Add chained indentation to js-mode

Bug#20896
* lisp/progmodes/js.el (js-chain-indent): New variable.
(js--skip-term-backward, js--skip-terms-backward)
(js--chained-expression-p): New functions.
(js--proper-indentation): Call js--chained-expression-p.
* test/manual/indent/js-chain.js: New file.
* test/manual/indent/js.js: Add (non-)chained indentation test.

2 files changed, 33 insertions, 0 deletions

diff --git a/test/manual/indent/js-chain.js b/test/manual/indent/js-chain.js
new file mode 100644
index 00000000000..2a290294026
--- /dev/null
+++ b/test/manual/indent/js-chain.js
@@ -0,0 +1,29 @@
+// Normal chaining.
+let x = svg.mumble()
+           .zzz;
+
+// Chaining with an intervening line comment.
+let x = svg.mumble()		// line comment
+           .zzz;
+
+// Chaining with multiple dots.
+let x = svg.selectAll().something()
+           .zzz;
+
+// Nested chaining.
+let x = svg.selectAll(d3.svg.something()
+                        .zzz);
+
+// Nothing to chain to.
+let x = svg()
+    .zzz;
+
+// Nothing to chain to.
+let x = svg().mumble.x() + 73
+    .zzz;
+
+// Local Variables:
+// indent-tabs-mode: nil
+// js-chain-indent: t
+// js-indent-level: 2
+// End:
diff --git a/test/manual/indent/js.js b/test/manual/indent/js.js
index d004b82f8bc..846c3a1a5c2 100644
--- a/test/manual/indent/js.js
+++ b/test/manual/indent/js.js
@@ -124,6 +124,10 @@ if (x > 72 &&
   do_something();
 }
 
+// Test that chaining doesn't happen when js-chain-indent is nil.
+let x = svg.mumble()
+    .zzz;
+
 // Local Variables:
 // indent-tabs-mode: nil
 // js-indent-level: 2