(scan-error "Containing expression ends prematurely" 2 2)

[DamienCassou]

1. M-: (helpful-variable 'magit-branch-popup)

Debugger entered--Lisp error: (scan-error "Containing expression ends prematurely" 2 2)
  scan-sexps(4 -1)
  forward-sexp(-1)
  calculate-lisp-indent((1 2 13 nil nil nil 0 nil nil (2) nil))
  lisp-indent-line()
  cl--do-prettyprint()
  cl-prettyprint((:variable magit-branch-arguments :man-page "git-branch" :variables #f(compiled-function () #<bytecode 0x1b1dbe1>) :actions ((98 "Checkout" magit-branch-or-checkout) nil (67 "Configure..." magit-branch-config-popup) (108 "Checkout local branch" magit-branch-checkout) (115 "Create new spin-off" magit-branch-spinoff) (109 "Rename" magit-branch-rename) (99 "Checkout new branch" magit-branch-and-checkout) (110 "Create new branch" magit-branch) (120 "Reset" magit-branch-reset) (119 "Checkout new worktree" magit-worktree-checkout) (87 "Create new worktree" magit-worktree-branch) (107 "Delete" magit-branch-delete) (106 "Create branch from jira" magit-create-branch-from-jira-issue)) :default-action magit-checkout :max-action-columns 3 :setup-function magit-branch-popup-setup))
  helpful--pretty-print((:variable magit-branch-arguments :man-page "git-branch" :variables #f(compiled-function () #<bytecode 0x1b1dbe1>) :actions ((98 "Checkout" magit-branch-or-checkout) nil (67 "Configure..." magit-branch-config-popup) (108 "Checkout local branch" magit-branch-checkout) (115 "Create new spin-off" magit-branch-spinoff) (109 "Rename" magit-branch-rename) (99 "Checkout new branch" magit-branch-and-checkout) (110 "Create new branch" magit-branch) (120 "Reset" magit-branch-reset) (119 "Checkout new worktree" magit-worktree-checkout) (87 "Create new worktree" magit-worktree-branch) (107 "Delete" magit-branch-delete) (106 "Create branch from jira" magit-create-branch-from-jira-issue)) :default-action magit-checkout :max-action-columns 3 :setup-function magit-branch-popup-setup))
  helpful-update()
  helpful-variable(magit-branch-popup)
  eval((helpful-variable 'magit-branch-popup) nil)
  eval-expression((helpful-variable 'magit-branch-popup) nil nil 127)
  funcall-interactively(eval-expression (helpful-variable 'magit-branch-popup) nil nil 127)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)

[Wilfred]

This is a bug with calculate-lisp-indent, which helpful--pretty-print calls via cl-prettyprint. If you have a sufficiently large list literal, e.g.

(:variable magit-branch-arguments :man-page "git-branch" :actions
           ((98 "Checkout" magit-checkout)
            (110 "Create new branch" magit-branch)
            (67 "Configure..." magit-branch-config-popup)
            (99 "Checkout new branch" magit-branch-and-checkout)
            (115 "Create new spin-off" magit-branch-spinoff)
            (109 "Rename" magit-branch-rename)
            (119 "Checkout new worktree" magit-worktree-checkout)
            (87 "Create new worktree" magit-worktree-branch)
            (120 "Reset" magit-branch-reset)
            nil nil
            (107 "Delete" magit-branch-delete)
            (102 "new branch From current" wh/magit-branch-from-current-and-checkout))
           :default-action magit-checkout :max-action-columns 3 :setup-function magit-branch-popup-setup)
;; or
(:foo foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo :bar bar)

Then cl-prettyprint adds newlines, splitting the list over multiple lines. It looks like lisp-indent-line can't handle code of the form:

(:foo foo
 :bar bar)

If you put point on the second line and call calculate-lisp-indent. you get the same error.

[Wilfred]

Turns out it was a bug with helpful.el not using the right major mode. This should work now.