Add Elsa Script DSL

[sfmskywalker]

Description

This PR introduces ElsaScript, a JavaScript-inspired textual Domain Specific Language (DSL) for authoring Elsa 3 workflows.

While the visual designer remains excellent for high-level composition and non-technical users, a textual DSL fills a critical gap for developers who need speed, precision, and better integration with source control workflows.

Motivation & Rationale

Why introduce a textual DSL when we already have JSON/YAML and a visual designer?

1. Superior Source Control & Code Reviews

   • The Problem: Reviewing changes in large JSON/YAML workflow definitions is difficult. Diffs are often noisy, formatting-dependent, and semantically opaque.
   • The Solution: ElsaScript provides a concise, human-readable format. PR reviews become meaningful because the logic is visible, not buried in serialization syntax. Merge conflicts become standard code conflicts, which are easier to resolve.

2. Developer Productivity

   • The Problem: For developers, "drag-and-drop" can be slower than typing, especially when defining variables, loops, and complex conditional logic.
   • The Solution: ElsaScript allows developers to author workflows at the speed of typing. Refactoring (e.g., renaming a variable across a workflow) becomes a simple Find & Replace operation.

3. Runtime Flexibility with "Compiled" Safety

   • ElsaScript compiles directly to the Elsa 3 Workflow object model at runtime. This allows workflows to be loaded dynamically from Blob Storage or databases (like scripts) without requiring a full project recompile/redeployment (unlike C# workflows), while offering a much terser syntax than raw JSON.

4. Expressive Logic

   • The DSL supports high-level constructs like flowchart, for loops, if/else blocks, and switch statements that map 1:1 to their Activity counterparts. It also supports mixed expression languages (JavaScript, C#, Liquid) within the same file.

Key Features

• Hybrid Syntax: Familiar C# and JavaScript-like syntax for defining variables (var, const) and control flow.
• Flowchart Support: First-class support for defining graph-based logic using text (nodes, connections, entry points).
• Metadata Support: Define workflow properties (DefinitionId, Version, Description) directly in the header.
• Activity Discovery: Dynamically resolves activities from the registry, supporting both built-in and custom activities.
• Performance: Includes optimizations for Blob Storage providers to filter files by extension before parsing.

Example

A simple workflow demonstrating loops, mixed expression languages (JS and C#), and variable scoping:

use expressions js;

workflow ForLoopTest 
{
    WriteLine("First loop");

    // Range-based loop with JavaScript expression interpolation
    for (var i = 0 through 10 step 1)
    {
        WriteLine(js => `Step: ${variables.i}`);
    }

    WriteLine("Second loop");

    // Range-based loop reusing variable with C# expression
    for (var i = 0 to 10 step 2)
      WriteLine(cs => return $"Step: {Variables.Get("i")}";);
  
    WriteLine("Done!");
}

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Reset default expression language per compilation

ElsaScriptCompiler stores the default expression language in _defaultExpressionLanguage and mutates it when a use expressions directive is parsed, but CompileWorkflowNodeAsync never reinitializes the field for a new compilation. Because the compiler is registered as a scoped service and reused, compiling a workflow after one that set use expressions liquid will keep Liquid as the default even if the later workflow omits that directive, so unqualified expressions get compiled in the wrong language. Reset the default before processing each workflow to avoid leaking state across compilations.

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[Copilot]

Pull Request Overview

This PR introduces ElsaScript, a JavaScript-inspired textual DSL for authoring Elsa 3 workflows, providing a code-centric alternative to C# WorkflowBuilder APIs and JSON workflow definitions.

Key changes include:

• New ElsaScript parser and compiler using Parlot for robust parsing
• AST-based workflow compilation with support for variables, control flow, and flowcharts
• Integration with BlobStorage provider for .elsa file support
• Database schema updates to support symmetric round-trip preservation of original source
• Refactored activity instantiation to remove dependency on IActivityFactory

Reviewed Changes

Copilot reviewed 105 out of 108 changed files in this pull request and generated 33 comments.

Show a summary per file

File	Description
src/modules/Elsa.Dsl.ElsaScript/	New module implementing ElsaScript parser, compiler, AST nodes, and materializer
src/modules/Elsa.WorkflowProviders.BlobStorage.ElsaScript/	BlobStorage integration for ElsaScript workflows
src/modules/Elsa.Workflows.Core/Models/ActivityConstructorContext.cs	Refactored from interface-based to factory-based activity instantiation
src/modules/Elsa.Workflows.Management/Entities/WorkflowDefinition.cs	Added OriginalSource field for symmetric round-trip support
test/integration/Elsa.Dsl.ElsaScript.IntegrationTests/	Comprehensive parser and compiler integration tests
Database migrations	Added OriginalSource column across all EF Core providers
src/modules/Elsa.Scheduling/Services/LocalScheduler.cs	Fixed race conditions by using ConcurrentDictionary

Files not reviewed (2)

• src/modules/Elsa.Persistence.EFCore.SqlServer/Migrations/Management/20251116182628_V3_6.Designer.cs: Language not supported
• src/modules/Elsa.Persistence.EFCore.Sqlite/Migrations/Management/20251116182711_V3_6.Designer.cs: Language not supported

Comments suppressed due to low confidence (4)

src/modules/Elsa.Persistence.EFCore.PostgreSql/Migrations/Management/20251116182753_V3_6.cs:30

• The migration adds the OriginalSource column, then performs ALTER TABLE operations, and finally drops the OriginalSource column in the same Up() method. This will remove the column that was just added. The DropColumn should only be in the Down() method for rollback.
  src/modules/Elsa.Workflows.Management/Extensions/ActivityFactoryExtensions.cs:1
• The entire ActivityFactoryExtensions.cs file has been deleted, but references to this extension method may still exist elsewhere in the codebase if it was used. Ensure that all usages of the Create<T>() extension method have been updated to use the new pattern.
  test-flowchart.txt:1
• Test files test-flowchart.txt and test-simple-flowchart.elsa appear to be temporary test artifacts that should not be committed to the repository root. Consider moving them to a test fixtures directory or adding them to .gitignore.
  src/modules/Elsa.Workflows.Core/Models/ActivityConstructorContext.cs:62
• Both branches of this 'if' statement write to the same variable - consider using '?' to express intent better.

[Copilot]

Using NCLOB for OriginalSource in Oracle may cause performance issues for large workflow definitions. The ModelSnapshot shows NVARCHAR2(2000) instead. Consider using CLOB or ensure consistency between migration and snapshot, or document the size limitation if NVARCHAR2(2000) is intentional.

[sfmskywalker]

@copilot open a new pull request to apply changes based on this feedback. Use the recommended solution, keeping in mind that OriginalSource may exceed the 2000 character limit, given that it may store large workflow definitions in JSON format.

[Copilot]

Using System.Diagnostics.Debug.WriteLine for production diagnostics is not recommended. This output will only appear in debug builds and won't be visible in production logs. Use the ILogger infrastructure instead for consistent logging across environments.

[sfmskywalker]

@copilot open a new pull request to apply changes based on this feedback. Find all occurrences of System.Diagnostics.Debug.WriteLine and replace them appropriately with the ILogger infrastructure.

[Copilot]

Both branches of this 'if' statement write to the same variable - consider using '?' to express intent better.

[Copilot]

Both branches of this 'if' statement write to the same variable - consider using '?' to express intent better.

[Copilot]

Both branches of this 'if' statement write to the same variable - consider using '?' to express intent better.

[Copilot]

@sfmskywalker I've opened a new pull request, #7079, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@sfmskywalker I've opened a new pull request, #7080, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@sfmskywalker I've opened a new pull request, #7081, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@sfmskywalker I've opened a new pull request, #7082, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

@sfmskywalker I've opened a new pull request, #7083, to work on those changes. Once the pull request is ready, I'll request review from you.