close #2386: throw a warning when chunk options are duplicated in both chunk header and pipe comments

Author: yihui

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: knitr
 Type: Package
 Title: A General-Purpose Package for Dynamic Report Generation in R
-Version: 1.49.2
+Version: 1.49.3
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "xie@yihui.name", comment = c(ORCID = "0000-0003-0645-5666")),
     person("Abhraneel", "Sarma", role = "ctb"),

NEWS.md

@@ -1,5 +1,9 @@
 # CHANGES IN knitr VERSION 1.50
 
+## MINOR CHANGES
+
+- A warning will be issued when chunk options are duplicated in both the chunk header and pipe comments (thanks, @cderv, #2386). A chunk option should appear in only one of these places.
+
 # CHANGES IN knitr VERSION 1.49
 
 ## NEW FEATURES

R/parser.R

@@ -113,10 +113,16 @@ parse_block = function(code, header, params.src, markdown_mode = out_format('mar
   # merge with possible chunk options written as (YAML or CSV) metadata in
   # chunk, and remove metadata from code body
   parts = partition_chunk(engine, code)
+  dup = intersect(names(params), names(parts$options))
   params = merge_list(params, parts$options)
-  code = parts$code
+  label = params$label
+  if (length(dup)) warning(
+    "Duplicated chunk option(s) ", paste0("'", dup, "'", collapse = ', '),
+    " in both chunk header and pipe comments of the chunk '", label, "'.", call. = FALSE
+  )
 
-  label = params$label; .knitEnv$labels = c(.knitEnv$labels, label)
+  code = parts$code
+  .knitEnv$labels = c(.knitEnv$labels, label)
   if (length(code) || length(params[['file']]) || length(params[['code']])) {
     if (label %in% names(knit_code$get())) {
       if (identical(getOption('knitr.duplicate.label'), 'allow')) {