fix #424: if the error "Undefined control sequence" comes from l3back…

…end, let tinytex try to reinstall l3backend, which will trigger `tlmgr_update()` that runs `fmtutil-sys` to fix the L3 programming layer mismatch issue (although 5946a2a has guarded against it)

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: tinytex
 Type: Package
 Title: Helper Functions to Install and Maintain TeX Live, and Compile LaTeX Documents
-Version: 0.48.1
+Version: 0.48.2
 Authors@R: c(
   person("Yihui", "Xie", role = c("aut", "cre", "cph"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
   person(given = "Posit Software, PBC", role = c("cph", "fnd")),

R/latex.R

@@ -590,6 +590,10 @@ regex_errors = function() {
       # when a required tikz library is missing
       '.* (tikzlibrary[^ ]+?[.]code[.]tex).*'
     ),
+    l3backend = c(
+      # L3 programming layer mismatch (#424)
+      '^File: ([^ ]+) \\d{4,}-\\d{2}-\\d{2} .*$'
+    ),
     style = c(
       # missing .sty or commands
       ".* Loading '([^']+)' aborted!",
@@ -614,6 +618,11 @@ detect_files = function(text) {
     v = grep_sub(p, '\\1', x)
     if (length(v) == 0) return(v)
     if (p == r$tikz && length(grep('! Package tikz Error:', text)) == 0) return()
+    # if the problem is caused by the L3 programming layer mismatch, use the
+    # last found file before the error line, which should be from l3backend
+    if (p == r$l3backend) return(
+      if (length(grep('^! Undefined control sequence', text)) > 0) tail(v, 1)
+    )
     # these are some known filenames
     for (i in c('epstopdf', grep('[.]', names(r), value = TRUE))) {
       if (p %in% r[[i]]) return(i)