close #2376: no-op on invalid dependson values, and issue a warning

NEWS.md

@@ -26,6 +26,8 @@
 
 - If a character value is passed to the chunk option `message` or `warning`, it will be coerced by `as.logical()`, e.g., a character string `"NA"` will be coerced to `NA` (thanks, @cderv, #2375).
 
+- Issue a warning when the chunk option `dependson` receives an invalid value (thanks, @otoomet, #2376).
+
 - Changed the format of the reference card from PDF to HTML so building this package will not require LaTeX. See `vignette('knitr-refcard', package = 'knitr')`.
 
 - Switched the vignette engine from **knitr** to `litedown::vignette` for some package vignettes.

R/parser.R

@@ -137,8 +137,9 @@ parse_block = function(code, header, params.src, markdown_mode = out_format('mar
       deps[deps < 0] = length(.knitEnv$labels) + deps[deps < 0]
       deps = .knitEnv$labels[deps[deps > 0]]
     }
-    for (i in deps)
-      dep_list$set(setNames(list(c(dep_list$get(i), label)), i))
+    if (is.character(deps)) {
+      for (i in deps) dep_list$set(setNames(list(c(dep_list$get(i), label)), i))
+    } else warning2("Invalid chunk option 'dependson' (must be character or numeric)")
   }
 
   # for quarto only