Implement LaTeX footnotes using \footnotemark and \footnotetext (#32)

* use \footnotetext and \footnotemark to implement LaTeX footnotes

* git diff be62b2b c3be50e > src/patches/latex-footnotes.diff

* add tests, news, and bump version

---------

Co-authored-by: Jeroen Ooms <[email protected]>

Author: yihui

NEWS

@@ -1,6 +1,7 @@
 2.0.0
   - The tagfilter extension for markdown_html now actually works (#15)
   - Backport patch to filter illegal control characters in markdown_xml()
+  - Implement LaTeX footnotes (#32)
 
 1.9.5
   - Fix parallel make problem

src/cmark/latex.c

@@ -447,8 +447,20 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_FOOTNOTE_DEFINITION:
+    if (entering) {
+      LIT("\\footnotetext[");
+      OUT(cmark_chunk_to_cstr(renderer->mem, &node->as.literal), false, LITERAL);
+      LIT("]{");
+    } else {
+      LIT("}");
+    }
+    break;
   case CMARK_NODE_FOOTNOTE_REFERENCE:
-    // TODO
+    if (entering) {
+      LIT("\\footnotemark[");
+      OUT(cmark_chunk_to_cstr(renderer->mem, &node->parent_footnote_def->as.literal), false, LITERAL);
+      LIT("]");
+    }
     break;
 
   default:

src/patches/apply.sh

@@ -2,4 +2,5 @@
 
 # Upstream PR: https://github.com/github/cmark-gfm/pull/362
 patch -p2 -d ../cmark < 362.diff
-
+# Support footnotes for LaTeX: https://github.com/r-lib/commonmark/pull/32
+patch -p2 -d ../cmark < latex-footnotes.diff

src/patches/latex-footnotes.diff

@@ -0,0 +1,26 @@
+diff --git a/src/cmark/latex.c b/src/cmark/latex.c
+index 1a6367a..5fab7ee 100644
+--- a/src/cmark/latex.c
++++ b/src/cmark/latex.c
+@@ -447,8 +447,20 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
+     break;
+ 
+   case CMARK_NODE_FOOTNOTE_DEFINITION:
++    if (entering) {
++      LIT("\\footnotetext[");
++      OUT(cmark_chunk_to_cstr(renderer->mem, &node->as.literal), false, LITERAL);
++      LIT("]{");
++    } else {
++      LIT("}");
++    }
++    break;
+   case CMARK_NODE_FOOTNOTE_REFERENCE:
+-    // TODO
++    if (entering) {
++      LIT("\\footnotemark[");
++      OUT(cmark_chunk_to_cstr(renderer->mem, &node->parent_footnote_def->as.literal), false, LITERAL);
++      LIT("]");
++    }
+     break;
+ 
+   default:

tests/testthat/test-extensions.R

@@ -42,6 +42,20 @@ test_that("autolink", {
 
 })
 
+
+test_that("footnotes", {
+  # a single footnote
+  md <- "Hello[^1]\n\n[^1]: A footnote."
+  expect_equal(markdown_latex(md, footnotes = FALSE), "Hello{[}\\^{}1{]}\n\n{[}\\^{}1{]}: A footnote.\n")
+  expect_equal(markdown_latex(md, footnotes = TRUE), "Hello\\footnotemark[1]\n\n\\footnotetext[1]{A footnote.\n\n}\n")
+
+  # multiple footnotes
+  md <- "Hello[^1] World[^foo-2]\n\n[^1]: A footnote.\n\n[^foo-2]: Footnote ID does not have to be a number."
+  expect_equal(markdown_latex(md, footnotes = FALSE), "Hello{[}\\^{}1{]} World{[}\\^{}foo-2{]}\n\n{[}\\^{}1{]}: A footnote.\n\n{[}\\^{}foo-2{]}: Footnote ID does not have to be a number.\n")
+  expect_equal(markdown_latex(md, footnotes = TRUE), "Hello\\footnotemark[1] World\\footnotemark[foo-2]\n\n\\footnotetext[1]{A footnote.\n\n}\\footnotetext[foo-2]{Footnote ID does not have to be a number.\n\n}\n")
+})
+
+
 test_that('tagefilter', {
   input <- "<title><style></style></title>\n"
   expect_equal(input, markdown_html(input))