With a new release of the evaluate package (v0.19) last week, the meanings
of the chunk option message = FALSE and warning = FALSE in knitr have
changed. Previously, they meant that messages and warnings would not be captured
at all. Normally the messages would be sent to the console.
That was both confusing and inconvenient. When users set message = FALSE, the
more likely intention is “I’m sure I don’t want to see any messages anywhere
from this code chunk”, instead of “I don’t want to see messages in the output
document but want to see them in the console”.
If you have updated the evaluate package, message = FALSE will completely
suppress messages, and similarly, warning = FALSE will muffle all warnings in
a code chunk. For example, this will just suppress the package startup messages:
```{r, message=FALSE}
library(dplyr)
```
You no longer have to resort to functions such as suppressMessages() or
suppressWarnings() in your code like this:
```{r, message=FALSE}
suppressPackageStartupMessages(library(dplyr))
```
I’m not sure if there are any users who actually prefer the old behavior. If you
do want messages in the console, please set the chunk option message = NA
(similarly, warning = NA for warnings).
P.S. One motivation behind this change was to make knitr’s text progress bar cleaner. With the next version of knitr, you will see a single-line progress bar, which will not be interrupted by messages in code chunks. Currently you can try out the development version of knitr (the CRAN release will come in January next year). Please also let me know if you have any feedback on knitr’s new progress bar.