Allow rendering a BUILD file for a single crate

crate_universe/src/cli.rs

@@ -2,6 +2,7 @@
 
 mod generate;
 mod query;
+mod render;
 mod splice;
 mod vendor;
 
@@ -15,12 +16,14 @@ use tracing_subscriber::FmtSubscriber;
 
 pub use self::generate::GenerateOptions;
 pub use self::query::QueryOptions;
+pub use self::render::RenderOptions;
 pub use self::splice::SpliceOptions;
 pub use self::vendor::VendorOptions;
 
 // Entrypoints
 pub use generate::generate;
 pub use query::query;
+pub use render::render;
 pub use splice::splice;
 pub use vendor::vendor;
 
@@ -42,6 +45,9 @@ pub enum Options {
 
     /// Vendor BUILD files to the workspace with either repository definitions or `cargo vendor` generated sources.
     Vendor(VendorOptions),
+
+    /// Render a BUILD file for a single crate.
+    Render(RenderOptions),
 }
 
 // Convenience wrappers to avoid dependencies in the binary
@@ -51,7 +57,7 @@ pub fn parse_args() -> Options {
     Options::parse()
 }
 
-const EXPECTED_LOGGER_NAMES: [&str; 4] = ["Generate", "Splice", "Query", "Vendor"];
+const EXPECTED_LOGGER_NAMES: [&str; 5] = ["Generate", "Splice", "Query", "Vendor", "Render"];
 
 /// A wrapper for the tracing-subscriber default [FormatEvent]
 /// that prepends the name of the active CLI option.

crate_universe/src/cli/render.rs

@@ -0,0 +1,57 @@
+use crate::config::RenderConfig;
+use crate::context::CrateContext;
+use crate::rendering::{Platforms, Renderer};
+use crate::utils::target_triple::TargetTriple;
+
+use anyhow::{Context, Result};
+use clap::Parser;
+use serde::{Deserialize, Serialize};
+
+use std::collections::BTreeSet;
+use std::path::PathBuf;
+
+#[derive(Parser, Debug)]
+#[clap(about = "Command line options for the `render` subcommand", version)]
+pub struct RenderOptions {
+    #[clap(long)]
+    options_json: String,
+
+    #[clap(long)]
+    output_path: PathBuf,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct StructuredRenderOptions {
+    config: RenderConfig,
+
+    supported_platform_triples: BTreeSet<TargetTriple>,
+
+    platforms: Platforms,
+
+    crate_context: CrateContext,
+}
+
+pub fn render(opt: RenderOptions) -> Result<()> {
+    let RenderOptions {
+        options_json,
+        output_path,
+    } = opt;
+
+    let deserialized_options = serde_json::from_str(&options_json)
+        .with_context(|| format!("Failed to deserialize options_json from '{}'", options_json))?;
+
+    let StructuredRenderOptions {
+        config,
+        supported_platform_triples,
+        platforms,
+        crate_context,
+    } = deserialized_options;
+
+    let renderer = Renderer::new(config, supported_platform_triples);
+    let output = renderer.render_one_build_file(&platforms, &crate_context)
+        .with_context(|| format!("Failed to render BUILD.bazel file for crate {}", crate_context.name))?;
+    std::fs::write(&output_path, output.as_bytes())
+        .with_context(|| format!("Failed to write BUILD.bazel file to {}", output_path.display()))?;
+
+    Ok(())
+}

crate_universe/src/main.rs

@@ -25,5 +25,9 @@ fn main() -> cli::Result<()> {
             cli::init_logging("Vendor", verbose_logging);
             cli::vendor(opt)
         }
+        cli::Options::Render(opt) => {
+            cli::init_logging("Render", verbose_logging);
+            cli::render(opt)
+        }
     }
 }

crate_universe/src/rendering.rs

@@ -296,7 +296,7 @@ impl Renderer {
             .collect()
     }
 
-    fn render_one_build_file(&self, platforms: &Platforms, krate: &CrateContext) -> Result<String> {
+    pub(crate) fn render_one_build_file(&self, platforms: &Platforms, krate: &CrateContext) -> Result<String> {
         let mut starlark = Vec::new();
 
         // Banner comment for top of the file.