taiga-ui-migration

Goal

Successfully migrate a Taiga UI project to the next major version while:

• Preserving runtime behavior, template output, styles, and build tooling
• Handling post-schematics TODOs safely and systematically
• Identifying and resolving common migration issues
• Minimizing breaking changes through careful verification

Step 0: Gather Context Before Acting

CRITICAL: Before executing any command or editing any file, collect and confirm the following:

Question	Where to find it
Source and target major versions	Ask the user if not stated
Package manager (npm / yarn / pnpm)	package.json → packageManager field or lock-file presence
Build system (Angular CLI / Nx)	Presence of nx.json or angular.json
Monorepo: how many apps/libs affected	nx.json → projects, or angular.json → projects
Custom webpack / ESBuild config	angular.json → builder field

If the Taiga UI MCP server is available, use get_migration_guide now to load the {CURRENT_MAJOR} → {NEXT_MAJOR} migration notes before proceeding. This gives you authoritative breaking-change information for the entire session.

Do not proceed to Phase 1 until every item in the table is resolved.

Before You Start - Prerequisites Checklist

• Node.js: Use Node.js LTS version
• NPM: Version 10 or higher (or equivalent for yarn/pnpm)
• Current Taiga UI: Update to the latest version of v{CURRENT_MAJOR} first
• Angular: Update to a version compatible with v{NEXT_MAJOR} (check migration guide)
• Prettier: Set endOfLine option to auto to prevent line ending issues after migration

⛔ NEVER use --legacy-peer-deps, --force, or any flag that bypasses dependency resolution. These flags hide real version conflicts that will break at runtime. Resolve conflicts explicitly instead.

Migration Workflow

Phase 1: Run Migration Schematics

For Angular CLI projects:

ng update @taiga-ui/cdk

For Nx projects:

nx migrate @taiga-ui/cdk
nx migrate --run-migrations=migrations.json

Phase 2: Review Changed Code

After schematics complete:

1. Review all changed code lines - Some changes contain new code comments (like // TODO: (Taiga UI migration)). These comments typically contain instructions for manually migrating deleted entities with new alternatives.

2. Check for @taiga-ui/legacy imports - You may find new imports from @taiga-ui/legacy. This is a transitional package for outdated entities before their full removal:

   • Everything in this package in v{NEXT_MAJOR} will be removed in v{NEXT_MAJOR+1}
   • You can continue using them temporarily
   • Most deprecated entities have modern alternatives marked with @deprecated tag (IDEs display these as stricken-through)
   • Strongly recommended: Replace with modern alternatives as soon as possible

Phase 3: Handle Migration TODOs

Handle post-schematics TODOs without breaking runtime behavior, template output, styles, or build tooling.

Core Rules for TODOs

• TODOs are not permission to guess. They are a prompt to verify what is actually safe to change.
• Fix all actionable TODOs in scope, but only after proving each fix from nearby code and usage.
• Prefer the smallest possible change that preserves current behavior.
• Never remove a deprecated package, import, or utility just because a TODO suggests it unless the codebase proves it is unused.
• If a fix could change logic, generated markup, CSS application, or script behavior, validate the surrounding usage first.
• If the safe fix is unclear, ask the user instead of inventing code.

TODO Processing Order

Process TODOs starting from shared modules and barrel files (index.ts, public-api.ts) to unblock consumers, then move to services, components, and finally style entry points. Complete all TODOs in a file before moving to the next one. If a file cannot be completed, add a Quick Entry to MIGRATION_ISSUES.md and continue.

TODO Classification → Required Question Template

Category	Stop condition	Question to ask
Template/DI (high priority)	Direct replacement exists	Usually safe to fix without asking
Style package removal	Any class from that package found in templates	"I found <className> used in <file>. Should I keep the old style package until these are migrated?"
No direct replacement	TODO explicitly says so	"The migration notes say <API> was removed with no direct replacement. What behavior should replace it?"
Dynamic binding	[input]="expr" where expr is runtime value	"The binding [appearance]="mode" uses a runtime value. Should the new API accept the same values?"
Multiple valid paths	More than one replacement exists in docs	"Two replacements exist: <A> and <B>. Which one matches your intended behavior?"
Warning-only	TODO indicates manual decision needed	"This TODO requires your decision: <TODO text>. What is your preferred approach?"

Classification examples:

• TODO: replace TuiButtonModule with TuiButton → Template/DI (high priority, usually safe)
• TODO: remove @taiga-ui/styles import → Style package (STOP, check usage first)
• TODO: migrate to standalone component API → TypeScript (medium priority, check consumers)
• TODO: this API was removed, no direct replacement → Warning-only (ask user)

TODO Workflow

1. Identify and classify the TODO using the table above
2. Look up the replacement using MCP (if available):
   • For component replacements: call get_component_example with the new component name
   • For architectural changes: call get_overview or migration_guide
   • Skip this step only if the replacement is unambiguous from local code context alone
3. Trace real usage before editing anything:
   • Search the current component, template, styles, and nearby files for direct references
   • For style-related TODOs, follow the Style Package Removal algorithm below
   • Confirm whether the TODO targets one site or a broader pattern
4. Decide whether the TODO is safely actionable:
   • If there is a one-to-one replacement and it preserves behavior, apply it
   • If a deprecated package is mentioned, check whether any runtime, template, or style usage still depends on it before deleting it
   • If multiple replacements are plausible, or the fix depends on dynamic bindings or generated output, stop and ask the user using the question template
5. Apply the smallest safe fix:
   • Keep changes localized
   • Avoid broad refactors unless they are required to preserve behavior
   • Do not remove imports, packages, or scripts unless the surrounding evidence supports that removal
6. Verify the result:
   • Re-read the touched area to make sure logic, classes, and selectors still line up
   • Run the narrowest available check for the affected slice when possible
   • If the change still feels ambiguous after verification, do not expand the patch; ask the user

Phase 4: Troubleshooting

Problem: TypeScript errors TS6133 - variable is declared but its value is never read

Solution: Migration schematics don't include code formatting on purpose (it would slow down execution). Use your IDE or linter:

• WebStorm: Right-click on root folder → "Optimize imports" (removes all unused imports recursively)
• Visual Studio Code: Use "Organize Imports" folder source action across all files recursively
• ESLint/Prettier: Run well-optimized rules to clean up unused imports

Problem: Yarn users or legacy-peer-deps workaround needed

Solution: Taiga UI depends on many Taiga Family packages. Yarn and pnpm do not automatically install transitive peer dependencies. Manually check each Taiga UI package's package.json and install missing peer dependencies.

Problem: Cannot resolve dependency for ng-web-apis, maskito, ng-polymorpheus, or ng-event-plugins

Solution: Same as above - manually install transitive peer dependencies by checking each Taiga UI package's package.json

Problem: Cannot find module 'ts-morph' error after nx migrate --run-migrations

Solution: This is an Nx issue with the ng migrate command. Either:

• Bump Nx version, or
• Run npm install followed by re-running the migration

Problem: FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory

Solution: Migration schematics recursively traverse every file and directory, which can be memory-intensive. Increase the memory limit for the Node.js process:

NODE_OPTIONS="--max-old-space-size=4096" ng update @taiga-ui/cdk

Problem: Basic ng update / nx migrate command fails, need to execute schematics manually

Solution:

1. Manually update all Taiga UI packages to v{NEXT_MAJOR} in package.json (change versions without console commands, then run npm install)
2. Verify node_modules/@taiga-ui/cdk/package.json contains the v{NEXT_MAJOR} version
3. Execute:

Angular CLI:

ng update @taiga-ui/cdk --from=@taiga-ui/cdk@<old-version> --to=@taiga-ui/cdk@<new-version>

Nx:

nx migrate @taiga-ui/cdk --from=@taiga-ui/cdk@<old-version>
nx migrate --run-migrations=migrations.json

Documenting Uncertain or Broken Migration Points

When encountering migration issues that cannot be resolved immediately, create and maintain a dedicated file (e.g., MIGRATION_ISSUES.md or TODO_MIGRATION.md) to track all uncertain or potentially broken areas.

Two-tier Documentation Format

Quick entry (for straightforward blockers):

- [ ] `src/app/button.component.html:34` — `TuiButtonModule` TODO,
      blocked: dynamic `[appearance]` binding, need user input

Use quick entries for:

• Single-file issues with clear blocking reason
• Cases where the question to ask is obvious from the TODO
• Minor style package usage that needs user decision

Full entry (only when multiple files affected or behavior change is possible):

Use the 7-field format below for:

• Issues spanning multiple files
• Potential behavior changes
• Complex style package dependencies
• Cases requiring detailed explanation

Required Format for Full Entry

Each documented issue must include:

1. File path - Full relative path to the affected file (or list of files)
2. Line number - Exact line where the issue occurs
3. Original code - The code snippet before your attempted fix
4. Issue description - Clear explanation of what is uncertain or broken
5. Attempted solutions - What migration approaches you considered and why they may not work
6. Potential impact - What could break if the wrong fix is applied (runtime, template, styles, build)
7. Migration version - Which Taiga UI version migration this relates to (if known)

Example Full Entry Format

## Issue #<number>: <Brief description>

**Files:**

- `path/to/component.ts`
- `path/to/component.html`

**Lines:** 42, 15

**Migration:** v4 -> v5

**Original code:**

```typescript
// TODO: migrate to new button API
@Input() mode: 'accent' | 'primary' = 'primary';
```

```html
<button [mode]="mode">Click me</button>
```

**Issue:**
The old `mode` input was replaced with a new directive-based API, but this component
uses dynamic binding that may not be compatible with the new approach.

**Attempted solutions:**

- Direct replacement with `tuiAppearance` - unclear if dynamic values work
- Keeping old API temporarily - requires deprecated module import

**Potential impact:**

- Runtime error if binding fails
- Visual regression if styling is not applied correctly

Workflow Integration

1. During initial scan: Create the migration issues file at the start of the migration session
2. When blocked: Add a Quick Entry before moving to the next TODO
3. Before asking user: Reference the documented entry in your question
4. After resolution: Mark the entry as resolved with a brief note about the applied fix

Definition of Done

The migration session is complete when ALL of the following are true:

• No // TODO: (Taiga UI migration) comments remain in source files, OR each remaining TODO has a corresponding entry in MIGRATION_ISSUES.md
• No imports from @taiga-ui/legacy exist, OR each remaining import is explicitly accepted by the user
• ng build / nx build completes without errors
• No new TypeScript errors were introduced (TS6133 unused-import errors are acceptable — resolve via IDE as described in Phase 4)
• All entries in MIGRATION_ISSUES.md have been shown to the user

Do not refactor, rename, or improve code beyond what migration requires.

When to Ask the User

Use the question templates from the TODO Classification table for all TODO-related decisions.

Additionally, ask when:

• Migration schematics failed or produced unexpected errors
• The project has custom configurations that may affect migration
• Step 0 context cannot be determined automatically
• A peer-dependency conflict cannot be resolved by aligning Taiga UI package versions

What Not to Do

• Do not use --legacy-peer-deps, --force, or any flag that bypasses dependency resolution, and do not add legacy-peer-deps=true to .npmrc if it was not already there — these hide real version conflicts that will break the migration at runtime; resolve conflicts explicitly instead
• Do not hardcode a fix based only on the TODO text
• Do not delete deprecated dependencies first and discover breakage later
• Do not rewrite unrelated code while chasing a migration TODO
• Do not suppress TODOs with a new warning if the actual fix is already known and safe
• Do not continue if you cannot explain why the change is safe from the local code context
• Do not skip the prerequisites checklist - ensure environment is properly prepared
• Do not skip Step 0 (Gather Context) - know your environment before acting