GN Scope Skill

Fixes GN build file errors related to undefined variables or scope issues.

Detection Patterns

• Undefined identifier
• Assignment had no effect
• Can't load buildconfig
• Unknown variable

Strategy

1. Identify Variable: Find the undefined or misused variable.
2. Check Scope: Determine if it's a scope or declaration issue.
3. Fix Definition: Add declaration or fix scope reference.

Instructions

Step 1: Parse the Error

From: Undefined identifier: mysources Variable: mysources

Step 2: Common Fixes

Undefined variable - add declaration:

# Before
sources = my_sources  # ERROR: undefined

# After
my_sources = [ "main.cpp" ]
sources = my_sources

Using variable before definition:

# Before (error)
executable("app") {
  sources = common_sources  # ERROR
}
common_sources = [ "util.cpp" ]

# After (move declaration up)
common_sources = [ "util.cpp" ]
executable("app") {
  sources = common_sources
}

Scope issue with inner blocks:

# Variables defined in if blocks may not be visible outside
if (is_debug) {
  debug_flags = [ "-g" ]
}
# debug_flags might be undefined here if is_debug is false

Step 3: GN Best Practices

• Declare variables before use
• Use defined() to check optional variables
• Import shared configs with import("path")