[Refactor] re-implement 'isSubpath' without building a dynamic regex

src/core/importType.js

@@ -29,13 +29,15 @@ function isExternalPath(path, name, settings) {
 }
 
 function isSubpath(subpath, path) {
-  const subpathRegExpSrc = escapeRegExp(subpath.replace(/[/]$/, ''))
-  const subpathRegExp = new RegExp(`${isAbsolute(subpath) ? '^' : '(?:^|/)'}${subpathRegExpSrc}(?:/|$)`)
-  return subpathRegExp.test(path)
-}
-
-function escapeRegExp(string) {
-  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+  const normSubpath = subpath.replace(/[/]$/, '')
+  if (normSubpath.length === 0) {
+    return false
+  }
+  const left = path.indexOf(normSubpath)
+  const right = left + normSubpath.length
+  return left !== -1 &&
+        (left === 0 || normSubpath[0] !== '/' && path[left - 1] === '/') &&
+        (right >= path.length || path[right] === '/')
 }
 
 const externalModuleRegExp = /^\w/