codex/codex-rs/config/src/loader

codex-config loader

This module is the canonical place to load and describe Codex configuration layers (user config, CLI/session overrides, cloud-managed config, managed config, and MDM-managed preferences) and to produce:

• An effective merged TOML config.
• Per-key origins metadata (which layer “wins” for a given key).
• Per-layer versions (stable fingerprints) used for optimistic concurrency / conflict detection.

Public surface

Exported from codex_config::loader:

• load_config_layers_state(fs, codex_home, cwd_opt, cli_overrides, options, thread_config_loader) -> ConfigLayerStack
• ConfigLayerStack
  • effective_config() -> toml::Value
  • origins() -> HashMap<String, ConfigLayerMetadata>
  • layers_high_to_low() -> impl Iterator<Item = &ConfigLayerEntry>
  • with_user_config(user_config) -> ConfigLayerStack
• ConfigLayerEntry (one layer’s {name, config, version, disabled_reason}; name carries source metadata)
• ConfigLoadOptions (user-facing load behavior such as strict config validation)
• LoaderOverrides (test/override hooks for managed config sources)
• merge_toml_values(base, overlay) (public helper used elsewhere)

Layering model

Precedence is top overrides bottom:

1. LegacyManagedConfigTomlFromMdm (MDM-delivered managed_config.toml, while it is being phased out)
2. LegacyManagedConfigTomlFromFile (managed_config.toml, while it is being phased out)
3. SessionFlags (CLI overrides, applied as dotted-path TOML writes)
4. Project config (.codex/config.toml)
5. User profile config, when present
6. User config (config.toml)
7. EnterpriseManaged cloud-managed config bundle layers
8. System config (/etc/codex/config.toml or the Windows system config path)

ConfigLayerStack stores layers in the opposite order internally: lowest precedence first, highest precedence last, so later layers override earlier layers when folded. Thread config entries supplied by thread_config_loader are inserted according to their translated ConfigLayerSource precedence.

Layers with a disabled_reason are still surfaced for UI, but are ignored when computing the effective config and origins metadata. This is what ConfigLayerStack::effective_config() implements.

Typical usage

Most callers want the effective config plus metadata:

use codex_config::LoaderOverrides;
use codex_config::NoopThreadConfigLoader;
use codex_config::loader::load_config_layers_state;
use codex_exec_server::LOCAL_FS;
use codex_utils_absolute_path::AbsolutePathBuf;
use toml::Value as TomlValue;

let cli_overrides: Vec<(String, TomlValue)> = Vec::new();
let cwd = AbsolutePathBuf::current_dir()?;
let layers = load_config_layers_state(
    LOCAL_FS.as_ref(),
    &codex_home,
    Some(cwd),
    &cli_overrides,
    LoaderOverrides::default(),
    &NoopThreadConfigLoader,
).await?;

let effective = layers.effective_config();
let origins = layers.origins();
let layers_for_ui = layers.layers_high_to_low().collect::<Vec<_>>();

Internal layout

Implementation is split by concern:

• state.rs: public types (ConfigLayerEntry, ConfigLayerStack) + merge/origins convenience methods.
• layer_io.rs: reading config.toml, managed config, and managed preferences inputs.
• overrides.rs: CLI dotted-path overrides → TOML “session flags” layer.
• merge.rs: recursive TOML merge.
• fingerprint.rs: stable per-layer hashing and per-key origins traversal.
• macos.rs: managed preferences integration (macOS only).