Add option to output json schema

Cargo.toml

@@ -31,6 +31,7 @@ flume = "0.11.0"
 log = "0.4.20"
 num_cpus = "1.16.0"
 rayon = "1.8.1"
+schemars = "0.8.16"
 serde = { version = "1.0.196", features = ["derive"] }
 serde_json = "1.0.113"
 shell-escape = "0.1.5"

src/main.rs

@@ -46,6 +46,10 @@ struct Args {
     #[command(flatten)]
     verbose: clap_verbosity_flag::Verbosity,
 
+    /// Output the json schema
+    #[arg(long, default_value_t = false)]
+    output_schema: bool,
+
     /// Write the output to a file instead of stdout or explicitly use `-` for stdout
     #[arg()]
     output_path: Option<String>,
@@ -59,7 +63,14 @@ fn main() -> Result<(), Box<dyn Error>> {
         .filter_level(opts.verbose.log_level_filter())
         .init();
 
-    main_with_args(opts)
+    // If schema is requested, print the schema and return
+    if opts.output_schema {
+        let schema = schemars::schema_for!(nixtract::DerivationDescription);
+        println!("{}", serde_json::to_string_pretty(&schema)?);
+        Ok(())
+    } else {
+        main_with_args(opts)
+    }
 }
 
 fn main_with_args(opts: Args) -> Result<(), Box<dyn Error>> {

src/nix/describe_derivation.rs

@@ -1,11 +1,12 @@
 use std::{collections::HashMap, process::Command};
 
+use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 
 use super::lib::Lib;
 use crate::error::{Error, Result};
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct DerivationDescription {
     pub attribute_path: String,
@@ -19,21 +20,21 @@ pub struct DerivationDescription {
     pub build_inputs: Vec<BuiltInput>,
 }
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct Output {
     pub name: String,
     pub output_path: Option<String>,
 }
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct ParsedName {
     pub name: String,
     pub version: String,
 }
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct NixpkgsMetadata {
     pub description: String,
@@ -44,23 +45,23 @@ pub struct NixpkgsMetadata {
     pub licenses: Option<Vec<License>>,
 }
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct Source {
     pub git_repo_url: String,
     // Revision or tag of the git repo
     pub rev: String,
 }
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct License {
     // Not all licenses in nixpkgs have an associated spdx id
     pub spdx_id: Option<String>,
     pub full_name: String,
 }
 
-#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone)]
+#[derive(Deserialize, Serialize, Debug, Eq, PartialEq, Clone, JsonSchema)]
 #[serde(rename_all(deserialize = "camelCase"))]
 pub struct BuiltInput {
     pub attribute_path: String,