

The Store updates the app, and the app itself does nothing about it: there is no updates section in the window, no request to the network and no code for either.

That is not a matter of taste but of what a signature costs. Windows installs an MSIX only when it trusts the signature on it, and a publicly trusted code signing certificate has turned out to be beyond reach — the certificate authorities that sell them will not issue one here, and those that would keep the key in a cloud HSM will not either, while a certificate on a USB token cannot be shipped in. Without a signature a package installs nowhere but a machine in developer mode, so there is nothing to hand out from a release and nothing for an updater to find. The Store signs the package with its own certificate and updates the app by itself, which leaves the whole question to it.

The version of the running app is in the title of the settings window: CursorLang 1.2.3 — Settings. It is nowhere else in the interface, and it is there so that a bug report can name it.

Tests

dotnet test

There is a suite per project — CursorLang.Core.Tests, CursorLang.Agent.Tests and CursorLang.Settings.Tests — all on xUnit, with the fakes and the helpers in a library of their own, CursorLang.Tests.Shared. That library knows nothing about xUnit: the one thing that wanted an assertion says so with an exception instead. Core's suite carries no WPF reference, which is a check in itself: anything that would drag WPF into the background process fails to compile there.

Half of the app — windows, timers, the keyboard hook — only works on an STA thread with a message loop, so the tests keep one such thread for the whole run and drive everything through it. For Core and the agent that thread runs a plain Win32 loop (CursorLang.Tests.Shared/Pump.cs); the settings window gets a WPF dispatcher instead.

A few checks need a real foreground window: the caret position and the layout switch request are only observable there. Windows does not always grant the right to bring a window forward, and those checks report themselves as skipped rather than as failures — there is nothing to verify without a foreground window. The end-to-end checks start the built application as a separate process and skip themselves if the app is already running: interfering with someone else's running instance is not their business.

Coverage is collected with:

dotnet test --collect:"XPlat Code Coverage" --settings coverage.runsettings

What stays uncovered is what a test process cannot reach: the code paths that require an MSIX package identity — StartupTask and the package data folder — and the composition roots — App.xaml.cs and Agent.cs — which are exercised end-to-end instead. One of those end-to-end checks reads the module list of the running agent and fails if any part of the WPF renderer is in it.

Continuous integration

The pipelines live in .gitea/workflows and run on Gitea Actions. A pull request into master is built and tested; a tag of the form v1.2.3 is built, tested and packed into an MSIX, which is left in the artifacts of the run. The version is taken from the tag alone — a tag shaped any other way stops the run right at the start. The package version ends up as 1.2.3.0: the Store takes four numbers and keeps the last one for itself, so the tag has no say in it.

Both pipelines ask for a Windows runner labelled windows-x64 with the .NET 10 SDK and git-lfs on it. The checkout pulls LFS files: without them the icon is a text pointer and the build fails on it. The runner is better off working in an interactive desktop session: the tests raise real windows, and the checks that need a desktop of their own — the end-to-end ones, and those that ask for the foreground window or the caret — skip themselves on a runner that lives as a service in session 0, where there is no desktop to show a window on.

The package goes to the Store and nowhere else: it is unsigned, and Partner Center puts its own signature on it. So the run leaves it in the artifacts under the name msix-1.2.3.0, where whoever uploads it picks it up by hand; nothing is attached to the release, which Gitea makes for the tag by itself and which carries the tag alone. An unsigned package hanging off a release would look like something to install and install nowhere — see the section on updates.

The identity comes from repository variables and falls back to the defaults of the script when unset: MSIX_IDENTITY_NAME, MSIX_PUBLISHER and MSIX_PUBLISHER_DISPLAY_NAME. Together the identity and the publisher decide the family name of the package, so both have to stay as they are from version to version, or the Store takes the next one for a different app.

Building the MSIX package

Neither Visual Studio nor the Windows SDK is required — makeappx comes from a NuGet package. The full publishing procedure — from opening a developer account to submitting for certification — is written up in Packaging/PUBLISHING.RU.md (Russian only).

# One-off: draw the logos and the exe icon (already committed, rerun after edits)
powershell -File Packaging\New-Assets.ps1

# A check on your own machine
powershell -File Packaging\build-msix.ps1

# For Partner Center — the identity is the one reserved there
powershell -File Packaging\build-msix.ps1 -Version 1.0.1.0 `
    -IdentityName 12345AleksandrNeichev.CursorLang -Publisher "CN=ABCD1234-..."

The result is artifacts\packages\CursorLang-<version>-x64.msix. Upload it to Partner Center as it is.

Only x64 is built. An arm64 build would double the size of every release for the sake of machines that run the x64 one under emulation anyway.

Nothing here is signed: the Store signs the package itself, and for installing it on this machine the layout is registered instead — see -Install below.

The app ships with its own copy of .NET: Windows does not include .NET 10, and MSIX cannot install a runtime as a package dependency.

To see the package working on this machine, build it with -Install:

pwsh -File Packaging\build-msix.ps1 -Install

The application then shows up in the Start menu like any installed one. What gets registered is the layout the package is made of rather than the package file, so no signature is needed — only Developer Mode. The flip side is that the application runs straight out of artifacts\layout, and a rebuild would pull the files out from under it; the script removes such a registration before it wipes the folder, whether or not -Install was asked for. A copy installed from the Store answers to the same name and is left alone.

To remove it by hand:

Remove-AppxPackage (Get-AppxPackage -Name AleksandrNeichev.CursorLang).PackageFullName

Building the installer

The same application also comes as an ordinary MSI, for handing round outside the Store — to try it out before the Store has passed judgement, or if it never does. Nothing has to be installed beyond the .NET SDK: WiX comes from a NuGet package, the same way makeappx does.

# Build it and run it afterwards, to see what a user sees
pwsh -File Packaging\build-installer.ps1 -Install

# Everything a release needs
pwsh -File Packaging\build-installer.ps1 -Version 1.0.1

The result is artifacts\installers\CursorLang-<version>-x64.msi. Everything travels inside the .msi; there is no cabinet to send alongside it.

It installs for the current user alone, into %LOCALAPPDATA%\Programs\CursorLang, and so asks for no administrator rights and no consent dialog. Uninstalling goes through Apps in Settings like any other program and takes the startup entry with it — otherwise Windows would go on listing an application that is no longer there.

Nobody signs the installer, so Windows warns about an unknown publisher and the user has to insist. Buying a certificate would not silence it at once either: SmartScreen goes by reputation, and a fresh certificate has none until enough people have installed the application.

Two things about the WiX project are worth knowing before touching it.

It pins WiX 5 rather than the current 7: from version 6 the toolset asks every build to accept the Open Source Maintenance Fee licence — free below $10,000 of yearly revenue, but a decision for a person rather than for a build script.

And it builds without MSI validation. The ICE checks run inside the Windows Installer service, which a build agent cannot reach: every check comes back as WIX0217 and the build dies on close to a hundred of them. On an ordinary desktop machine the service does answer, and validation is one switch away:

dotnet build Packaging\Installer\CursorLang.wixproj -p:SuppressValidation=false

Three of its rules stay suppressed even then. MSI assumes an installation for the whole machine, and installing into the user's own profile trips rules that describe exactly what was intended here.