Infer bib engine from file contents

.gitignore

@@ -2,3 +2,11 @@
 .Rhistory
 .RData
 .Ruserdata
+
+*.aux
+*.bbl
+*.blg
+*.bcf
+*.log
+*.run.xml
+

.travis.yml

@@ -1,5 +1,6 @@
 language: r
 sudo: false
+latex: false
 cache: packages
 
 env:

R/latex.R

@@ -21,8 +21,15 @@
 #' @param file A LaTeX file path.
 #' @param engine A LaTeX engine (can be set in the global option
 #'   \code{tinytex.engine}, e.g., \code{options(tinytex.engine = 'xelatex')}).
-#' @param bib_engine A bibliography engine (can be set in the global option
+#' @param bib_engine A bibliography engine, one of \code{'bibtex'} and
+#'   \code{'biber'} (can be set in the global option
 #'   \code{tinytex.bib_engine}).
+#'   If missing, the engine is inferred from the contents of \code{file}: if
+#'   the file contains \verb{\addbibresource} then the engine is assumed to
+#'   be \code{'biber'} unless \verb{backend=biber} occurs in the optional argument
+#'   to \code{biblatex}, provided the package occurs on one line. Otherwise,
+#'   the engine is assumed to be \code{'bibtex'} if \verb{\bibliography}
+#'   is present in \code{file}.
 #' @param engine_args Command-line arguments to be passed to \code{engine} (can
 #'   be set in the global option \code{tinytex.engine_args}, e.g.,
 #'   \code{options(tinytex.engine_args = '-shell-escape'}).
@@ -57,7 +64,26 @@ latexmk = function(
     }
   }
   if (missing(max_times)) max_times = getOption('tinytex.compile.max_times', max_times)
-  if (missing(bib_engine)) bib_engine = getOption('tinytex.bib_engine', bib_engine)
+  if (missing(bib_engine)) {
+    if (is.null(getOption('tinytex.bib_engine'))) {
+      file_lines = sub('(?<!(\\\\))[%].*$', '%', readLines(file), perl = TRUE)
+      if (any(grepl('\\addbibresource{', file_lines, fixed = TRUE))) {
+        if (any(grepl('\\\\usepackage\\[[^\\]]*backend\\s*[=]\\s*bibtex.*\\{biblatex\\}',
+                      file_lines,
+                      perl = TRUE))) {
+          bib_engine = 'bibtex'
+        } else {
+          bib_engine = 'biber'
+        }
+      } else if (any(grepl('\\bibliography{', file_lines, fixed = TRUE))) {
+        bib_engine = 'bibtex'
+      } else {
+        bib_engine = NULL
+      }
+    } else {
+      bib_engine = getOption('tinytex.bib_engine')
+    }
+  }
   if (missing(engine_args)) engine_args = getOption('tinytex.engine_args', engine_args)
   owd = setwd(dirname(file))
   on.exit(setwd(owd), add = TRUE)

tests/test-travis/bib-inference/backend-bibtex-a.bib

@@ -0,0 +1,8 @@
+@Manual{R-base,
+  title = {R: A Language and Environment for Statistical Computing},
+  author = {{R Core Team}},
+  organization = {R Foundation for Statistical Computing},
+  address = {Vienna, Austria},
+  year = {2016},
+  url = {https://www.R-project.org/},
+}

tests/test-travis/bib-inference/backend-bibtex-expected.txt

@@ -0,0 +1,13 @@
+      R Core Team [1].
+
+
+References
+[1]    R Core Team. R: A Language and Environment for Statistical Comput-
+       ing. R Foundation for Statistical Computing. Vienna, Austria, 2016. url:
+       https://www.R-project.org/.
+
+
+
+
+                                        1
+

tests/test-travis/bib-inference/backend-bibtex.tex

@@ -0,0 +1,9 @@
+\documentclass{article}
+\usepackage[backend=bibtex]{biblatex}
+\addbibresource{backend-bibtex-a}
+
+\begin{document}
+\textcite{R-base}.
+\printbibliography
+\end{document}
+

tests/test-travis/bib-inference/the-biber.tex

@@ -0,0 +1,9 @@
+\documentclass{article}
+\usepackage{biblatex}
+
+\addbibresource{backend-bibtex-a.bib}
+
+\begin{document}
+\textcite{R-base}.
+\printbibliography
+\end{document}

tests/test-travis/test-bib_inference.R

@@ -0,0 +1,43 @@
+library(testit)
+
+if (Sys.which("pdflatex") == "") {
+  tinytex::install_tinytex()
+}
+
+assert("Bibtex inference", {
+  current_wd = getwd()
+  on.exit(setwd(current_wd), add = TRUE)
+  setwd("bib-inference")
+
+
+	first_res = is.null(pdflatex("backend-bibtex.tex")) &&
+	if (nzchar(Sys.which('pdftotext'))) {
+	  system('pdftotext -layout backend-bibtex.pdf')
+	  backend_bibtex_text = readLines('backend-bibtex.txt', n = 8L, warn = FALSE)
+	  backend_bibtex_expected = readLines('backend-bibtex-expected.txt', n = 8L, warn = FALSE)
+	  setwd(current_wd)
+	  identical(backend_bibtex_text,
+	            backend_bibtex_expected)
+	} else {
+	  setwd(current_wd)
+	  TRUE  # skip test
+	}
+})
+
+assert("Biber inference", {
+  current_wd = getwd()
+  on.exit(setwd(current_wd), add = TRUE)
+  setwd("bib-inference")
+  first_res = is.null(pdflatex("the-biber.tex")) &&
+    if (nzchar(Sys.which('pdftotext'))) {
+      system('pdftotext -layout the-biber.pdf')
+      backend_bibtex_text = readLines('the-biber.txt', n = 8L, warn = FALSE)
+      backend_bibtex_expected = readLines('backend-bibtex-expected.txt', n = 8L, warn = FALSE)
+      setwd(current_wd)
+      identical(backend_bibtex_text,
+                backend_bibtex_expected)
+    } else {
+      setwd(current_wd)
+      TRUE  # skip test
+    }
+})