Introduce immutable query fragments

src/queryBuilder.ts

@@ -2,29 +2,37 @@ export abstract class QueryBuilder {
   __query: string = ""
 
   public constructor() {
-    this.__attr("__typename")
+    this.__attr("__typename", true)
     if (typeof (this as any).id === "function") (this as any).id()
   }
 
-  protected __attr(attr: string): this {
-    return this._(attr)
+  protected __attr(attr: string, mutable?: boolean): this {
+    return this._(attr, mutable)
+  }
+
+  public __clone() {
+    return Object.assign(Object.create(Object.getPrototypeOf(this)), this)
   }
 
   // raw is exposed, to be able to add free form gql in the middle
-  public _(str: string): this {
-    this.__query += `${str}\n` // TODO: restore depth / formatting by passing base depth to constructor: ${"".padStart(this.__qb.stack.length * 2)}
-    return this
+  public _(str: string, mutable?: boolean): this {
+    if (mutable || str === "id") {
+      this.__query += `${str}\n`
+      return this
+    } else {
+      const clone = this.__clone()
+      clone.__query += `${str}\n`
+
+      return clone
+    }
   }
 
   protected __child<T extends QueryBuilder>(
     childName: string,
     childType: new () => T,
     builder?: string | ((q: T) => T) | T
   ): this {
-    this._(`${childName} {\n`)
-    this.__buildChild(childType, builder)
-    this._(`}`)
-    return this
+    return this._(`${childName} {\n`).__buildChild(childType, builder)._(`}`)
   }
 
   // used for interfaces and unions
@@ -45,13 +53,16 @@ export abstract class QueryBuilder {
   ) {
     // already instantiated child builder
     if (builder instanceof QueryBuilder) {
-      this._(builder.toString())
+      return this._(builder.toString())
     } else {
-      const childBuilder = new childType()
-      if (typeof builder === "string") childBuilder._(builder)
-      else if (typeof builder === "function") builder(childBuilder)
-      // undefined is ok as well, no fields at all
-      this._(childBuilder.toString())
+      const baseChildBuilder = new childType()
+      const childBuilder =
+        typeof builder === "string"
+          ? baseChildBuilder._(builder)
+          : typeof builder === "function"
+          ? builder(baseChildBuilder)
+          : baseChildBuilder
+      return this._(childBuilder.toString())
     }
   }