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Improve error message about missing type of context function parameter (
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#18788)

Also, change formatting of msg closer to what it was before. I find that
more legible.
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@odersky
odersky authored Oct 30, 2023
2 parents 5288dff + 1a16654 commit 6792b64
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Showing 6 changed files with 58 additions and 32 deletions.
21 changes: 12 additions & 9 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 @@ -7,7 +7,7 @@ import Contexts._
import Decorators._, Symbols._, Names._, NameOps._, Types._, Flags._, Phases._
import Denotations.SingleDenotation
import SymDenotations.SymDenotation
import NameKinds.WildcardParamName
import NameKinds.{WildcardParamName, ContextFunctionParamName}
import parsing.Scanners.Token
import parsing.Tokens
import printing.Highlighting._
Expand Down Expand Up @@ -167,21 +167,24 @@ class AnonymousFunctionMissingParamType(param: untpd.ValDef,
(using Context)
extends TypeMsg(AnonymousFunctionMissingParamTypeID) {
def msg(using Context) = {
val ofFun =
val paramDescription =
if param.name.is(WildcardParamName)
|| (MethodType.syntheticParamNames(tree.args.length + 1) contains param.name)
then i"\n\nIn expanded function:\n$tree"
|| param.name.is(ContextFunctionParamName)
|| MethodType.syntheticParamNames(tree.args.length + 1).contains(param.name)
then i"\nin expanded function:\n $tree"
else ""

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

val expected =
if (expectedType == WildcardType) ""
else i"\n\nExpected type for the whole anonymous function: $expectedType"
if expectedType == WildcardType then ""
else i"\nExpected type for the whole anonymous function:\n $expectedType"

i"Could not infer type for parameter ${param.name} of anonymous function$ofFun$inferred$expected"
i"""Missing parameter type
|
|I could not infer the type of the parameter ${param.name}$paramDescription$inferred$expected"""
}

def explain(using Context) = ""
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22 changes: 14 additions & 8 deletions tests/neg/i11350.check
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Original file line number Diff line number Diff line change
@@ -1,16 +1,22 @@
-- [E081] Type Error: tests/neg/i11350.scala:1:39 ----------------------------------------------------------------------
1 |class A1[T](action: A1[T] ?=> String = "") // error
| ^
| Could not infer type for parameter contextual$1 of anonymous function
| Missing parameter type
|
| Partially inferred type for the parameter: A1[<?>]
|
| Expected type for the whole anonymous function: (A1[<?>]) ?=> String
| I could not infer the type of the parameter contextual$1
| in expanded function:
| contextual$1 ?=> ""
| What I could infer was: 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
| ^
| Could not infer type for parameter contextual$2 of anonymous function
|
| Partially inferred type for the parameter: A1[<?>]
| Missing parameter type
|
| Expected type for the whole anonymous function: (A1[<?>]) ?=> String
| I could not infer the type of the parameter contextual$2
| in expanded function:
| contextual$2 ?=> summon[A1[T]]
| What I could infer was: A1[<?>]
| Expected type for the whole anonymous function:
| (A1[<?>]) ?=> String
11 changes: 6 additions & 5 deletions tests/neg/i11561.check
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Original file line number Diff line number Diff line change
@@ -1,12 +1,13 @@
-- [E081] Type Error: tests/neg/i11561.scala:2:32 ----------------------------------------------------------------------
2 | val updateText1 = copy(text = _) // error
| ^
| Could not infer type for parameter _$1 of anonymous function
| Missing parameter type
|
| In expanded function:
| _$1 => State.this.text = _$1
|
| Expected type for the whole anonymous function: String
| I could not infer the type of the parameter _$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
| ^^^^^^^^^^^^^^^^^^
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22 changes: 12 additions & 10 deletions tests/neg/i17183.check
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@@ -1,18 +1,20 @@
-- [E081] Type Error: tests/neg/i17183.scala:11:24 ---------------------------------------------------------------------
11 |def test = Context(f = (_, _) => ???) // error // error
| ^
| Could not infer type for parameter _$1 of anonymous function
| Missing parameter type
|
| In expanded function:
| (_$1, _$2) => ???
|
| Expected type for the whole anonymous function: MyFunc
| I could not infer the type of the parameter _$1
| 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
| ^
| Could not infer type for parameter _$2 of anonymous function
|
| In expanded function:
| (_$1, _$2) => ???
| Missing parameter type
|
| Expected type for the whole anonymous function: MyFunc
| I could not infer the type of the parameter _$2
| in expanded function:
| (_$1, _$2) => ???
| Expected type for the whole anonymous function:
| MyFunc
11 changes: 11 additions & 0 deletions tests/neg/i18188.check
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
-- [E081] Type Error: tests/neg/i18188.scala:3:39 ----------------------------------------------------------------------
3 |class A1[T](action: A1[T] ?=> String = "") // error
| ^
| Missing parameter type
|
| I could not infer the type of the parameter contextual$1
| in expanded function:
| contextual$1 ?=> ""
| What I could infer was: dotty.tools.dotc.typer.A1[<?>]
| Expected type for the whole anonymous function:
| (dotty.tools.dotc.typer.A1[<?>]) ?=> String
3 changes: 3 additions & 0 deletions tests/neg/i18188.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
package dotty.tools.dotc.typer

class A1[T](action: A1[T] ?=> String = "") // error

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