Comments (1)
jiribenes
commented on August 21, 2024
I have a very simple fix for this that reports something like the following by constructing a string
Non exhaustive pattern matching, missing case Fork(Fork(_, false, _), _, _)
Non exhaustive pattern matching, missing case Fork(Fork(_, _, Fork(_, _, _)), _, _))
Non exhaustive pattern matching, missing case Fork(Leaf(), _, _)
for the following code:
type BooleyTree {
Leaf()
Fork(l: BooleyTree, v: Bool, r: BooleyTree)
}
def testTree(t: BooleyTree): Int = t match {
case Leaf() => 42
case Fork(Fork(l, true, Leaf()), _, r) => <>
}However, I'm not 100% convinced that creating a string is the best solution here. If we instead construct the actual term, then we could later on use LSP to automatically suggest a fix (just insert a pp"case $MyPrettyTerm => <>").
In case I forget, here's the (very rough!) patch:
Warning: This patch is quite limited, has a lot of code duplication and doesn't actually consider two out of the four cases at all.
diff --git i/effekt/shared/src/main/scala/effekt/typer/ExhaustivityChecker.scala w/effekt/shared/src/main/scala/effekt/typer/ExhaustivityChecker.scala
index a9e18e68..33185921 100644
--- i/effekt/shared/src/main/scala/effekt/typer/ExhaustivityChecker.scala
+++ w/effekt/shared/src/main/scala/effekt/typer/ExhaustivityChecker.scala
@@ -150,13 +150,35 @@ object ExhaustivityChecker {
// ---------------
def reportNonExhaustive()(using C: ErrorReporter): Unit = missingCases.foreach {
case Missing.Tag(ctor, at) =>
- C.error(pp"Non exhaustive pattern matching, missing case for ${ ctor }")
+ // TODO: wouldn't it be better to construct terms and then pretty print those?
+ def pretty(ctor: Constructor, at: Trace, soFar: String): String = at match {
+ case Trace.Root(_) => soFar
+ case Trace.Child(childCtor, field, outer) => childCtor.fields match
+ case Nil => C.panic("reportNonExhaustive: impossible, child trace has no fields")
+ case _ =>
+ val acc = s"${childCtor.name}(${childCtor.fields.map { f => if f == field then soFar else "_" }.mkString(", ")})"
+ pretty(childCtor, outer, acc)
+ }
+ val root = ctor.fields match
+ case Nil => s"${ctor.name}()"
+ case _ => s"${ctor.name}(${ctor.fields.map { _f => "_" }.mkString(", ")})"
+ C.error(pp"Non exhaustive pattern matching, missing case ${pretty(ctor, at, root)}")
case Missing.Guard(term) =>
C.at(term) {
C.error(pp"Non exhaustive pattern matching, guard could be false which is not covered")
}
case Missing.Literal(value, tpe, at) =>
- C.error(pp"Non exhaustive pattern matching, missing case for ${value}")
+ // TODO: wouldn't it be better to construct terms and then pretty print those?
+ def pretty(value: Any, at: Trace, soFar: String): String = at match {
+ case Trace.Root(_) => soFar
+ case Trace.Child(childCtor, field, outer) => childCtor.fields match
+ case Nil => C.panic("reportNonExhaustive: impossible, child trace has no fields")
+ case _ =>
+ val acc = s"${childCtor.name}(${childCtor.fields.map { f => if f == field then soFar else "_" }.mkString(", ")})"
+ pretty(value, outer, acc)
+ }
+ val root = pp"${value}"
+ C.error(pp"Non exhaustive pattern matching, missing case ${pretty(value, at, root)}")
case Missing.Default(tpe, at) =>
C.error(pp"Non exhaustive pattern matching, scrutinees of type ${tpe} require a default case")
}EDIT: for completeness, here's what the code above outputs for the original problem:
Non exhaustive pattern matching, missing case Cons(_, Cons(_, _))
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Related Issues (20)
- References escape their region when using `var` HOT 1
- More descriptive comments when generating LLVM from Machine
- Unexpected end of input on opening brace after newline HOT 1
- Existentially quantified types are defined in outer scope HOT 2
- Investigate using memory use markers in the generated LLVM
- Renamer stack-overflows on large test suites HOT 1
- Unicode escapes outside literals
- Improve lexer resilience
- LSP inlay hints HOT 1
- Nested comments are not lexed correctly
- Non-unique identifiers when prettyprinting lifted IR
- Move to a rolling release scheme
- Use CLI subcommands HOT 1
- Variable with boxed function allows call of function without necessary captures in scope
- Add `--version` CLI flag
- Add a getter for environment variables to stdlib
- Unicode escapes in the MLton backend
- Compiler crash on leftover `do`-call in FFI after capability passing HOT 4
- Recursive state cannot be annotated HOT 2
- Capability escapes from higher-order function HOT 4
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