[SOLVED] Cannot Parse YAML Header in flexdashboard

Cannot Parse YAML Header in flexdashboard

While this works as expected (adding the Date on the right hand side of the navbar):

---
output:
  flexdashboard::flex_dashboard:
    orientation: rows
    theme:
      version: 3
      bootswatch: flatly
    vertical_layout: fill
    navbar:
        - title: !expr Sys.Date()
          href: "#"
          align: right
---

this one fails (unnecessary code stripped), and I have no idea why, given that both !expr bits are valid R code, which work when pasted manually to the console.

    navbar:
        - title: !expr format(Sys.Date(), "Created on: %Y-%m-%d")
          href: "#"
          align: right

The latter throws the following error:

Error in yaml::yaml.load(..., eval.expr = TRUE) : Could not parse expression: format(Sys.Date(), "Created on Calls: ... parse_yaml_front_matter -> yaml_load -> Execution halted

Solution

It seems that the colon followed by a whitespace : is the culprit. Removing this space renders the document just fine. This seeme like a bug, or at least an undocumented restriction. For now I found an hack by replacing the colon by its Unicode representation:

   navbar:
      - title: !expr format(Sys.Date(),"Created on\U003A %Y-%m-%d")