WIP children tags rework

Goals:
- switch logic around: prepare nodes before printing docs, try to avoid modifying printed result
- respect user's wish to have line breaks sveltejs#143 sveltejs#117
- generally try to be more in line with how prettier formats things

TODO:
- either get tag break logic on par with prettier (breaking > into new lines etc) or adjust tests
- more readable tag breaking logic for multiple children tags
- tidy up

src/print/doc-helpers.ts

@@ -1,42 +1,43 @@
 import { Doc, doc } from 'prettier';
+import { findLastIndex } from './helpers';
 
-export function isLine(doc: Doc) {    
-  return typeof doc === 'object' && doc.type === 'line' 
-} 
+export function isLine(doc: Doc) {
+    return typeof doc === 'object' && doc.type === 'line';
+}
 
 export function isLineDiscardedIfLonely(doc: Doc) {
-  return isLine(doc) && !(doc as doc.builders.Line).keepIfLonely
+    return isLine(doc) && !(doc as doc.builders.Line).keepIfLonely;
 }
 
 /**
  * Check if the doc is empty, i.e. consists of nothing more than empty strings (possibly nested).
  */
 export function isEmptyDoc(doc: Doc): boolean {
-  if (typeof doc === 'string') {
-      return doc.length === 0;
-  }
+    if (typeof doc === 'string') {
+        return doc.length === 0;
+    }
 
-  if (doc.type === 'line') {
-      return !doc.keepIfLonely;
-  }
+    if (doc.type === 'line') {
+        return !doc.keepIfLonely;
+    }
 
-  const { contents } = doc as { contents?: Doc };
+    const { contents } = doc as { contents?: Doc };
 
-  if (contents) {
-      return isEmptyDoc(contents);
-  }
+    if (contents) {
+        return isEmptyDoc(contents);
+    }
 
-  const { parts } = doc as { parts?: Doc[] };
+    const { parts } = doc as { parts?: Doc[] };
 
-  if (parts) {
-      return isEmptyGroup(parts);
-  }
+    if (parts) {
+        return isEmptyGroup(parts);
+    }
 
-  return false;
+    return false;
 }
 
 export function isEmptyGroup(group: Doc[]): boolean {
-  return !group.find(doc => !isEmptyDoc(doc))
+    return !group.find((doc) => !isEmptyDoc(doc));
 }
 
 /**
@@ -95,13 +96,3 @@ function getParts(doc: Doc): Doc[] | undefined {
         return doc.parts;
     }
 }
-
-function findLastIndex<T>(isMatch: (item: T) => boolean, items: T[]) {
-    for (let i = items.length - 1; i >= 0; i--) {
-        if (isMatch(items[i])) {
-            return i;
-        }
-    }
-
-    return -1;
-}

src/print/helpers.ts

@@ -23,3 +23,13 @@ export function isPreTagContent(path: FastPath): boolean {
 export function flatten<T>(arrays: T[][]): T[] {
     return ([] as T[]).concat.apply([], arrays);
 }
+
+export function findLastIndex<T>(isMatch: (item: T) => boolean, items: T[]) {
+    for (let i = items.length - 1; i >= 0; i--) {
+        if (isMatch(items[i])) {
+            return i;
+        }
+    }
+
+    return -1;
+}