YAML parameters being interpreted as R and giving unhelpful error messages

[plukethep]

Bug description

I believe you can put R commands into chunk paramters, this is useful but does give issues when you miss out a space. E.g.

---
title: "test"
---

```{r}
#| warning: false
#| eval:false
```

Which gives the error:

processing file: test.rmarkdown
Error in yaml::yaml.load(yaml, eval.expr = TRUE) :
Scanner error: while scanning a simple key at line 2, column 1 could not find expected ':' at line 3, column 1
Calls: .main ... parse_block -> partition_yaml_options ->
Execution halted

I presume that this is because the eval:false line is being interpreted as R rather than YAML, but the error message isn't helpful and had me messing with the top YAML as it didn't mention when code chunk it was referring to.

Strangely, dropping the warning line fixes things:

---
title: "test"
---

```{r}
#| eval:false
```

RStudio: 2022.02.3 Build 492
Windows

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[cscheid]

Thanks for reporting! I agree that this is definitely annoying behavior. Unfortunately, fixing this is very hard in general, and it would involve writing a new YAML parser that is more tolerant of errors. We actually already use two separate parsers in part to handle some errors, but this one slips through.

The issue here is that eval:false is a valid YAML object, namely the string "eval:false". And so is eval: false, namely the JSON object {"eval": false}. But

warning: false
eval:false

is not valid yaml because the string scalar eval:false appears in a wrong context. Unfortunately, neither of the parsers we use catch this common mistake.

We hear, you though, and we need to provide better guidance somehow. Our plan is to add something like a quarto lint command that catches these potential mistakes without having to run a parser or validator. We are planning a 1.0 release and won't have time to add the linter to 1.0, but stay tuned for it in the future.