Nomos Compilation Debugging

This skill provides a systematic approach to debugging Nomos compilation failures, from provider issues to reference resolution errors.

When to Use This Skill

• nomos build command fails with errors
• Provider-related failures (not found, connection refused)
• Reference resolution errors (unresolved reference)
• Import cycle detection failures
• Unexpected compilation output or determinism issues
• Provider initialization or fetch errors

Diagnostic Process

Follow these steps in order for systematic troubleshooting:

Step 1: Identify Error Category

Compilation errors fall into these categories:

1. Provider Errors - Provider binary issues, connection failures
2. Reference Errors - Unresolved references, invalid paths
3. Import Errors - Cycle detection, missing imports, parse failures
4. Syntax Errors - Invalid .csl syntax
5. Configuration Errors - Missing lockfile, invalid provider config
6. Determinism Issues - Non-reproducible builds

Step 2: Check Provider Configuration

Verify Lockfile Exists

# Check for providers lockfile
ls -la .nomos/providers.lock.json

# If missing, run init:
nomos init config.csl

Expected lockfile structure:

{
  "providers": [
    {
      "alias": "configs",
      "type": "file",
      "version": "0.2.0",
      "os": "darwin",
      "arch": "arm64",
      "path": ".nomos/providers/file/0.2.0/darwin-arm64/provider",
      "checksum": "sha256:..."
    }
  ]
}

Verify Provider Binaries Installed

# Check provider directory structure
find .nomos/providers -type f -name "provider"

# Expected structure:
# .nomos/
#   providers/
#     file/
#       0.2.0/
#         darwin-arm64/
#           provider         # Must be executable

# Verify binary is executable
ls -l .nomos/providers/file/0.2.0/darwin-arm64/provider
# Should show: -rwxr-xr-x (executable flag)

# If not executable:
chmod +x .nomos/providers/file/0.2.0/darwin-arm64/provider

Test Provider Binary Manually

# Run provider directly - should print PORT
.nomos/providers/file/0.2.0/darwin-arm64/provider
# Expected output: PORT=<number>

# If it crashes or prints errors, provider is broken
# Solution: Re-download with nomos init --force

Step 3: Debug Provider Connection Failures

Symptom: failed to start provider or connection refused

Check Provider Startup

# Enable verbose logging if available
# Run build with provider debugging
nomos build config.csl 2>&1 | tee build.log

# Look for:
# - "Starting provider: <alias>"
# - "Provider port: <port>"
# - Connection errors

Verify Provider Protocol

Provider must:

1. Listen on 127.0.0.1 (localhost only)
2. Print PORT=<number> to stdout
3. Start gRPC server before returning
4. Implement all required RPCs (Init, Fetch, Info, Health, Shutdown)

Test with minimal config:

source:
  alias: 'test'
  type: 'autonomous-bits/nomos-provider-file'
  version: '0.2.0'

Step 4: Debug Reference Resolution Errors

Symptom: unresolved reference: reference:alias:path

Verify Source Declaration

Check that provider alias is declared:

source:
  alias: 'configs'  # Must match reference alias
  type: 'autonomous-bits/nomos-provider-file'
  version: '0.2.0'

app:
  name: reference:configs:app.name  # Alias must match

Verify Reference Path Exists

Test provider Fetch manually if possible:

# For file provider, verify file exists
ls -la ./data/app.name  # or whatever the file path should be

Check Provider Init Configuration

Ensure provider receives correct configuration:

source:
  alias: 'configs'
  type: 'autonomous-bits/nomos-provider-file'
  version: '0.2.0'
  directory: './data'  # Provider-specific config

Common Issues:

• Missing required config fields (e.g., directory for file provider)
• Incorrect config types (string vs number)
• Relative paths that don't resolve correctly

Enable AllowMissingProvider Mode

For debugging, continue compilation without provider:

# This will show warnings but not fail
nomos build --allow-missing-provider config.csl

Step 5: Debug Import Errors

Symptom: cycle detected or failed to resolve import

Check Import Statements

Verify import syntax:

import:base:./base.csl  # Correct format: import:<alias>:<path>

Detect Import Cycles

A imports B
B imports C
C imports A  ← Cycle!

Solution: Refactor to break cycle

• Extract shared config to separate file
• Remove circular dependencies
• Use references instead of imports where possible

Verify Import Paths

# Check that imported files exist
ls -la ./base.csl
ls -la ./shared/common.csl

# Verify paths are relative to importing file or absolute

Step 6: Debug Syntax Errors

Symptom: Parse errors with line/column numbers

Read Error Messages Carefully

Parser errors show:

config.csl:15:3: SyntaxError: expected ':' after key

Location format: <file>:<line>:<column>

Common Syntax Mistakes

1. Missing colons:

   nomosCopy

   # ❌ Wrong
   database
     host: localhost
   
   # ✅ Correct
   database:
     host: localhost
   

2. Invalid reference syntax:

   nomosCopy

   # ❌ Wrong
   app: reference:configs.app.name
   
   # ✅ Correct
   app: reference:configs:app.name
   

3. Empty source alias:

   nomosCopy

   # ❌ Wrong
   source:
     alias: ''
   
   # ✅ Correct
   source:
     alias: 'myalias'
   

Step 7: Debug Determinism Issues

Symptom: Same input produces different output on repeated builds

Test Reproducibility

# Build twice and compare
nomos build config.csl -o output1.json
nomos build config.csl -o output2.json
diff output1.json output2.json

# Should be identical (exit code 0)

Common Causes

1. Provider non-determinism: Provider returns different data

   • Solution: Fix provider to be deterministic or use caching

2. Timestamp injection: Metadata includes timestamps

   • Solution: Remove timestamps or make them optional

3. Map iteration order: Go maps iterate in random order

   • Solution: Sort keys before serialization (compiler does this)

4. Concurrent provider fetches: Race conditions

   • Solution: Enable provider caching (compiler does this)

Verify File Order

Nomos processes files in lexicographic order (UTF-8):

# Check file discovery order
find . -name "*.csl" -type f | sort

# Should match compilation order in build output

Step 8: Check Configuration Merge Behavior

Symptom: Unexpected values in final output

Understand Merge Semantics

Nomos deep-merge rules:

• Maps: Recursive merge, combining keys
• Scalars: Last-wins (newer value replaces older)
• Arrays: Last-wins (entire array replaced)

# base.csl
database:
  host: localhost
  port: 5432

# override.csl
import:base:./base.csl
database:
  host: prod-server  # Overrides localhost
  # port: 5432 preserved from base

Trace Value Provenance

Enable metadata tracking if available to see where values came from.

Step 9: Verify Platform-Specific Issues

Symptom: Works on one OS/arch but not another

Check Provider Platform

Provider binaries are platform-specific:

# Verify correct binary for your platform
uname -sm
# Darwin arm64 → darwin-arm64
# Linux x86_64 → linux-amd64

# Check lockfile matches:
cat .nomos/providers.lock.json | grep -A 5 '"os"'

Cross-Platform Installation

Install providers for different platforms:

# Install for Linux on macOS development machine
nomos init --os linux --arch amd64 config.csl

# Then push .nomos/ directory to Linux CI

Common Error Messages and Solutions

"provider binary not found"

Cause: Provider not installed or wrong path in lockfile

Solution:

nomos init --force config.csl  # Re-download

"connection refused"

Cause: Provider failed to start or wrong port

Solution:

1. Test provider manually: .nomos/providers/.../provider
2. Check provider prints PORT=<number>
3. Verify provider doesn't exit immediately

"unresolved reference"

Cause: Reference path doesn't exist in provider data

Solution:

1. Verify source alias matches reference
2. Check provider configuration (e.g., directory path)
3. Test provider data manually
4. Use --allow-missing-provider to debug

"cycle detected"

Cause: Circular import chain

Solution:

1. Map import chain: A → B → C → A
2. Extract shared config to break cycle
3. Use references instead of imports

"invalid checksum"

Cause: Provider binary modified or corrupted

Solution:

# Re-download provider
nomos init --force config.csl

# Or manually verify checksum
shasum -a 256 .nomos/providers/.../provider
# Compare with lockfile checksum

Advanced Debugging

Enable Verbose Logging

If Nomos supports verbose mode:

nomos build -v config.csl       # Verbose output
nomos build -vv config.csl      # Very verbose (debug level)

Inspect Provider gRPC Communication

Use gRPC debugging tools if needed:

# Find provider port
ps aux | grep provider

# Connect with grpcurl (if provider running)
grpcurl -plaintext localhost:<port> list
grpcurl -plaintext localhost:<port> nomos.provider.v1.ProviderService/Info

Test Components Individually

1. Parse only: Verify .csl syntax
2. Init only: Test provider installation
3. Build without providers: Use --allow-missing-provider
4. Build single file: Isolate problematic config

Prevention Best Practices

1. Commit lockfile: Check .nomos/providers.lock.json into git
2. Pin versions: Use explicit version in source declarations
3. Test providers: Verify provider works before using in config
4. Validate syntax: Use editor tooling for .csl files
5. Run CI builds: Catch determinism issues early
6. Document references: Comment expected provider data structure

Reference Documentation

For more details, see:

• Nomos CLI Documentation
• Compiler Library Documentation
• Provider Authoring Guide
• External Providers Architecture