Initial implementation of js-post-build in rewatch (#8151)

* Initial implementation of js-post-build in rewatch

* Add changelog

Author: nojaf

CHANGELOG.md

@@ -22,6 +22,7 @@
 - Reanalyze: add reactive incremental analysis (`-reactive`, `-runs`, `-churn`) and Mermaid pipeline dumping (`-mermaid`). https://github.com/rescript-lang/rescript/pull/8092
 
 - Reanalyze: add `reanalyze-server` (long-lived server) with transparent delegation for `rescript-tools reanalyze -json`. https://github.com/rescript-lang/rescript/pull/8127
+- Add support of `js-post-build` in Rewatch. Note that `${file}` is now an absolute path. https://github.com/rescript-lang/rescript/pull/8151
 
 #### :bug: Bug fix
 

rewatch/CompilerConfigurationSpec.md

@@ -22,7 +22,7 @@ This document contains a list of all bsconfig parameters with remarks, and wheth
 | warnings              | Warnings                |        |     [x]      |
 | ppx-flags             | array of string         |        |     [x]      |
 | pp-flags              | array of string         |        |     [_]      |
-| js-post-build         | Js-Post-Build           |        |     [_]      |
+| js-post-build         | Js-Post-Build           |    `${file}` is now an absolute path    |     [x]      |
 | package-specs         | array of Module-Format  |        |     [_]      |
 | package-specs         | array of Package-Spec   |        |     [x]      |
 | entries               | array of Target-Item    |        |     [_]      |
@@ -135,7 +135,7 @@ Currently supported features:
 
 | Parameter | JSON type | Remark | Implemented? |
 | --------- | --------- | ------ | :----------: |
-| cmd       | string    |        |     [_]      |
+| cmd       | string    |    `${file}` is now an absolute path    |     [x]      |
 
 ### Package-Spec
 

rewatch/src/build/compile.rs

@@ -21,6 +21,33 @@ use std::process::Command;
 use std::sync::OnceLock;
 use std::time::SystemTime;
 
+/// Execute js-post-build command for a compiled JavaScript file.
+/// Unlike bsb which passes relative paths, rewatch passes absolute paths for clarity.
+fn execute_post_build_command(cmd: &str, js_file_path: &Path) -> Result<()> {
+    let full_command = format!("{} {}", cmd, js_file_path.display());
+
+    let output = if cfg!(target_os = "windows") {
+        Command::new("cmd").args(["/C", &full_command]).output()
+    } else {
+        Command::new("sh").args(["-c", &full_command]).output()
+    };
+
+    match output {
+        Ok(output) if !output.status.success() => {
+            let stderr = String::from_utf8_lossy(&output.stderr);
+            let stdout = String::from_utf8_lossy(&output.stdout);
+            Err(anyhow!(
+                "js-post-build command failed for {}: {}{}",
+                js_file_path.display(),
+                stderr,
+                stdout
+            ))
+        }
+        Err(e) => Err(anyhow!("Failed to execute js-post-build command: {}", e)),
+        Ok(_) => Ok(()),
+    }
+}
+
 pub fn compile(
     build_state: &mut BuildCommandState,
     show_progress: bool,
@@ -815,6 +842,29 @@ fn compile_file(
                 }
             });
 
+            // Execute js-post-build command if configured
+            // Only run for implementation files (not interfaces)
+            if !is_interface
+                && let Some(js_post_build) = &package.config.js_post_build
+                && let SourceType::SourceFile(SourceFile {
+                    implementation: Implementation { path, .. },
+                    ..
+                }) = &module.source_type
+            {
+                // Execute post-build command for each package spec (each output format)
+                for spec in root_config.get_package_specs() {
+                    let js_file = helpers::get_source_file_from_rescript_file(
+                        &package.get_build_path().join(path),
+                        &root_config.get_suffix(&spec),
+                    );
+
+                    if js_file.exists() {
+                        // Fail the build if post-build command fails (matches bsb behavior with &&)
+                        execute_post_build_command(&js_post_build.cmd, &js_file)?;
+                    }
+                }
+            }
+
             if helpers::contains_ascii_characters(&err) {
                 if package.is_local_dep {
                     // suppress warnings of external deps

rewatch/src/config.rs

@@ -219,6 +219,13 @@ pub struct JsxSpecs {
 /// We do not care about the internal structure because the gentype config is loaded by bsc.
 pub type GenTypeConfig = serde_json::Value;
 
+/// Configuration for running a command after each JavaScript file is compiled.
+/// Note: Unlike bsb, rewatch passes absolute paths to the command for clarity.
+#[derive(Deserialize, Debug, Clone)]
+pub struct JsPostBuild {
+    pub cmd: String,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, PartialOrd)]
 pub enum DeprecationWarning {
     BsDependencies,
@@ -299,6 +306,8 @@ pub struct Config {
     pub experimental_features: Option<HashMap<ExperimentalFeature, bool>>,
     #[serde(rename = "gentypeconfig")]
     pub gentype_config: Option<GenTypeConfig>,
+    #[serde(rename = "js-post-build")]
+    pub js_post_build: Option<JsPostBuild>,
     // Used by the VS Code extension; ignored by rewatch but should not emit warnings.
     // Payload is not validated here, only in the VS Code extension.
     pub editor: Option<serde_json::Value>,
@@ -707,7 +716,6 @@ impl Config {
             "generators",
             "cut-generators",
             "pp-flags",
-            "js-post-build",
             "entries",
             "use-stdlib",
             "external-stdlib",
@@ -800,6 +808,7 @@ pub mod tests {
             namespace: None,
             jsx: None,
             gentype_config: None,
+            js_post_build: None,
             editor: None,
             namespace_entry: None,
             deprecation_warnings: vec![],

tests/build_tests/post-build/input.js

@@ -3,14 +3,14 @@
 import * as assert from "node:assert";
 import { setup } from "#dev/process";
 
-const { execBuildLegacy } = setup(import.meta.dirname);
+const { execBuild } = setup(import.meta.dirname);
 
 if (process.platform === "win32") {
   console.log("Skipping test on Windows");
   process.exit(0);
 }
 
-const out = await execBuildLegacy();
+const out = await execBuild();
 
 if (out.status !== 0) {
   assert.fail(out.stdout + out.stderr);