Leading tabs in code block are not retained in org reader with -p

[minyez]

Explain the problem.
I tried to convert an org-mode file to Markdown. When using pandoc with -p option to preserve the tabs in the Makefile source block, I found the leading tab is converted to single space while the other tabs remain unexpanded.

Minimal example

$ cat example.org
#+begin_src makefile
%.o: %.cpp
	$(CXX)	-o	$@	$<
#+end_src

There is a leading tab and tabs between entries in the directive. When converted to markdown with and without -p

$ pandoc -f org -t json -p example.org
{"pandoc-api-version":[1,23,1],"meta":{},"blocks":[{"t":"CodeBlock","c":[["",["makefile"],[]],"%.o: %.cpp\n $(CXX)\t-o\t$@\t$<\n"]}]}
$ pandoc -f org -t json example.org
{"pandoc-api-version":[1,23,1],"meta":{},"blocks":[{"t":"CodeBlock","c":[["",["makefile"],[]],"%.o: %.cpp\n    $(CXX)  -o  $@  $<\n"]}]}

On the other hand, the markdown reader seems fine (I don't know how to make markdown block within a code block correctly rendered, so I added a comma before backticks)

$ cat example.md
,```makefile
%.o: %.cpp
	$(CXX)	-o	$@	$<
,```
$ pandoc -f markdown -t json -p example.md
{"pandoc-api-version":[1,23,1],"meta":{},"blocks":[{"t":"CodeBlock","c":[["",["makefile"],[]],"%.o: %.cpp\n\t$(CXX)\t-o\t$@\t$<"]}]}
$ pandoc -f markdown -t json example.md
{"pandoc-api-version":[1,23,1],"meta":{},"blocks":[{"t":"CodeBlock","c":[["",["makefile"],[]],"%.o: %.cpp\n    $(CXX)  -o  $@  $<"]}]}

Expected behavior

$ pandoc -f org -t json -p example.org
{"pandoc-api-version":[1,23,1],"meta":{},"blocks":[{"t":"CodeBlock","c":[["",["makefile"],[]],"%.o: %.cpp\n\t$(CXX)\t-o\t$@\t$<\n"]}]}

Pandoc version?
pandoc is installed using homebrew on macOS Sonoma

$ pandoc --version
pandoc 3.3
Features: +server +lua
Scripting engine: Lua 5.4

[tarleb]

Pandoc's behavior is consistent with that of the Emacs org-mode exporters as far as I can tell. Is there an Org-mode option that would allow to preserve tabs when exporting?

[minyez]

Hi @tarleb as far as I know there is no org-export variable directly related to tab, but there is a variable called org-src-preserve-indentation to control how to handle code block indentation on export. When it is nil, the minimum leading whitespace characters (including tabs) are removed and the code lines are re-indented. When non-nil, the leading characters are preserved.

For the current example, I use org-export to do an org-to-org conversion. Emacs is run with emacs -Q. When org-src-preserve-indentation is t

#+begin_src makefile
%.o: %.cpp
	$(CXX)	-o	$@	$<
#+end_src

All tabs are retained. When org-src-preserve-indentation is nil

#+begin_src makefile
  %.o: %.cpp
          $(CXX)	-o	$@	$<
#+end_src

It replaces the leading tab with 8 white spaces, and add 2 spaces on both lines (the number of spaces depends on another variable). The other tabs are preserved.

[tarleb]

Interesting, thanks. If I understand correctly, then setting org-src-preserve-indentation to a non-nil value is equivalent to adding the -i flag to all src blocks.

In principle, it should be enough to add the -i flag to the src block while also calling pandoc with the -p command line flag.

#+begin_src makefile -i
%.o: %.cpp
	$(CXX)	-o	$@	$<
#+end_src

However, it seems that the leading tab is currently lost and converted to a single space. I'm therefore re-adding the bug label.

[minyez]

Thanks for your infomation, I was never aware of the capability to add this kind of flag to src block. I tried just now but didn't find any difference when exporting it. Did I miss something?

$ cat example.org
#+begin_src makefile -i
%.o: %.cpp
	$(CXX)	-o	$@	$<
#+end_src
$ pandoc -f org -t json -p example.org
{"pandoc-api-version":[1,23,1],"meta":{},"blocks":[{"t":"CodeBlock","c":[["",["makefile"],[]],"%.o: %.cpp\n $(CXX)\t-o\t$@\t$<\n"]}]}

[tarleb]

Exactly, that's the bug, and it should be fixed now. Please try the next nightly built, which should become available in about 15 hours.

[minyez]

I will try then, thanks a lot for the quick fix! A remaining question is: is the -i flag the same as the one of pandoc CLI, i.e. -i/--incremental?

The reason I am asking is that there seems no way to retain -i-type source block flags when doing an org-to-org export, which is necessary when using ox-pandoc for conversion. So I would prefer using a command line flag similar to -i-type flag for certain source block. Sorry I was completely wrong. -i is retained in org-to-org export.

[tarleb]

The -i flag of the pandoc CLI and of orgmode src blocks are entirely separate; they only incidentally share the same characters.

[minyez]

Thanks for clarification, I understand now it is a orgmode src block flag rather than a pandoc one. I was only aware of head arguments starting with :. Could you please maybe share your knowledge of similar - flags, or direct me to some documentation? I searched the "16 Working with Source Code" section of org-mode manual, but found nothing relevant.

[tarleb]

E.g. https://orgmode.org/manual/Literal-Examples.html
But pandoc supports only a subset of those.