Add JSON schema generation as a hidden CLI command

Cargo.toml

@@ -132,6 +132,7 @@ wild = { version = "2.1.0", optional = true }
 
 # JSON schema
 schemars = { version = "0.8.16", optional = true }
+pretty_assertions = { version = "1.3.0", optional = true }
 
 [dev-dependencies]
 expect-test = "1.4.1"
@@ -161,7 +162,7 @@ upload = [
     "dep:dirs",
 ]
 
-schemars = ["dep:schemars"]
+schemars = ["dep:schemars", "dep:pretty_assertions"]
 
 # keyring doesn't support *BSD so it's not enabled in `full` by default
 password-storage = ["upload", "keyring"]

src/generate_json_schema.rs

@@ -0,0 +1,63 @@
+#![cfg(feature = "schemars")]
+use std::fs;
+use std::path::PathBuf;
+
+use anyhow::{bail, Result};
+use pretty_assertions::StrComparison;
+use schemars::schema_for;
+
+use crate::pyproject_toml::ToolMaturin;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, clap::ValueEnum, Default)]
+/// The mode to use when generating the JSON schema.
+pub enum Mode {
+    /// Write the JSON schema to the file.
+    #[default]
+    Write,
+    /// Check if the JSON schema is up-to-date.
+    Check,
+    /// Print the JSON schema to stdout.
+    DryRun,
+}
+
+/// Generate the JSON schema for the `pyproject.toml` file.
+#[derive(Debug, clap::Parser)]
+pub struct GenerateJsonSchemaOptions {
+    /// The mode to use when generating the JSON schema.
+    #[arg(long, default_value_t, value_enum)]
+    pub mode: Mode,
+}
+
+/// Generate the JSON schema for the `pyproject.toml` file.
+pub fn generate_json_schema(args: GenerateJsonSchemaOptions) -> Result<()> {
+    let schema = schema_for!(ToolMaturin);
+    let schema_string = serde_json::to_string_pretty(&schema).unwrap();
+    let filename = "maturin.schema.json";
+    let schema_path = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join(filename);
+
+    match args.mode {
+        Mode::DryRun => {
+            println!("{schema_string}");
+        }
+        Mode::Check => {
+            let current = fs::read_to_string(schema_path)?;
+            if current == schema_string {
+                println!("Up-to-date: {filename}");
+            } else {
+                let comparison = StrComparison::new(&current, &schema_string);
+                bail!("{filename} changed, please run `cargo run --features schemars -- generate-json-schema`:\n{comparison}",);
+            }
+        }
+        Mode::Write => {
+            let current = fs::read_to_string(&schema_path)?;
+            if current == schema_string {
+                println!("Up-to-date: {filename}");
+            } else {
+                println!("Updating: {filename}");
+                fs::write(schema_path, schema_string.as_bytes())?;
+            }
+        }
+    }
+
+    Ok(())
+}

src/lib.rs

@@ -28,6 +28,8 @@ pub use crate::build_options::{BuildOptions, CargoOptions};
 pub use crate::cargo_toml::CargoToml;
 pub use crate::compile::{compile, BuildArtifact};
 pub use crate::develop::{develop, DevelopOptions};
+#[cfg(feature = "schemars")]
+pub use crate::generate_json_schema::{generate_json_schema, GenerateJsonSchemaOptions, Mode};
 pub use crate::metadata::{Metadata23, WheelMetadata};
 pub use crate::module_writer::{
     write_dist_info, ModuleWriter, PathWriter, SDistWriter, WheelWriter,
@@ -51,6 +53,7 @@ pub mod ci;
 mod compile;
 mod cross_compile;
 mod develop;
+mod generate_json_schema;
 mod metadata;
 mod module_writer;
 #[cfg(feature = "scaffolding")]

src/main.rs

@@ -16,6 +16,8 @@ use maturin::{
     develop, write_dist_info, BridgeModel, BuildOptions, CargoOptions, DevelopOptions, PathWriter,
     PlatformTag, PythonInterpreter, Target,
 };
+#[cfg(feature = "schemars")]
+use maturin::{generate_json_schema, GenerateJsonSchemaOptions};
 #[cfg(feature = "upload")]
 use maturin::{upload_ui, PublishOpt};
 use std::env;
@@ -141,6 +143,10 @@ enum Opt {
     #[cfg(feature = "zig")]
     #[command(subcommand, hide = true)]
     Zig(Zig),
+    /// Generate the JSON schema for the `pyproject.toml` file.
+    #[cfg(feature = "schemars")]
+    #[command(name = "generate-json-schema", hide = true)]
+    GenerateJsonSchema(GenerateJsonSchemaOptions),
 }
 
 /// Backend for the PEP 517 integration. Not for human consumption
@@ -425,6 +431,8 @@ fn run() -> Result<()> {
                 .execute()
                 .context("Failed to run zig linker wrapper")?;
         }
+        #[cfg(feature = "schemars")]
+        Opt::GenerateJsonSchema(args) => generate_json_schema(args)?,
     }
 
     Ok(())