Add Eclipse 4 Commands documentation and migration guide

[Copilot]

Overview

Adds comprehensive documentation for calling commands programmatically in Eclipse 4 (E4) applications and migrating from Eclipse 3.x command execution patterns.

Changes

New Documentation: docs/Eclipse4_Commands.md

Created a complete guide for programmatically calling commands in E4 applications, covering:

• ECommandService and EHandlerService usage
• Basic command execution without parameters
• Command execution with parameters using Map<String, Object>
• Dependency injection patterns for parts and handlers
• Complete working examples with SWT UI integration
• Error handling and exception management
• Common use cases (opening views, perspectives, saving files, etc.)
• Required MANIFEST.MF dependencies
• Key differences from Eclipse 3.x approach

All code examples are based on actual Eclipse Platform UI source code (e.g., PerspectiveSwitcher.java, LegacyHandlerService.java) to ensure technical accuracy.

Example from the new documentation:

@Inject
private ECommandService commandService;

@Inject
private EHandlerService handlerService;

public void showSpecificView(String viewId) {
    Map<String, Object> parameters = new HashMap<>();
    parameters.put("org.eclipse.ui.views.showView.viewId", viewId);
    
    ParameterizedCommand command = commandService.createCommand(
        "org.eclipse.ui.views.showView", 
        parameters
    );
    
    handlerService.executeHandler(command);
}

Enhanced Migration Guide: docs/Eclipse4_Migration.md

Added a new section "Migrate Programmatic Command Execution" that provides:

• Side-by-side E3 vs E4 code examples
• Step-by-step migration instructions
• Comparison table highlighting key differences (service names, method names, parameter formats)
• Migration patterns for common scenarios (opening views, saving, etc.)
• Updated common pitfalls section with command-specific gotchas

E3 to E4 Migration Example:

Aspect	Eclipse 3.x	Eclipse 4.x
Command Service	ICommandService	ECommandService
Handler Service	IHandlerService	EHandlerService
Service Access	getSite().getService()	@Inject annotation
Command Creation	getCommand() + new ParameterizedCommand()	createCommand()
Parameter Format	Parameterization[] array	Map<String, Object>
Execution Method	executeCommand()	executeHandler()

Cross-References Added

• Added prominent reference in docs/Eclipse4_RCP_FAQ.md (Commands and Handlers section)
• Added reference in docs/Eclipse4_RCP_EAS_List_of_All_Provided_Services.md
• Bidirectional links between Eclipse4_Commands.md and Eclipse4_Migration.md
• Links to related documentation (Platform Command Framework, RCP FAQ, Dependency Injection)

Motivation

As noted in the issue, Eclipse Platform UI was missing clear documentation on how to programmatically call commands using the E4 approach. Developers needed guidance on:

1. Using ECommandService and EHandlerService instead of the E3 services
2. Migrating existing E3 command execution code to E4
3. Understanding parameter handling differences between E3 and E4

This documentation provides developers with practical, copy-paste ready examples and comprehensive migration guidance.

References

• Vogella tutorial: https://www.vogella.com/tutorials/Eclipse4Services/article.html#command-and-handler-service
• Based on actual Platform UI source code patterns

Fixes eclipse-platform/eclipse.platform.ui#XXXX

Original prompt

Describe ho Commands are called in E4 and update the migration guide.

Currently we missing a description on how to call Commands using the E4 way

For this we want:

• a new docs/Eclipse4_Commands.md describing how one calls a command, see for example here https://www.vogella.com/tutorials/Eclipse4Services/article.html#command-and-handler-service but the source code should have examples too.
• adjust the Eclipse4_Migration.md to add a section how to migrate from programatically calling commands from using ICommandService (e3) to ECommandService(e4)

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[laeubi]

Looks like a good starting point

[laeubi]

Build will not test documentation changes, @vogella @opcoach @ruspl-afed please suggest further enhancements in separate PRs!