Compiler crash `invalid content in tag union variable ...`

[OBenjaminT]

I was messing around with some roc code (I'm very new to this) in the zig example and the compiler crashed.

app "rocLovesZig"
    packages { pf: "main.roc" }
    imports []
    provides [main] to pf

main : Str
main =  RenderTree Node Data {text: "Ziggy Data!"}

RenderTree : Node -> Str
RenderTree = \node ->
    when node is
        Data load ->
            """
            \(load.text)
            """
        Link load ->
            """
            """
        Tag load ->
            """
            """

DataLoad : {text: Str}

LinkLoad : {}

TagLoad : {}

Node : [
    Data DataLoad,
    Link LinkLoad,
    Tag TagLoad,
]

Gives this:

$ roc build --no-link rocLovesZig.roc
thread '<unnamed>' panicked at 'invalid content in tag union variable: (74, Structure(Apply(`6.ItentID(0)`, SubSlice { start: 309, length: 0 })))', crates/compiler/mono/src/layout.rs:2564:23

I don't know if it's known or even what I'm doing wrong but I don't think it's supposed to be doing that...

[ayazhafiz]

Thanks for the report! You're seeing this panic because roc build tries to compile the program even in the presence of type errors, which in this case has hit a code path the compiler didn't expect. If you run roc check first, you'll see some type errors:

── NAMING PROBLEM ────────────────────────────── examples/hello-world/main.roc ─

This annotation does not match the definition immediately following
it:

 9│>  RenderTree : Node -> Str
10│>  RenderTree = \node ->

Is it a typo? If not, put either a newline or comment between them.


── TYPE MISMATCH ─────────────────────────────── examples/hello-world/main.roc ─

Something is off with the body of the main definition:

6│  main : Str
7│  main =  RenderTree Node Data {text: "Ziggy Data!"}
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This RenderTree tag application has the type:

    [RenderTree [Node]a [Data]b { text : Str }]c

But the type annotation on main says it should be:

    Str

────────────────────────────────────────────────────────────────────────────────

The problem here is that Roc doesn't support variable names that are capitalized in their first character - the error message for that should be improved though. Also, Roc types are structural, so RenderTree Node Data {text: "Ziggy Data!"} should instead be renderTree (Data {text: "Ziggy Data!"}). With that your program should compile and execute correctly.

[OBenjaminT]

Ah! I'm not used to that being an important factor, thanks.

I also didn't think it would be type errors because every other time I've run build it has told me about the type errors instead of compiling and crashing.

[ayazhafiz]

yeah, the crash you see here is a compiler bug. Over the long term this should not be happening, and we'll need to fix it, but in the meantime, it is (unfortunately) a somewhat common occurrence.