Handle comments when indenting method chains

Previously, indentation went wrong when the comment on the line above
looked like a method call/member access:

    fn main() {
        // Lorem ipsum lorem ipsum lorem ipsum lorem.ipsum
                                                foo.bar()
    }

With this patch:

    fn main() {
        // Lorem ipsum lorem ipsum lorem ipsum lorem.ipsum
        foo.bar()
    }

Also, a blank line or a comment broke method-chain indentation:

    fn main() {
        something.a.do_it
        // A comment
            .aligned

            .more_alignment();
    }

With this patch:

    fn main() {
        something.a.do_it
        // A comment
                   .aligned

                   .more_alignment();
    }

Note that comments interleaving a method chain are not aligned with the
'.' of the method chain.

Author: mrBliss

rust-mode-tests.el

@@ -1599,6 +1599,19 @@ fn main() {
 "
    )))
 
+(ert-deftest indent-method-chains-look-over-comment ()
+  (let ((rust-indent-method-chain t)) (test-indent
+   "
+fn main() {
+    thing.a.do_it
+    // A comment
+           .aligned
+    // Another comment
+           .more_alignment();
+}
+"
+   )))
+
 (ert-deftest indent-method-chains-comment ()
   (let ((rust-indent-method-chain t)) (test-indent
    "
@@ -1627,6 +1640,17 @@ fn main() { // comment here should not push next line out
 "
    )))
 
+(ert-deftest indent-method-chains-after-comment2 ()
+  (let ((rust-indent-method-chain t)) (test-indent
+   "
+fn main() {
+    // Lorem ipsum lorem ipsum lorem ipsum lorem.ipsum
+    foo.bar()
+}
+"
+   )))
+
+
 (ert-deftest test-for-issue-36-syntax-corrupted-state ()
   "This is a test for a issue #36, which involved emacs's
 internal state getting corrupted when actions were done in a

rust-mode.el

@@ -301,6 +301,17 @@ buffer."
     (when (looking-at (concat "\s*\." rust-re-ident))
       (forward-line -1)
       (end-of-line)
+      ;; Keep going up (looking for a line that could contain a method chain)
+      ;; while we're in a comment or on a blank line. Stop when the paren
+      ;; level changes.
+      (let ((level (rust-paren-level)))
+        (while (and (or (rust-in-str-or-cmnt)
+                        ;; Only whitespace (or nothing) from the beginning to
+                        ;; the end of the line.
+                        (looking-back "^\s*" (point-at-bol)))
+                    (= (rust-paren-level) level))
+          (forward-line -1)
+          (end-of-line)))
 
       (let
           ;; skip-dot-identifier is used to position the point at the