add basic support for importing from neighbouring packages

javascript/ql/src/semmle/javascript/Modules.qll

@@ -174,7 +174,8 @@ abstract class Import extends ASTNode {
       result = resolveAsProvidedModule() or
       result = resolveImportedPath() or
       result = resolveFromTypeRoot() or
-      result = resolveFromTypeScriptSymbol()
+      result = resolveFromTypeScriptSymbol() or
+      result = resolveNeighbourPackage(this.getImportedPath().getValue())
     )
   }
 
@@ -196,3 +197,28 @@ abstract deprecated class PathExprInModule extends PathExpr {
     this.(Comment).getTopLevel() instanceof Module
   }
 }
+
+/**
+ * Gets a module imported from another package in the same repository.
+ *
+ * No support for importing from folders inside the other package.
+ */
+private Module resolveNeighbourPackage(PathString importPath) {
+  exists(PackageJSON json | importPath = json.getPackageName() and result = json.getMainModule())
+  or
+  exists(string package |
+    result.getFile().getParentContainer() = getPackageFolder(package) and
+    importPath = package + "/" + [result.getFile().getBaseName(), result.getFile().getStem()]
+  )
+}
+
+/**
+ * Gets the folder for a package that has name `package` according to a package.json file in the resulting folder.
+ */
+pragma[noinline]
+private Folder getPackageFolder(string package) {
+  exists(PackageJSON json |
+    json.getPackageName() = package and
+    result = json.getFile().getParentContainer()
+  )
+}