Add new option to support compiling a single project

compiler/crates/relay-bin/src/main.rs

@@ -56,6 +56,10 @@ struct CompileCommand {
     #[clap(long, short)]
     watch: bool,
 
+    /// Compile a single project
+    #[clap(long, short)]
+    project: Option<String>,
+
     /// Compile using this config file. If not provided, searches for a config in
     /// package.json under the `relay` key or `relay.config.json` files among other up
     /// from the current working directory.
@@ -205,6 +209,10 @@ async fn handle_compiler_command(command: CompileCommand) -> Result<(), Error> {
 
     let mut config = get_config(command.config)?;
 
+    if let Some(project_to_retain) = command.project {
+        config.retain_project(project_to_retain);
+    }
+
     if command.validate {
         config.artifact_writer = Box::new(ArtifactValidationWriter::default());
     }

compiler/crates/relay-compiler/src/compiler_state.rs

@@ -61,6 +61,11 @@ impl ProjectSet {
         existing_names.push(project_name);
     }
 
+    pub fn retain_project(&mut self, project_name_to_keep: ProjectName) {
+        self.0
+            .retain(|project_name| *project_name == project_name_to_keep);
+    }
+
     pub fn iter(&self) -> slice::Iter<'_, StringKey> {
         self.0.iter()
     }

compiler/crates/relay-compiler/src/config.rs

@@ -39,6 +39,7 @@ use sha1::{Digest, Sha1};
 use std::env::current_dir;
 use std::ffi::OsStr;
 use std::path::{Path, PathBuf};
+use std::str::FromStr;
 use std::sync::Arc;
 use std::{fmt, vec};
 use watchman_client::pdu::ScmAwareClockData;
@@ -400,6 +401,18 @@ Example file:
             .filter(|project_config| project_config.enabled)
     }
 
+    // Remove projects other than `project_name_to_retain`. Used for the `--project` flag.
+    pub fn retain_project(&mut self, project_name_to_retain: String) {
+        let project_name_to_retain = StringKey::from_str(project_name_to_retain.as_str()).unwrap();
+
+        self.projects
+            .retain(|key, _| *key == project_name_to_retain);
+
+        for (_, project_set) in &mut self.sources {
+            project_set.retain_project(project_name_to_retain);
+        }
+    }
+
     /// Validated internal consistency of the config.
     fn validate_consistency(&self, errors: &mut Vec<ConfigValidationError>) {
         let mut project_names = FnvHashSet::default();
@@ -510,7 +523,11 @@ impl fmt::Debug for Config {
         } = self;
 
         fn option_fn_to_string<T>(option: &Option<T>) -> &'static str {
-            if option.is_some() { "Some(Fn)" } else { "None" }
+            if option.is_some() {
+                "Some(Fn)"
+            } else {
+                "None"
+            }
         }
 
         f.debug_struct("Config")