Update source map handling to be reentrant

Rather than repeating the original location when we exit a node, we need to restore the previous parent’s original line location, since the source map format denotes the start location.

packages/babel-generator/src/printer.js

@@ -46,7 +46,7 @@ export default class Printer extends Buffer {
 
     if (opts.before) opts.before();
 
-    this.map.mark(node, "start");
+    this.map.mark(node);
 
     this._print(node, parent);
 
@@ -58,7 +58,7 @@ export default class Printer extends Buffer {
     if (needsParens) this.push(")");
 
     // end
-    this.map.mark(node, "end");
+    if (parent) this.map.mark(parent);
     if (opts.after) opts.after();
 
     this.format.concise = oldConcise;

packages/babel-generator/src/source-map.js

@@ -40,7 +40,7 @@ export default class SourceMap {
    * Mark a node's generated position, and add it to the sourcemap.
    */
 
-  mark(node, type) {
+  mark(node) {
     let loc = node.loc;
     if (!loc) return; // no location info
 
@@ -56,7 +56,7 @@ export default class SourceMap {
       column: position.column
     };
 
-    let original = loc[type];
+    let original = loc.start;
 
     // Avoid emitting duplicates on either side. Duplicated
     // original values creates unnecesssarily large source maps