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Merged
merged 1 commit into from
Jul 18, 2023
Merged

Improve parameter type inference error messaging #18190

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20 changes: 12 additions & 8 deletions compiler/src/dotty/tools/dotc/reporting/messages.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -160,23 +160,27 @@ extends SyntaxMsg(CaseClassMissingParamListID) {

class AnonymousFunctionMissingParamType(param: untpd.ValDef,
tree: untpd.Function,
pt: Type)
inferredType: Type,
expectedType: Type,
)
(using Context)
extends TypeMsg(AnonymousFunctionMissingParamTypeID) {
def msg(using Context) = {
val ofFun =
if param.name.is(WildcardParamName)
|| (MethodType.syntheticParamNames(tree.args.length + 1) contains param.name)
then i" of expanded function:\n$tree"
then i"\n\nIn expanded function:\n$tree"
else ""

val inferred =
if (pt == WildcardType) ""
else i"\nWhat I could infer was: $pt"
if (inferredType == WildcardType) ""
else i"\n\nPartially inferred type for the parameter: $inferredType"

i"""Missing parameter type
|
|I could not infer the type of the parameter ${param.name}$ofFun.$inferred"""
val expected =
if (expectedType == WildcardType) ""
else i"\n\nExpected type for the whole anonymous function: $expectedType"

i"Could not infer type for parameter ${param.name} of anonymous function$ofFun$inferred$expected"
}

def explain(using Context) = ""
Expand Down Expand Up @@ -2985,4 +2989,4 @@ class ImplausiblePatternWarning(pat: tpd.Tree, selType: Type)(using Context)
i"""|Implausible pattern:
|$pat could match selector of type $selType
|only if there is an `equals` method identifying elements of the two types."""
def explain(using Context) = ""
def explain(using Context) = ""
4 changes: 2 additions & 2 deletions compiler/src/dotty/tools/dotc/typer/Typer.scala
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Expand Up @@ -1620,7 +1620,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
else
inferredFromTarget(param, formal, calleeType, isErased, paramIndex).orElse(
if knownFormal then formal0
else errorType(AnonymousFunctionMissingParamType(param, tree, formal), param.srcPos)
else errorType(AnonymousFunctionMissingParamType(param, tree, inferredType = formal, expectedType = pt), param.srcPos)
)
val paramTpt = untpd.TypedSplice(
(if knownFormal then InferredTypeTree() else untpd.TypeTree())
Expand Down Expand Up @@ -3957,7 +3957,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
sym.isConstructor
|| sym.matchNullaryLoosely
|| Feature.warnOnMigration(msg, tree.srcPos, version = `3.0`)
&& {
&& {
msg.actions
.headOption
.foreach(Rewrites.applyAction)
Expand Down
14 changes: 8 additions & 6 deletions tests/neg/i11350.check
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@@ -1,14 +1,16 @@
-- [E081] Type Error: tests/neg/i11350.scala:1:39 ----------------------------------------------------------------------
1 |class A1[T](action: A1[T] ?=> String = "") // error
| ^
| Missing parameter type
| Could not infer type for parameter evidence$1 of anonymous function
|
| I could not infer the type of the parameter evidence$1.
| What I could infer was: A1[<?>]
| Partially inferred type for the parameter: A1[<?>]
|
| Expected type for the whole anonymous function: (A1[<?>]) ?=> String
-- [E081] Type Error: tests/neg/i11350.scala:2:39 ----------------------------------------------------------------------
2 |class A2[T](action: A1[T] ?=> String = summon[A1[T]]) // error
| ^
| Missing parameter type
| Could not infer type for parameter evidence$2 of anonymous function
|
| Partially inferred type for the parameter: A1[<?>]
|
| I could not infer the type of the parameter evidence$2.
| What I could infer was: A1[<?>]
| Expected type for the whole anonymous function: (A1[<?>]) ?=> String
8 changes: 5 additions & 3 deletions tests/neg/i11561.check
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@@ -1,10 +1,12 @@
-- [E081] Type Error: tests/neg/i11561.scala:2:32 ----------------------------------------------------------------------
2 | val updateText1 = copy(text = _) // error
| ^
| Missing parameter type
| Could not infer type for parameter _$1 of anonymous function
|
| I could not infer the type of the parameter _$1 of expanded function:
| _$1 => State.this.text = _$1.
| In expanded function:
| _$1 => State.this.text = _$1
|
| Expected type for the whole anonymous function: String
-- [E052] Type Error: tests/neg/i11561.scala:3:30 ----------------------------------------------------------------------
3 | val updateText2 = copy(text = (_: String)) // error
| ^^^^^^^^^^^^^^^^^^
Expand Down
16 changes: 10 additions & 6 deletions tests/neg/i17183.check
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@@ -1,14 +1,18 @@
-- [E081] Type Error: tests/neg/i17183.scala:11:24 ---------------------------------------------------------------------
11 |def test = Context(f = (_, _) => ???) // error // error
| ^
| Missing parameter type
| Could not infer type for parameter _$1 of anonymous function
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I wonder if it would be possible to report

 Could not infer type for the 1st parameter of an anonymous function

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I think it would be possible, but I'm not sure it's desirable, I think here we need to show some internals

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The internal names of _ and other unamed variables are only useful to us. Never to the user as they cannot use them in the source.

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@Sporarum Sporarum Jul 13, 2023 •
edited
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I agree, but we need to show the desugarring anyways, as the issue might be that the user missunderstood how _ works
And therefore need names in the desugarring (but these could be something else than _$1)

|
| I could not infer the type of the parameter _$1 of expanded function:
| (_$1, _$2) => ???.
| In expanded function:
| (_$1, _$2) => ???
|
| Expected type for the whole anonymous function: MyFunc
-- [E081] Type Error: tests/neg/i17183.scala:11:27 ---------------------------------------------------------------------
11 |def test = Context(f = (_, _) => ???) // error // error
| ^
| Missing parameter type
| Could not infer type for parameter _$2 of anonymous function
|
| In expanded function:
| (_$1, _$2) => ???
|
| I could not infer the type of the parameter _$2 of expanded function:
| (_$1, _$2) => ???.
| Expected type for the whole anonymous function: MyFunc