Support alt text for images in LaTeX output

NEWS.md

@@ -4,6 +4,8 @@
 
 - In-chunk references of the form `<<label>>` can be disabled via the chunk option `ref.chunk = FALSE` now (thanks, @jennybc @gadenbuie, #2360).
 
+- Added support for `fig.alt` for LaTeX output, i.e., using `\includegraphics[alt={alt text}]` (thanks, @capnrefsmmat, #2378).
+
 ## BUG FIXES
 
 - In-chunk references of the form `<<label>>` should not be resolved if `label` is not found in the document (thanks, @jennybc @gadenbuie, #2360).

R/hooks-latex.R

@@ -162,9 +162,10 @@ hook_plot_tex = function(x, options) {
   # maxwidth does not work with animations
   if (animate && identical(ow, '\\maxwidth')) ow = NULL
   if (is.numeric(ow)) ow = paste0(ow, 'px')
-  size = paste(c(sprintf('width=%s', ow),
-                 sprintf('height=%s', options$out.height),
-                 options$out.extra), collapse = ',')
+  size = paste(c(
+    sprintf('width=%s', ow), sprintf('height=%s', options$out.height),
+    sprintf('alt={%s}', escape_percent(options$fig.alt)), options$out.extra
+  ), collapse = ',')
 
   paste0(
     fig1, align1, sub1, resize1,

tests/testit/test-hooks-latex.R

@@ -0,0 +1,17 @@
+library(testit)
+
+assert("alt text is included in LaTeX output", {
+  # no alt text
+  (hook_plot_tex('foo.pdf', list(fig.align = 'center', fig.show = 'asis')) %==%
+     '\n\n{\\centering \\includegraphics{foo} \n\n}\n\n')
+
+  # alt text
+  (hook_plot_tex('foo.pdf', list(fig.alt = 'Alt', fig.align = 'center',
+                                 fig.show = 'asis')) %==%
+     '\n\n{\\centering \\includegraphics[alt={Alt}]{foo} \n\n}\n\n')
+
+  # with width
+  (hook_plot_tex('foo.pdf', list(fig.alt = 'Alt', fig.align = 'center',
+                                 fig.show = 'asis', out.width = '\\maxwidth')) %==%
+     '\n\n{\\centering \\includegraphics[width=\\maxwidth,alt={Alt}]{foo} \n\n}\n\n')
+})