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skills/rails-version-detector/SKILL.md

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+# Rails Version Detector
+
+---
+name: rails-version-detector
+description: Detects Rails version from project files (Gemfile.lock, Gemfile, or .ruby-version)
+version: 1.1.0
+author: Rails Workflow Team
+tags: [rails, version, detection, helper]
+priority: 2
+---
+
+## Purpose
+
+Automatically detects the Rails version in the current project by inspecting:
+1. `Gemfile.lock` (preferred - exact version)
+2. `Gemfile` (fallback - version constraint)
+3. `.ruby-version` or `.tool-versions` (Ruby version hint)
+
+Returns version information for use by other skills and agents.
+
+## Usage
+
+This skill is **auto-invoked** by other Rails skills when they need version information.
+
+**Manual invocation** (rarely needed):
+```
+@rails-version-detector
+```
+
+## Detection Strategy
+
+### Priority 1: Gemfile.lock (Exact Version)
+```ruby
+# Searches for:
+rails (7.1.3)
+  actioncable (= 7.1.3)
+  actionmailbox (= 7.1.3)
+  ...
+```
+
+**Extraction logic**:
+- Pattern: `rails \((\d+\.\d+\.\d+)\)`
+- Returns: Exact version (e.g., "7.1.3")
+
+### Priority 2: Gemfile (Version Constraint)
+```ruby
+# Searches for:
+gem "rails", "~> 7.1.0"
+gem 'rails', '>= 7.0.0', '< 8.0'
+```
+
+**Extraction logic**:
+- Pattern: `gem ['"]rails['"],\s*['"]([^'"]+)['"]`
+- Returns: Version constraint (e.g., "~> 7.1.0")
+- Interprets: "~> 7.1.0" → "7.1.x"
+
+### Priority 3: Ruby Version (Heuristic)
+```ruby
+# .ruby-version or .tool-versions
+ruby 3.2.2
+```
+
+**Mapping**:
+- Ruby 3.3.x → Rails 7.1+ or 8.0+
+- Ruby 3.2.x → Rails 7.0+
+- Ruby 3.1.x → Rails 7.0+
+- Ruby 3.0.x → Rails 6.1+ or 7.0
+- Ruby 2.7.x → Rails 6.0 or 6.1
+
+**Returns**: Estimated range (e.g., "7.0 or 7.1")
+
+## Output Format
+
+### Success Response
+```json
+{
+  "version": "7.1.3",
+  "source": "Gemfile.lock",
+  "confidence": "exact",
+  "major": 7,
+  "minor": 1,
+  "patch": 3
+}
+```
+
+### Constraint Response
+```json
+{
+  "version": "~> 7.1.0",
+  "source": "Gemfile",
+  "confidence": "constraint",
+  "interpreted_as": "7.1.x",
+  "major": 7,
+  "minor": 1
+}
+```
+
+### Heuristic Response
+```json
+{
+  "version": "7.0-7.1",
+  "source": ".ruby-version",
+  "confidence": "heuristic",
+  "ruby_version": "3.2.2",
+  "possible_rails": ["7.0", "7.1"]
+}
+```
+
+### Not Found Response
+```json
+{
+  "version": null,
+  "source": null,
+  "confidence": "none",
+  "error": "No Rails version detected. Is this a Rails project?"
+}
+```
+
+## Implementation
+
+**Tool usage**:
+- `Read` tool to read Gemfile.lock, Gemfile, .ruby-version
+- `Grep` tool to search for version patterns
+- Fallback to `Bash` if needed: `bundle show rails | grep 'rails-'`
+
+**Caching**:
+- Version detection results cached for session
+- Re-check if Gemfile.lock modified (check mtime)
+
+## Error Handling
+
+**Gemfile.lock missing**:
+- Fallback to Gemfile
+- Warn: "Gemfile.lock not found. Run `bundle install` for exact version."
+
+**No version found**:
+- Return error response
+- Suggest: "Ensure `gem 'rails'` in Gemfile"
+
+**Multiple Rails versions**:
+- Return first match (main Rails gem)
+- Ignore: railties, actionpack (these are sub-gems)
+
+## Integration
+
+**Auto-invoked by**:
+- @rails-docs-search (to fetch correct version docs)
+- @rails-api-lookup (to search version-specific APIs)
+- @rails-pattern-finder (to find version-appropriate patterns)
+- All 7 Rails agents (to ensure version-compatible code generation)
+
+**Manual use case**:
+```
+User: "What Rails version is this project using?"
+Assistant: *invokes @rails-version-detector*
+          "This project uses Rails 7.1.3 (detected from Gemfile.lock)"
+```
+
+## Testing
+
+**Test cases**:
+1. Rails 7.1.3 in Gemfile.lock → Exact version
+2. `~> 7.1.0` in Gemfile → Interpreted as 7.1.x
+3. Ruby 3.2.2 only → Heuristic: 7.0-7.1
+4. No Rails → Error response
+5. Rails 8.0.0 → Correct major version detection
+
+## Notes
+
+- This skill replaces the need for `mcp__rails__get_rails_info` MCP tool
+- Version detection is fast (< 1 second)
+- Results cached per session to avoid repeated file reads
+- Confidence levels help downstream skills decide if they need clarification from user