Change config context when referencing outside the main project

src/config-loader.ts

@@ -1,4 +1,5 @@
 import * as TsConfigLoader2 from "./tsconfig-loader";
+import { MatchPath, createMatchPath } from "./match-path-sync";
 import * as path from "path";
 
 export interface ExplicitParams {
@@ -87,3 +88,35 @@ export function configLoader({
     addMatchAll: loadResult.baseUrl !== undefined,
   };
 }
+
+export function findConfigMatcher({
+  cwd,
+  explicitParams,
+}: ConfigLoaderParams):
+  | { config: ConfigLoaderSuccessResult; matchPath: MatchPath }
+  | undefined {
+  const configLoaderResult = configLoader({
+    cwd,
+    explicitParams,
+  });
+
+  if (configLoaderResult.resultType === "failed") {
+    console.warn(
+      "".concat(configLoaderResult.message, ". tsconfig-paths will be skipped")
+    );
+
+    return;
+  }
+
+  const matchPath = createMatchPath(
+    configLoaderResult.absoluteBaseUrl,
+    configLoaderResult.paths,
+    configLoaderResult.mainFields,
+    configLoaderResult.addMatchAll
+  );
+
+  return {
+    config: configLoaderResult,
+    matchPath,
+  };
+}

src/register.ts

@@ -1,11 +1,14 @@
-import { createMatchPath } from "./match-path-sync";
-import { configLoader, ExplicitParams } from "./config-loader";
+import * as path from "path";
+
+import { findConfigMatcher, ExplicitParams } from "./config-loader";
 
 const noOp = (): void => void 0;
 
 function getCoreModules(
   builtinModules: string[] | undefined
-): { [key: string]: boolean } {
+): {
+  [key: string]: boolean;
+} {
   builtinModules = builtinModules || [
     "assert",
     "buffer",
@@ -76,25 +79,16 @@ export function register(params?: RegisterParams): () => void {
     cwd = argv.project;
   }
 
-  const configLoaderResult = configLoader({
-    cwd: cwd ?? process.cwd(),
+  const primaryMatcher = findConfigMatcher({
+    cwd: cwd !== null && cwd !== void 0 ? cwd : process.cwd(),
     explicitParams,
   });
 
-  if (configLoaderResult.resultType === "failed") {
-    console.warn(
-      `${configLoaderResult.message}. tsconfig-paths will be skipped`
-    );
-
+  if (!primaryMatcher) {
     return noOp;
   }
 
-  const matchPath = createMatchPath(
-    configLoaderResult.absoluteBaseUrl,
-    configLoaderResult.paths,
-    configLoaderResult.mainFields,
-    configLoaderResult.addMatchAll
-  );
+  const configMatchers = [primaryMatcher];
 
   // Patch node's module loading
   // eslint-disable-next-line @typescript-eslint/no-require-imports,@typescript-eslint/no-var-requires
@@ -103,10 +97,30 @@ export function register(params?: RegisterParams): () => void {
   const originalResolveFilename = Module._resolveFilename;
   const coreModules = getCoreModules(Module.builtinModules);
   // eslint-disable-next-line @typescript-eslint/no-explicit-any,no-underscore-dangle
-  Module._resolveFilename = function (request: string, _parent: any): string {
+  Module._resolveFilename = function (request: string, parent: any): string {
     const isCoreModule = coreModules.hasOwnProperty(request);
     if (!isCoreModule) {
-      const found = matchPath(request);
+      const parentFilename = parent?.filename;
+
+      let matcher = configMatchers.find(
+        ({ config }) =>
+          !parentFilename || parentFilename.startsWith(config.absoluteBaseUrl)
+      );
+
+      if (!matcher) {
+        const targetProject = path.dirname(parentFilename);
+
+        matcher = findConfigMatcher({
+          cwd: targetProject,
+          explicitParams,
+        });
+
+        if (matcher) {
+          configMatchers.push(matcher);
+        }
+      }
+
+      const found = matcher?.matchPath(request);
       if (found) {
         const modifiedArguments = [found, ...[].slice.call(arguments, 1)]; // Passes all arguments. Even those that is not specified above.
         return originalResolveFilename.apply(this, modifiedArguments);