Keep track of compiler info during build

rewatch/src/build.rs

@@ -1,6 +1,7 @@
 pub mod build_types;
 pub mod clean;
 pub mod compile;
+pub mod compiler_info;
 pub mod deps;
 pub mod logs;
 pub mod namespaces;
@@ -10,6 +11,7 @@ pub mod read_compile_state;
 
 use self::parse::parser_args;
 use crate::build::compile::{mark_modules_with_deleted_deps_dirty, mark_modules_with_expired_deps_dirty};
+use crate::build::compiler_info::{CompilerCheckResult, verify_compiler_info, write_compiler_info};
 use crate::helpers::emojis::*;
 use crate::helpers::{self};
 use crate::project_context::ProjectContext;
@@ -109,6 +111,20 @@ pub fn get_compiler_args(rescript_file_path: &Path) -> Result<String> {
     Ok(result)
 }
 
+pub fn get_compiler_info(project_context: &ProjectContext) -> Result<CompilerInfo> {
+    let bsc_path = helpers::get_bsc();
+    let bsc_hash = helpers::compute_file_hash(&bsc_path).ok_or(anyhow!(
+        "Failed to compute bsc hash for {}",
+        bsc_path.to_string_lossy()
+    ))?;
+    let runtime_path = compile::get_runtime_path(&project_context.current_config, project_context)?;
+    Ok(CompilerInfo {
+        bsc_path,
+        bsc_hash,
+        runtime_path,
+    })
+}
+
 pub fn initialize_build(
     default_timing: Option<Duration>,
     filter: &Option<regex::Regex>,
@@ -117,8 +133,8 @@ pub fn initialize_build(
     build_dev_deps: bool,
     snapshot_output: bool,
 ) -> Result<BuildState> {
-    let bsc_path = helpers::get_bsc();
     let project_context = ProjectContext::new(path)?;
+    let compiler = get_compiler_info(&project_context)?;
 
     if !snapshot_output && show_progress {
         print!("{} {}Building package tree...", style("[1/7]").bold().dim(), TREE);
@@ -129,6 +145,8 @@ pub fn initialize_build(
     let packages = packages::make(filter, &project_context, show_progress, build_dev_deps)?;
     let timing_package_tree_elapsed = timing_package_tree.elapsed();
 
+    let compiler_check = verify_compiler_info(&packages, &compiler);
+
     if !snapshot_output && show_progress {
         println!(
             "{}{} {}Built package tree in {:.2}s",
@@ -139,6 +157,14 @@ pub fn initialize_build(
                 .unwrap_or(timing_package_tree_elapsed)
                 .as_secs_f64()
         );
+        if let CompilerCheckResult::CleanedPackagesDueToCompiler = compiler_check {
+            println!(
+                "{}{} {}Cleaned previous build due to compiler update",
+                LINE_CLEAR,
+                style("[1/7]").bold().dim(),
+                SWEEP
+            );
+        }
     }
 
     if !packages::validate_packages_dependencies(&packages) {
@@ -156,7 +182,7 @@ pub fn initialize_build(
         let _ = stdout().flush();
     }
 
-    let mut build_state = BuildState::new(project_context, packages, bsc_path);
+    let mut build_state = BuildState::new(project_context, packages, compiler);
     packages::parse_packages(&mut build_state);
     let timing_source_files_elapsed = timing_source_files.elapsed();
 
@@ -448,6 +474,9 @@ pub fn incremental_build(
             log_deprecations(build_state);
         }
 
+        // Write per-package compiler metadata to `lib/bs/compiler-info.json` (idempotent)
+        write_compiler_info(build_state);
+
         Ok(())
     }
 }

rewatch/src/build/build_types.rs

@@ -2,6 +2,7 @@ use crate::build::packages::{Namespace, Package};
 use crate::config::Config;
 use crate::project_context::ProjectContext;
 use ahash::{AHashMap, AHashSet};
+use blake3::Hash;
 use std::{fmt::Display, path::PathBuf, time::SystemTime};
 
 #[derive(Debug, Clone, PartialEq)]
@@ -96,10 +97,17 @@ pub struct BuildState {
     pub packages: AHashMap<String, Package>,
     pub module_names: AHashSet<String>,
     pub deleted_modules: AHashSet<String>,
-    pub bsc_path: PathBuf,
+    pub compiler_info: CompilerInfo,
     pub deps_initialized: bool,
 }
 
+#[derive(Debug, Clone)]
+pub struct CompilerInfo {
+    pub bsc_path: PathBuf,
+    pub bsc_hash: Hash,
+    pub runtime_path: PathBuf,
+}
+
 impl BuildState {
     pub fn get_package(&self, package_name: &str) -> Option<&Package> {
         self.packages.get(package_name)
@@ -111,15 +119,15 @@ impl BuildState {
     pub fn new(
         project_context: ProjectContext,
         packages: AHashMap<String, Package>,
-        bsc_path: PathBuf,
+        compiler: CompilerInfo,
     ) -> Self {
         Self {
             project_context,
             module_names: AHashSet::new(),
             modules: AHashMap::new(),
             packages,
             deleted_modules: AHashSet::new(),
-            bsc_path,
+            compiler_info: compiler,
             deps_initialized: false,
         }
     }

rewatch/src/build/clean.rs

@@ -1,5 +1,6 @@
 use super::build_types::*;
 use super::packages;
+use crate::build;
 use crate::build::packages::Package;
 use crate::config::Config;
 use crate::helpers;
@@ -332,9 +333,8 @@ pub fn cleanup_after_build(build_state: &BuildState) {
 
 pub fn clean(path: &Path, show_progress: bool, snapshot_output: bool, clean_dev_deps: bool) -> Result<()> {
     let project_context = ProjectContext::new(path)?;
-
+    let compiler_info = build::get_compiler_info(&project_context)?;
     let packages = packages::make(&None, &project_context, show_progress, clean_dev_deps)?;
-    let bsc_path = helpers::get_bsc();
 
     let timing_clean_compiler_assets = Instant::now();
     if !snapshot_output && show_progress {
@@ -364,7 +364,7 @@ pub fn clean(path: &Path, show_progress: bool, snapshot_output: bool, clean_dev_
     }
 
     let timing_clean_mjs = Instant::now();
-    let mut build_state = BuildState::new(project_context, packages, bsc_path);
+    let mut build_state = BuildState::new(project_context, packages, compiler_info);
     packages::parse_packages(&mut build_state);
     let root_config = build_state.get_root_config();
     let suffix_for_print = if snapshot_output || !show_progress {
@@ -418,7 +418,7 @@ pub fn clean(path: &Path, show_progress: bool, snapshot_output: bool, clean_dev_
     Ok(())
 }
 
-fn clean_package(show_progress: bool, snapshot_output: bool, package: &Package) {
+pub fn clean_package(show_progress: bool, snapshot_output: bool, package: &Package) {
     if show_progress {
         if snapshot_output {
             println!("Cleaning {}", package.name)
@@ -441,4 +441,7 @@ fn clean_package(show_progress: bool, snapshot_output: bool, package: &Package)
     let path_str = package.get_ocaml_build_path();
     let path = std::path::Path::new(&path_str);
     let _ = std::fs::remove_dir_all(path);
+
+    // remove the per-package compiler metadata file so that a subsequent build writes fresh metadata
+    let _ = std::fs::remove_file(package.get_compiler_info_path());
 }

rewatch/src/build/compile.rs

@@ -16,7 +16,9 @@ use console::style;
 use log::{debug, trace};
 use rayon::prelude::*;
 use std::path::Path;
+use std::path::PathBuf;
 use std::process::Command;
+use std::sync::OnceLock;
 use std::time::SystemTime;
 
 pub fn compile(
@@ -336,22 +338,36 @@ pub fn compile(
     Ok((compile_errors, compile_warnings, num_compiled_modules))
 }
 
-pub fn get_runtime_path_args(
-    package_config: &Config,
-    project_context: &ProjectContext,
-) -> Result<Vec<String>> {
-    match std::env::var("RESCRIPT_RUNTIME") {
-        Ok(runtime_path) => Ok(vec!["-runtime-path".to_string(), runtime_path]),
+static RUNTIME_PATH_MEMO: OnceLock<PathBuf> = OnceLock::new();
+
+pub fn get_runtime_path(package_config: &Config, project_context: &ProjectContext) -> Result<PathBuf> {
+    if let Some(p) = RUNTIME_PATH_MEMO.get() {
+        return Ok(p.clone());
+    }
+
+    let resolved = match std::env::var("RESCRIPT_RUNTIME") {
+        Ok(runtime_path) => Ok(PathBuf::from(runtime_path)),
         Err(_) => match helpers::try_package_path(package_config, project_context, "@rescript/runtime") {
-            Ok(runtime_path) => Ok(vec![
-                "-runtime-path".to_string(),
-                runtime_path.to_string_lossy().to_string(),
-            ]),
+            Ok(runtime_path) => Ok(runtime_path),
             Err(err) => Err(anyhow!(
                 "The rescript runtime package could not be found.\nPlease set RESCRIPT_RUNTIME environment variable or make sure the runtime package is installed.\nError: {err}"
             )),
         },
-    }
+    }?;
+
+    let _ = RUNTIME_PATH_MEMO.set(resolved.clone());
+    Ok(resolved)
+}
+
+pub fn get_runtime_path_args(
+    package_config: &Config,
+    project_context: &ProjectContext,
+) -> Result<Vec<String>> {
+    let runtime_path = get_runtime_path(package_config, project_context)?;
+    Ok(vec![
+        "-runtime-path".to_string(),
+        runtime_path.to_string_lossy().to_string(),
+    ])
 }
 
 pub fn compiler_args(
@@ -581,7 +597,7 @@ fn compile_file(
     let BuildState {
         packages,
         project_context,
-        bsc_path,
+        compiler_info,
         ..
     } = build_state;
     let root_config = build_state.get_root_config();
@@ -612,7 +628,7 @@ fn compile_file(
         package.is_local_dep,
     )?;
 
-    let to_mjs = Command::new(bsc_path)
+    let to_mjs = Command::new(&compiler_info.bsc_path)
         .current_dir(
             build_path_abs
                 .canonicalize()