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Some usability improvements relating to errors #23370

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Merged
merged 6 commits into from
Jun 17, 2025
Merged

Some usability improvements relating to errors #23370

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5b9f13b
Flag nonsensical capturing types with pure parents as errors
odersky Jun 14, 2025
db11bb7
Don't complain about non-conforming inferred types in empty package
odersky Jun 14, 2025
ef763b9
Refactor checkConformsExpr to allow flexibility in the error reporting
odersky Jun 14, 2025
7a3550f
Better error message if inferred type does not conform to externally …
odersky Jun 14, 2025
b2f30a8
Present aligned dependent functions as generic functions
odersky Jun 15, 2025
523bc78
Print "box" only under -Ycc-verbose
odersky Jun 15, 2025
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Better error message if inferred type does not conform to externally … 
…visible type.
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@odersky
odersky committed Jun 15, 2025
commit 7a3550ff1fae795f7423fd06dd33fdcc578a0e68
12 changes: 11 additions & 1 deletion compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1067,6 +1067,16 @@ class CheckCaptures extends Recheck, SymTransformer:
// too annoying. This is a hole since a defualt getter's result type
// might leak into a type variable.

def fail(tree: Tree, expected: Type, addenda: Addenda): Unit =
def maybeResult = if sym.is(Method) then " result" else ""
report.error(
em"""$sym needs an explicit$maybeResult type because the inferred type does not conform to
|the type that is externally visible in other compilation units.
|
| Inferred type : ${tree.tpe}
| Externally visible type: $expected""",
tree.srcPos)

def addenda(expected: Type) = new Addenda:
override def toAdd(using Context) =
def result = if tree.isInstanceOf[ValDef] then"" else " result"
Expand All @@ -1083,7 +1093,7 @@ class CheckCaptures extends Recheck, SymTransformer:
val expected = tpt.tpe.dropAllRetains
todoAtPostCheck += { () =>
withCapAsRoot:
checkConformsExpr(tp, expected, tree.rhs, addenda(expected))
testAdapted(tp, expected, tree.rhs, addenda(expected))(fail)
// The check that inferred <: expected is done after recheck so that it
// does not interfere with normal rechecking by constraining capture set variables.
}
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72 changes: 24 additions & 48 deletions tests/neg-custom-args/captures/i15116.check
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@@ -1,72 +1,48 @@
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/i15116.scala:5:13 ----------------------------------------
-- Error: tests/neg-custom-args/captures/i15116.scala:5:13 -------------------------------------------------------------
5 | val x = Foo(m) // error
| ^^^^^^
| Found: test.Foo{val m: (Bar.this.m² : test.STR^)}^{Bar.this.m²}
| Required: test.Foo
| value x needs an explicit type because the inferred type does not conform to
| the type that is externally visible in other compilation units.
|
| Inferred type : test.Foo{val m: (Bar.this.m² : test.STR^)}^{Bar.this.m²}
| Externally visible type: test.Foo
|
| where: ^ refers to a fresh root capability in the type of value m²
| m is a value in class Foo
| m² is a value in class Bar
|
|
| Note that the expected type test.Foo
| is the previously inferred type of value x
| which is also the type seen in separately compiled sources.
| The new inferred type test.Foo{val m: (Bar.this.m : test.STR^)}^{Bar.this.m}
| must conform to this type.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/i15116.scala:7:13 ----------------------------------------
-- Error: tests/neg-custom-args/captures/i15116.scala:7:13 -------------------------------------------------------------
7 | val x = Foo(m) // error
| ^^^^^^
| Found: test.Foo{val m: (Baz.this.m² : test.STR^)}^{Baz.this.m²}
| Required: test.Foo
| value x needs an explicit type because the inferred type does not conform to
| the type that is externally visible in other compilation units.
|
| Inferred type : test.Foo{val m: (Baz.this.m² : test.STR^)}^{Baz.this.m²}
| Externally visible type: test.Foo
|
| where: ^ refers to a fresh root capability in the type of value m²
| m is a value in class Foo
| m² is a value in trait Baz
|
|
| Note that the expected type test.Foo
| is the previously inferred type of value x
| which is also the type seen in separately compiled sources.
| The new inferred type test.Foo{val m: (Baz.this.m : test.STR^)}^{Baz.this.m}
| must conform to this type.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/i15116.scala:9:13 ----------------------------------------
-- Error: tests/neg-custom-args/captures/i15116.scala:9:13 -------------------------------------------------------------
9 | val x = Foo(m) // error
| ^^^^^^
| Found: test.Foo{val m: (Bar1.this.m² : test.STR^)}^{Bar1.this.m²}
| Required: test.Foo
| value x needs an explicit type because the inferred type does not conform to
| the type that is externally visible in other compilation units.
|
| Inferred type : test.Foo{val m: (Bar1.this.m² : test.STR^)}^{Bar1.this.m²}
| Externally visible type: test.Foo
|
| where: ^ refers to a fresh root capability in the type of value m²
| m is a value in class Foo
| m² is a value in class Bar1
|
|
| Note that the expected type test.Foo
| is the previously inferred type of value x
| which is also the type seen in separately compiled sources.
| The new inferred type test.Foo{val m: (Bar1.this.m : test.STR^)}^{Bar1.this.m}
| must conform to this type.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/i15116.scala:11:13 ---------------------------------------
-- Error: tests/neg-custom-args/captures/i15116.scala:11:13 ------------------------------------------------------------
11 | val x = Foo(m) // error
| ^^^^^^
| Found: test.Foo{val m: (Baz2.this.m² : test.STR^)}^{Baz2.this.m²}
| Required: test.Foo
| value x needs an explicit type because the inferred type does not conform to
| the type that is externally visible in other compilation units.
|
| Inferred type : test.Foo{val m: (Baz2.this.m² : test.STR^)}^{Baz2.this.m²}
| Externally visible type: test.Foo
|
| where: ^ refers to a fresh root capability in the type of value m²
| m is a value in class Foo
| m² is a value in trait Baz2
|
|
| Note that the expected type test.Foo
| is the previously inferred type of value x
| which is also the type seen in separately compiled sources.
| The new inferred type test.Foo{val m: (Baz2.this.m : test.STR^)}^{Baz2.this.m}
| must conform to this type.
|
| longer explanation available when compiling with `-explain`