Devcontainer Spec Compatibility Matrix
Compatibility of fabro-devcontainer with the devcontainer.json reference.
Legend: Yes = fully supported, Partial = parsed but incomplete, No = not supported, Planned = intended for future
General
| Property |
Status |
Notes |
name |
No |
Silently ignored by serde (unknown fields are skipped); not exposed in DevcontainerConfig |
forwardPorts |
Yes |
Numeric and string formats (e.g., "8080:80", "9090") extracted into DevcontainerConfig::forwarded_ports; merged with compose ports in compose mode |
portsAttributes |
No |
Not parsed |
otherPortsAttributes |
No |
Not parsed |
updateRemoteUserUID |
No |
Not parsed |
containerEnv |
Yes |
Baked into generated Dockerfile as ENV directives; also exposed in DevcontainerConfig::container_env |
remoteEnv |
Yes |
Merged into DevcontainerConfig::environment with variable substitution |
containerUser |
No |
Parsed but unused; not exposed in DevcontainerConfig |
remoteUser |
Yes |
Exposed as DevcontainerConfig::remote_user |
userEnvProbe |
No |
Not parsed |
overrideCommand |
No |
Parsed but unused |
shutdownAction |
No |
Not parsed |
Image
| Property |
Status |
Notes |
image |
Yes |
Used as FROM line when no Dockerfile is specified; defaults to mcr.microsoft.com/devcontainers/base:ubuntu |
Build (Dockerfile)
| Property |
Status |
Notes |
build.dockerfile |
Yes |
Resolved relative to devcontainer.json; content read and used as base Dockerfile |
build.context |
Yes |
Resolved with variable substitution; passed as DevcontainerConfig::build_context |
build.args |
Yes |
Parsed and exposed in DevcontainerConfig::build_args for passing to docker build --build-arg |
build.target |
Yes |
Parsed with variable substitution; exposed as DevcontainerConfig::build_target for passing to docker build --target |
build.cacheFrom |
No |
Not parsed |
build.options |
No |
Not parsed |
Compose
| Property |
Status |
Notes |
dockerComposeFile |
Yes |
Single path and array of paths supported; multiple files are merged (last wins for image/build/user; ports accumulate; environment overrides) |
service |
Yes |
Required when dockerComposeFile is set; used to extract service config |
runServices |
No |
Not parsed; all services assumed |
shutdownAction |
No |
Not parsed |
overrideCommand |
No |
Parsed but unused |
workspaceFolder |
Yes |
Defaults to /workspaces/{repo-name} |
workspaceMount |
No |
Parsed but unused |
Features
| Property |
Status |
Notes |
features |
Yes |
Fetched via oras CLI (OCI refs), local path copy (.//../), or HTTPS download. Topologically sorted by installsAfter and dependsOn. Dockerfile layers generated with options as env vars |
features (reference types) |
Yes |
OCI registry refs (default), local paths (./feature), and HTTPS URLs (https://...feature.tgz) |
Feature dependsOn |
Yes |
Hard dependencies auto-installed if missing; used for topological ordering alongside installsAfter |
Feature containerEnv |
Yes |
Collected from each feature in install order; merged with devcontainer.json containerEnv (devcontainer.json wins on conflicts) |
Feature onCreateCommand |
Yes |
Collected in install order and appended after devcontainer.json onCreateCommand |
Feature postCreateCommand |
Yes |
Collected in install order and appended after devcontainer.json postCreateCommand |
Feature postStartCommand |
Yes |
Collected in install order and appended after devcontainer.json postStartCommand |
overrideFeatureInstallOrder |
No |
Not parsed |
Lifecycle
| Property |
Status |
Notes |
initializeCommand |
Yes |
All three forms supported: string, array, object (parallel). Exposed as DevcontainerConfig::initialize_commands |
onCreateCommand |
Yes |
All three forms supported. Exposed as DevcontainerConfig::on_create_commands |
updateContentCommand |
No |
Not parsed |
postCreateCommand |
Yes |
All three forms supported. Exposed as DevcontainerConfig::post_create_commands |
postStartCommand |
Yes |
All three forms supported. Exposed as DevcontainerConfig::post_start_commands |
postAttachCommand |
No |
Not parsed |
waitFor |
No |
Not parsed |
Host
| Property |
Status |
Notes |
hostRequirements |
No |
Not parsed |
init |
No |
Not parsed |
privileged |
No |
Not parsed |
capAdd |
No |
Not parsed |
securityOpt |
No |
Not parsed |
mounts |
No |
Not parsed |
gpuRequest |
No |
Not parsed |
Customizations
| Property |
Status |
Notes |
customizations |
No |
Unknown fields are silently ignored by serde, so customizations is accepted but not processed |
Variables
| Variable |
Status |
Notes |
${localWorkspaceFolder} |
Yes |
Substituted via VariableContext |
${localWorkspaceFolderBasename} |
Yes |
Substituted via VariableContext |
${containerWorkspaceFolder} |
Yes |
Substituted via VariableContext |
${containerWorkspaceFolderBasename} |
Yes |
Derived from containerWorkspaceFolder by splitting on / |
${localEnv:VAR} |
Yes |
Reads from host environment; supports :default syntax |
${containerEnv:VAR} |
No |
Not implemented (requires running container) |
${devcontainerId} |
No |
Not implemented |
JSONC Support
The parser supports JSONC (JSON with Comments):
- Line comments (
//)
- Block comments (
/* */)
- Trailing commas before
} and ]
File Discovery
Searched in order:
<path>/.devcontainer/devcontainer.json<path>/.devcontainer.json- Direct path if it ends in
devcontainer.json
- Subdirectory format:
<path>/.devcontainer/<subdir>/devcontainer.json — subdirectories sorted alphabetically, first match used
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