Use compiler-info.json to find runtime and bsc

Author: nojaf

server/src/bsc-args/rewatch.ts

@@ -57,6 +57,7 @@ async function getRuntimePath(
 
 export async function getRewatchBscArgs(
   send: (msg: p.Message) => void,
+  bscBinaryLocation: string | null,
   projectsFiles: Map<string, projectFiles>,
   entry: IncrementallyCompiledFileInfo,
 ): Promise<RewatchCompilerArgs | null> {
@@ -124,12 +125,10 @@ export async function getRewatchBscArgs(
           "--compiler-args",
           entry.file.sourceFilePath,
         ];
-    const bscExe = await utils.findBscExeBinary(
-      entry.project.workspaceRootPath,
-    );
+
     const env: NodeJS.ProcessEnv = {};
-    if (bscExe != null) {
-      env["RESCRIPT_BSC_EXE"] = bscExe;
+    if (bscBinaryLocation != null) {
+      env["RESCRIPT_BSC_EXE"] = bscBinaryLocation;
     }
 
     // For ReScript >= 12.0.0-beta.11 we need to set RESCRIPT_RUNTIME

server/src/constants.ts

@@ -33,6 +33,11 @@ export let rescriptJsonPartialPath = "rescript.json";
 export let compilerDirPartialPath = path.join("lib", "bs");
 export let compilerOcamlDirPartialPath = path.join("lib", "ocaml");
 export let compilerLogPartialPath = path.join("lib", "bs", ".compiler.log");
+export let compilerInfoPartialPath = path.join(
+  "lib",
+  "bs",
+  "compiler-info.json",
+);
 export let buildNinjaPartialPath = path.join("lib", "bs", "build.ninja");
 export let rewatchLockPartialPath = path.join("lib", "rewatch.lock");
 export let rescriptLockPartialPath = path.join("lib", "rescript.lock");

server/src/find-runtime.ts

@@ -1,5 +1,6 @@
-import { readdir, stat as statAsync } from "fs/promises";
+import { readdir, stat as statAsync, readFile } from "fs/promises";
 import { join, resolve } from "path";
+import { compilerInfoPartialPath } from "./constants";
 
 // Efficient parallel folder traversal to find node_modules directories
 async function findNodeModulesDirs(
@@ -91,7 +92,19 @@ async function findRescriptRuntimeInAlternativeLayout(
   return results;
 }
 
-async function findRuntimePath(project: string) {
+async function findRuntimePath(project: string): Promise<string[]> {
+  // Try a compiler-info.json file first
+  const compilerInfo = resolve(project, compilerInfoPartialPath);
+  try {
+    const contents = await readFile(compilerInfo, "utf8");
+    const compileInfo: { runtime_path?: string } = JSON.parse(contents);
+    if (compileInfo && compileInfo.runtime_path) {
+      return [compileInfo.runtime_path];
+    }
+  } catch {
+    // Ignore errors, fallback to node_modules search
+  }
+
   // Find all node_modules directories using efficient traversal
   const node_modules = await findNodeModulesDirs(project);
 
@@ -136,7 +149,7 @@ async function findRuntimePath(project: string) {
   return rescriptRuntimeDirs.map((runtime) => resolve(runtime));
 }
 
-function findRuntimeCached() {
+function findRuntimeCached(): (project: string) => Promise<string[]> {
   const cache = new Map<string, string[]>();
   return async (project: string) => {
     if (cache.has(project)) {

server/src/incrementalCompilation.ts

@@ -185,7 +185,12 @@ export async function getBscArgs(
 ): Promise<BsbCompilerArgs | RewatchCompilerArgs | null> {
   return entry.buildSystem === "bsb"
     ? await getBsbBscArgs(entry)
-    : await getRewatchBscArgs(send, projectsFiles, entry);
+    : await getRewatchBscArgs(
+        send,
+        entry.project.bscBinaryLocation,
+        projectsFiles,
+        entry,
+      );
 }
 
 function argCouples(argList: string[]): string[][] {

server/src/utils.ts

@@ -92,6 +92,20 @@ let findBinary = async (
     return path.join(config.extensionConfiguration.platformPath, binary);
   }
 
+  if (projectRootPath !== null && binary === "bsc.exe") {
+    try {
+      const compilerInfo = path.resolve(
+        projectRootPath,
+        c.compilerInfoPartialPath,
+      );
+      const contents = await fsAsync.readFile(compilerInfo, "utf8");
+      const compileInfo = JSON.parse(contents);
+      if (compileInfo && compileInfo.runtime_path) {
+        return compileInfo.runtime_path;
+      }
+    } catch {}
+  }
+
   const rescriptDir = lookup.findFilePathFromProjectRoot(
     projectRootPath,
     path.join("node_modules", "rescript"),