Use the path provided by serverless as the base

src/index.ts

@@ -1,5 +1,5 @@
 import * as path from 'path'
-import { statSync, realpathSync } from 'fs'
+import { statSync } from 'fs'
 import set from 'lodash.set'
 import difference from 'lodash.difference'
 import merge from './merge'
@@ -9,7 +9,6 @@ const SERVERLESS = 'serverless'
 const DIRNAME = 'dirname'
 const JS_EXTNAME = '.js'
 const CONFIG_EXTNAMES = new Set(['.yml', '.yaml', JS_EXTNAME])
-const REALPATH = realpathSync('.')
 
 interface ImportedConfig {
   custom?: {
@@ -39,7 +38,7 @@ class ImportConfigPlugin {
     this.serverless = serverless
     this.originalPlugins = this.serverless.service.plugins?.slice() ?? []
 
-    this.importConfigs(this.serverless.service, { basedir: REALPATH })
+    this.importConfigs(this.serverless.service, { basedir: this.serverless.serviceDir })
     this.loadImportedPlugins()
   }
 
@@ -99,12 +98,12 @@ class ImportConfigPlugin {
   }
 
   private prepareImportedConfig(options: { importPath: string, config: ImportedConfig }) {
-    const { variables } = this.serverless
+    const { variables, serviceDir } = this.serverless
     const { importPath, config } = options
 
     // make all function handlers relative to the imported config file
     const { functions } = config
-    const importDir = path.relative(REALPATH, path.dirname(importPath))
+    const importDir = path.relative(serviceDir, path.dirname(importPath))
     const toPosixPath = (location: string) => location.split(path.sep).join(path.posix.sep);
     if (functions != null) {
       Object.values(functions).forEach(func => {

src/serverless.d.ts

@@ -23,6 +23,8 @@ declare namespace Serverless {
       }
     }
 
+    serviceDir: string
+
     utils: {
       readFileSync: (path: string) => object
     }