[Fix #619] Fix clojure-thread-last-all breaking forms with line comments

The dangling-parens join in clojure--thread-last would merge closing
parens onto a line ending in a comment, absorbing them into the
comment and making the form invalid. Now checks for a preceding
comment before joining.

Author: bbatsov

CHANGELOG.md

@@ -22,6 +22,7 @@
 * [#600](https://github.com/clojure-emacs/clojure-mode/issues/600): Fix `clojure--valid-put-clojure-indent-call-p` rejecting valid indent specs with nested lists (e.g. `letfn`'s `(1 ((:defn)) nil)`).
 * [#365](https://github.com/clojure-emacs/clojure-mode/issues/365): Font-lock function names in `letfn` bindings with `font-lock-function-name-face`.
 * [#527](https://github.com/clojure-emacs/clojure-mode/issues/527): Fix `clojure-sort-ns` mangling `:gen-class` and other non-sortable ns forms.
+* [#619](https://github.com/clojure-emacs/clojure-mode/issues/619): Fix `clojure-thread-last-all` breaking forms containing line comments by absorbing closing parens into comments.
 * Fix typos in `clojure-mode-extra-font-locking`: `halt-when?` -> `halt-when`, `simple-indent?` -> `simple-ident?`.
 * Fix `doc` and `find-doc` misplaced under `clojure.core` instead of `clojure.repl` in extra font-locking.
 

clojure-mode.el

@@ -2685,7 +2685,13 @@ With universal argument \\[universal-argument], fully unwind thread."
       (clojure--remove-superfluous-parens)
       ;; cljr #255 Fix dangling parens
       (forward-sexp)
-      (when (looking-back "^\\s-*\\()+\\)\\s-*" (line-beginning-position))
+      (when (and (looking-back "^\\s-*\\()+\\)\\s-*" (line-beginning-position))
+                 ;; Don't join if previous line ends in a comment,
+                 ;; as that would absorb the parens into the comment.
+                 (not (save-excursion
+                        (forward-line -1)
+                        (end-of-line)
+                        (nth 4 (syntax-ppss)))))
         (let ((pos (match-beginning 1)))
           (put-text-property pos (1+ pos) 'clojure-thread-line-joined t))
         (join-line))

test/clojure-mode-refactor-threading-test.el

@@ -379,6 +379,18 @@
      (comp (serve))
      (deftask dev []))"
 
+    (beginning-of-buffer)
+    (clojure-thread-last-all nil))
+
+  (when-refactoring-it "should preserve line comments"
+    "(foo x ;; grobble
+  (bar y))"
+
+    "(->> y
+     bar
+     (foo x ;; grobble
+          ))"
+
     (beginning-of-buffer)
     (clojure-thread-last-all nil)))