Problems highlighting of incorrect code:

Fix by adding highlight=FALSE to chunks.

Getting the following error now wiht current version of knitr:
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label: wrong (with options)
List of 1
 $ eval: logi FALSE

Warning in block_exec(params) :
  failed to tidy R code in chunk <wrong>
reason: Error in parse(text = x, keep.source = TRUE) :
  <text>:3:0: unexpected end of input
1: x <- (1 + (2 * 3)
2: +
 ^

Error in parse(text = code) : <text>:3:0: unexpected end of input
1: x <- (1 + (2 * 3)
2: +
 ^
Warning in highr::hilight(x, format, prompt = options$prompt) :
  the syntax of the source code is invalid; the fallback mode is used
Quitting from lines 1024-1026 (spr.Rnw)
Error in parse(text = piece) : <text>:3:0: unexpected end of input
1: x <- (1 + (2 * 3)
2: +
 ^
Calls: knit2pdf ... hilight_source -> <Anonymous> -> group_src -> parse

Execution halted
make: *** [spr] Error 1
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