nim-works/nimskull

Misleading error for case statement when range expression in of-branch is invalid

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#1,511 opened on Apr 11, 2025

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bugcompiler/msgsgood first issue

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Description

Example

type
  E {.pure.} = enum A, B, C, D
  A = int

var e: E
case e
of A..C: discard
of D: discard

Actual Output

test.nim(6, 1) Error: not all cases are covered; missing: {A, B, C}

Expected Output

test.nim(7, 4) Error: type mismatch: got 'typedesc[A]' for 'A' but expected 'E = enum'

Possible Solution

  • This is likely just an error propagation issue for infix, because the real error can be found if --errorMax:0 is used.

Contributor guide

Research direction
Investigate how the Nim compiler handles type checking in case statement of branches, especially when using range expressions. Trace the error message generation to identify where the misleading error about missing cases is produced instead of the type mismatch error.
Tech stack
None
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitNim
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65