Reproductions of poor error messages

[ayazhafiz]

We have some projects around improving the quality of error messages in type mismatches:

• https://roc.zulipchat.com/#narrow/stream/231635-compiler-development/topic/aliases.20in.20error.20messages.20exposing.20internals
• Poor error message when when condition type doesn't match branch patterns #4007
• Improve quality of non-local type error messages #3692

This issue is a bulletin board to collect reproductions of poor error messages so that we have test cases for improvements!

When listing a reproduction, please title your comment with # Reproduction (so that it stands out) and please provide a minimal reproduction of the test case! If your reproduction comes from another issue, you can instead link to that issue.

Examples:

Reproduction comment

Reproduction

Code:

» X : [A Str, B Str]
…
… x : Result X []
… x =
…   if True then Ok (A "") else Ok (B "")
…
… when x is
…   Ok A -> ""
…   Ok B -> ""

Error message:

── TYPE MISMATCH ───────────────────────────────────────────────────────────────

The branches of this when expression don't match the condition:

10│>      when x is
11│         Ok A -> ""
12│         Ok B -> ""

This x value is a:

    Result X []

But the branch patterns have type:

    [Ok [A, B]]

The branches must be cases of the when condition's type!

Reproduction comment linking to issue

Reproduction

#4007

[ghigt]

Reproduction

Code:

app "main"
    packages { pf: "./roc/examples/cli/cli-platform/main.roc" }
    imports [pf.Program, pf.Stdout, pf.Task]
    provides [main] to pf

main =
    Task.attempt processTask \p ->
        when p is
            Ok s -> Stdout.line s
            Err ReadErr -> Stdout.line "Tried to read"
            # Err WriteErr -> Stdout.line "Tried to write"

    |> Program.quick

processTask : Task.Task Str [ReadErr, WriteErr] []*

Error message:

── TYPE MISMATCH ──────────────────────────────────────────────────── test.roc ─

This 2nd argument to attempt has an unexpected type:

 7│>      Task.attempt processTask \p ->
 8│>          when p is
 9│>              Ok s -> Stdout.line s
10│>              Err ReadErr -> Stdout.line "Tried to read"

The argument is an anonymous function of type:

    [Err [ReadErr], Ok Str] -> Task {} * [Write [Stdout]*]* ?

But attempt needs its 2nd argument to be:

    Result Str [ReadErr, WriteErr] -> Task {} * [Write [Stdout]*]* ?

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

[cjduncana]

Reproduction

#4274
#4311

[brian-carroll]

#4370

[benzen]

Reproduction

app "hello-world"
    packages { pf: "https://github.com/roc-lang/basic-cli/releases/download/0.7.1/Icc3xJoIixF3hCcfXrDwLCu4wQHtNdPyoJkEbkgIElA.tar.br" }
    imports [pf.Stdout]
    provides [main] to pf

filterNumbers = \ line ->
  line
  |> Str.graphemes
  |> List.keepIf \ graphem -> List.contains numbers, graphem

main = Stdout.line "hello"

thread 'main' panicked at 'not yet implemented: unhandled parse error: Pattern(IndentEnd(@523), @515)', crates/reporting/src/error/parse.rs:690:14
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

And the compiler hang also

[benzen]

Reproduction

filterNumbers = \ line ->
  line
  |> Str.graphemes
  |> List.keepIf List.contains numbers, g
  |> Str.joinWith "\n"
  

── UNRECOGNIZED NAME ──────────────────────────────────────────────── main.roc ─

Nothing is named `g` in this scope.

23│    |> List.keepIf (\ g -> List.contains numbers, g)
                                                     ^

Did you mean one of these?

    U8
    Eq
    I8
    Ok

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

[nightingale-m]

Reproduction

Code:

collatzStep = \number, stepCount ->
    if number == 1 then
        (number, stepCount)
    # else
    if Num.isEven number then
        collatzStep (number // 2) (stepCount + 1)
    else
        collatzStep (number * 3 + 1) (stepCount + 1)

Error message:

── STATEMENT AFTER EXPRESSION in CollatzConjecture.roc ─────────────────────────

I just finished parsing an expression with a series of definitions,

and this line is indented as if it's intended to be part of that
expression:


         ^

However, I already saw the final expression in that series of
definitions.