Insure fontawesome V4 compatibility in navbar (#1994)

This allows to have old navbar definition to work with new FA5 also. It was a breaking change previously to this. 

Co-authored-by: Yihui Xie <[email protected]>

NEWS.md

@@ -5,6 +5,8 @@ rmarkdown 2.9
 
 - Floating ToC in `html_document` can now hide headings with unnumbered and unlisted classes (thanks, @atusy, #1993).
 
+- Fix prefix handling in R Markdown website's navbar for Fontawesome V5 and compatibility with V4. For icon only available in V5, the full prefix + name should be use, especially with new `fab` prefix (e.g. `fab fa-r-project`). If no prefix is used (e.g `fa-home` instead of `fas fa-home`), the `fa` prefix will be added for V4 compatibility as it has been deprecated in V5. We advice to use the full prefix + name for icons following Fontawesome documentation. (#1994)
+
 - `rmarkdown::site_generator()` can hang session waiting for input when the `site` field is not found in the YAML frontmatter of `index.Rmd` (thanks, @kevinushey @mirh, #2043).
 
 

R/html_dependencies.R

@@ -222,7 +222,7 @@ navbar_icon_dependencies <- function(navbar) {
   source <- read_utf8(navbar)
 
   # find icon references
-  res <- regexec('<(span|i) +class *= *("|\') *(fa\\w fa|ion ion)-', source)
+  res <- regexec('<(span|i) +class *= *("|\') *(fa\\w? fa|ion ion)-', source)
   matches <- regmatches(source, res)
   libs <- c()
   for (match in matches) {
@@ -232,7 +232,7 @@ navbar_icon_dependencies <- function(navbar) {
   libs <- unique(libs)
 
   # return their dependencies
-  any_fa <- any(grepl("fa\\w fa", libs))
+  any_fa <- any(grepl("fa\\w? fa", libs))
   any_ion <- any(grepl("ion ion", libs))
   html_dependencies_fonts(any_fa, any_ion)
 }

R/html_document.R

@@ -652,15 +652,18 @@ navbar_link_text <- function(x, ...) {
       iconset <- split[[1]][[1]]
     else
       iconset <- ""
-    # check if a full class is passed for fontawesome
-    # use default 'fas' otherwise
+    # check if a full class is passed for fontawesome = V5
+    # Add fa deprecated fa prefix otherwise = V4 compatibility
     # https://github.com/rstudio/rmarkdown/issues/1554
-    class = if (grepl("^fa\\w fa", iconset)) {
+    class = if (grepl("^fa\\w? fa", iconset)) {
+      # Fontawesome 5 - full new prefix + name must be passed
+      # if old fa prefix is passed - keep it for compatibility
       x$icon
     } else if (iconset == "fa") {
-      paste("fas", x$icon)
+      # Fontawesome 4 compatibility - Add deprecated fa prefix
+      paste("fa", x$icon)
     } else {
-      # should be other than FontAwesome
+      # Other Icon sets
       paste(iconset, x$icon)
     }
     tagList(tags$span(class = class), " ", x$text, ...)