COBOL Offset Analyzer

A VSCode extension that analyzes COBOL data structures and displays the offset (starting position) and length of each variable in bytes using hover tooltips.

✨ Features

• 🟢 Auto-Active by Default - Starts active when installed, no setup needed
• 📍 Automatic Offset Calculation - Hover over any COBOL variable to see position and length
• 📏 Shows Length in Bytes - Display format: Position and Length in NNNNNN format
• 🎯 Type Detection - Identifies Numeric, Alphanumeric, COMP, COMP-3, Group/Structure, etc.
• 💾 Persistent State - Remembers if extension is active/inactive between sessions
• 🔄 Toggle On/Off - Easy enable/disable with Ctrl+Shift+O or status bar click
• ✅ Supports All COBOL Features:
  • PIC clause length calculation
  • COMP and COMP-3 numeric formats
  • OCCURS clause for arrays
  • REDEFINES clause (correctly excludes redefined bytes)
  • SYNCHRONIZED fields
  • Nested groups and subgroups

Supported File Extensions

• .cbl - COBOL source files
• .cob - COBOL source files
• .cobol - COBOL source files

How to Use

1. Open a COBOL File

Open any .cbl, .cob, or .cobol file in VSCode. The extension is ACTIVE by default.

2. Hover Over Variables

Simply hover your mouse over any variable or group header to see:

Position:   000001
Length:     000005 bytes
Type:       Numeric

3. Status Indicator

Look at the bottom-right corner of VSCode (status bar):

• ✅ COBOL Offset: ON - Extension is active
• ❌ COBOL Offset: OFF - Extension is inactive

Click it to toggle, or press Ctrl+Shift+O (Mac: Cmd+Shift+O)

4. Deactivate/Reactivate

Press Ctrl+Shift+O (or Cmd+Shift+O on Mac) to:

• Disable the extension (status shows RED ❌)
• Re-enable the extension (status shows GREEN ✅)

The state is saved and persists between sessions.

Example

When you hover over a COBOL variable:

01  EMPLOYEE-RECORD.
    05  EMP-ID              PIC 9(5).
    05  EMP-NAME            PIC X(30).
    05  EMP-SALARY          PIC 9(7)V99 COMP-3.
    05  EMP-HIRE-DATE.
        10  EMP-HIRE-YEAR   PIC 9(4).
        10  EMP-HIRE-MONTH  PIC 9(2).
        10  EMP-HIRE-DAY    PIC 9(2).
    05  EMP-STATUS          PIC X(1).

Hover Information:

• EMP-ID: Position 000001, Length 000005 bytes, Type: Numeric
• EMP-NAME: Position 000006, Length 000030 bytes, Type: Alphanumeric
• EMP-SALARY: Position 000036, Length 000005 bytes, Type: COMP-3 (Packed Decimal)
• EMP-HIRE-DATE: Position 000041, Length 000008 bytes, Type: Group/Structure
• EMP-HIRE-YEAR: Position 000041, Length 000004 bytes, Type: Numeric
• EMP-HIRE-MONTH: Position 000045, Length 000002 bytes, Type: Numeric
• EMP-HIRE-DAY: Position 000047, Length 000002 bytes, Type: Numeric
• EMP-STATUS: Position 000049, Length 000001 bytes, Type: Alphanumeric

Commands

Testing

A sample COBOL file is included (sample.cbl). To test:

1. Open sample.cbl
2. Hover over any variable
3. See the offset/length information in the tooltip

Unit Tests

Test individual PIC clause calculations:

node test-calculations.js

Test complete COBOL structure parsing:

node test-structure.js

Test REDEFINES handling:

node test-redefines-validation.js

Development

Build from Source

npm install
npm run compile

Watch for Changes

npm run watch

Debug in VSCode

1. Press F5 to start debugging
2. A new VSCode window opens with your extension loaded
3. Open a COBOL file and test the hover functionality

Original Algorithm

This extension implements the same offset-calculation algorithm that has been running successfully on IBM Mainframe z/OS (REXX) for 20+ years. The logic is based on the proven REXX implementation and has been adapted for VSCode.

License

MIT