Latex backend/package bug: `! Package array Error: Empty preamble: 'l' used.`

[Andre Knispel]

Here's a literate Agda file that LaTeX doesn't like:

\documentclass{article}
\usepackage{agda}

\begin{document}
\begin{AgdaMultiCode}
\begin{code}
module Latex-Bug where
open import Data.Bool
open import Function

ff : Bool
ff = true
  where
  f1 : Bool
  f1 = case true of
\end{code}
\begin{code}[hide]
    λ where
\end{code}
\begin{code}
      _ → true

  f2 : Bool
  f2 = case true of
\end{code}
\begin{code}[hide]
    λ where
\end{code}
\begin{code}
    _ → true
\end{code}
\end{AgdaMultiCode}
\end{document}

Changing pretty much anything will make this not fail. For example renaming ff to f or indenting the last line of f3 (_ → true) by two more spaces. Even the two [hide] modifiers cannot be removed.

The sequence of commands I'm using to compile this is:

agda --latex Latex-Bug.lagda && cd latex && latexmk -xelatex -halt-on-error Latex-Bug.tex

The error message I'm getting is the following:

! Package array Error: Empty preamble: `l' used.

See the array package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              
                                                  
l.43 \end{code}
               
No pages of output.

[Andreas Abel]

Here is a version without the standard library:

\documentclass{article}
\usepackage{agda}

\begin{document}
\begin{AgdaMultiCode}
\begin{code}
case_of_ : {A B : Set} (a : A) (f : A → B) → B
case a of f = f a
open import Agda.Builtin.Bool -- needed in this block before the ff

ff : Bool
ff = true
  where
  f1 : Bool
  f1 = case true of
\end{code}
\begin{code}[hide]
    λ where
\end{code}
\begin{code}
      _ → true

  f2 : Bool
  f2 = case true of
\end{code}
\begin{code}[hide]
    λ where
\end{code}
\begin{code}
    _ → true
\end{code}
\end{AgdaMultiCode}
\end{document}

It does not depend on -xelatex.

[Andreas Abel]

Shrank the generated latex file to this:

\documentclass{article}
\usepackage{agda}
\begin{document}
\begin{AgdaMultiCode}
%% The column names must be different, e.g foo/bar/baz
\begin{code}
\\ %% needed
\>[foo]
\end{code}
\begin{code}
\>[bar]
\end{code}
\begin{code}
\>[baz]
\end{code}
\end{AgdaMultiCode}
\end{document}

The AgdaMultiCode environment can be removed by declaring \setboolean{Agda@Align}{true} instead.

[Andreas Abel]

Shrinking away agda.sty I arrive at this polytable reproducer (still same error):

\documentclass{article}
\RequirePackage{polytable}
\defaultcolumn{l}
\begin{document}
%% The column names must be different
\begin{pboxed}\savecolumns
\\ %% needed
\>[foo]
\end{pboxed}
\begin{pboxed}\restorecolumns
\>[bar]
\end{pboxed}
\begin{pboxed}\restorecolumns
\>[baz]
\end{pboxed}
\end{document}

[Andreas Abel]

This might be an issue in polytable rather than in agda.sty. I reported this upstream:

• kosmikus/lhs2tex#104