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OlivierBlanvillainOlivierBlanvillain
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Fix #10747: Raise type error on unreducible MT
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6 files changed

+63
-94
lines changed

6 files changed

+63
-94
lines changed

‎compiler/src/dotty/tools/dotc/core/MatchTypeTrace.scala

Lines changed: 17 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -102,12 +102,22 @@ object MatchTypeTrace:
102102
i""" failed since selector $scrut
103103
| is uninhabited (there are no values of that type)."""
104104
case Stuck(scrut, stuckCase, otherCases) =>
105-
i""" failed since selector $scrut
106-
| does not match ${caseText(stuckCase)}
107-
| and cannot be shown to be disjoint from it either.
108-
| Therefore, reduction cannot advance to the remaining case${if otherCases.length == 1 then "" else "s"}
109-
|
110-
| ${casesText(otherCases)}"""
105+
val msg =
106+
i""" failed since selector $scrut
107+
| does not match ${caseText(stuckCase)}
108+
| and cannot be shown to be disjoint from it either."""
109+
if otherCases.length == 0 then msg
110+
else
111+
val s = if otherCases.length == 1 then "" else "s"
112+
i"""$msg
113+
| Therefore, reduction cannot advance to the remaining case$s
114+
|
115+
| ${casesText(otherCases)}"""
111116

112-
end MatchTypeTrace
117+
def noMatchesText(scrut: Type, cases: List[Type])(using Context): String =
118+
i"""failed since selector $scrut
119+
|matches none of the cases
120+
|
121+
| ${casesText(cases)}"""
113122

123+
end MatchTypeTrace

‎compiler/src/dotty/tools/dotc/core/TypeComparer.scala

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -2924,14 +2924,13 @@ class TrackingTypeComparer(initctx: Context) extends TypeComparer(initctx) {
29242924
case None =>
29252925
recur(remaining1)
29262926
case Some(NoType) =>
2927-
if remaining1.isEmpty then MatchTypeTrace.noMatches(scrut, cases)
2928-
else MatchTypeTrace.stuck(scrut, cas, remaining1)
2927+
MatchTypeTrace.stuck(scrut, cas, remaining1)
29292928
NoType
29302929
case Some(tp) =>
29312930
tp
29322931
case Nil =>
2933-
MatchTypeTrace.noMatches(scrut, cases)
2934-
NoType
2932+
val casesText = MatchTypeTrace.noMatchesText(scrut, cases)
2933+
throw new TypeError(s"Match type reduction $casesText")
29352934

29362935
inFrozenConstraint {
29372936
// Empty types break the basic assumption that if a scrutinee and a

‎tests/neg/10747.scala

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
type Foo[A] = A match {
2+
case Int => String
3+
}
4+
5+
type B = Foo[Boolean] // error

‎tests/neg/6697.check

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,8 +7,7 @@
77
|
88
| trying to reduce Test.Sub[O]
99
| failed since selector O
10-
| matches none of the cases
11-
|
12-
| case Test.Of[sup, sub] => sub
10+
| does not match case Test.Of[sup, sub] => sub
11+
| and cannot be shown to be disjoint from it either.
1312

1413
longer explanation available when compiling with `-explain`

‎tests/neg/i12049.check

Lines changed: 24 additions & 52 deletions
Original file line numberDiff line numberDiff line change
@@ -15,39 +15,22 @@
1515
| case B => String
1616

1717
longer explanation available when compiling with `-explain`
18-
-- [E007] Type Mismatch Error: tests/neg/i12049.scala:14:17 ------------------------------------------------------------
18+
-- Error: tests/neg/i12049.scala:14:23 ---------------------------------------------------------------------------------
1919
14 |val y3: String = ??? : Last[Int *: Int *: Boolean *: String *: EmptyTuple] // error
20-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
21-
| Found: Last[EmptyTuple.type]
22-
| Required: String
20+
| ^
21+
| Match type reduction failed since selector EmptyTuple.type
22+
| matches none of the cases
2323
|
24-
| Note: a match type could not be fully reduced:
25-
|
26-
| trying to reduce Last[EmptyTuple.type]
27-
| failed since selector EmptyTuple.type
28-
| matches none of the cases
29-
|
30-
| case _ *: _ *: t => Last[t]
31-
| case t *: EmptyTuple => t
32-
33-
longer explanation available when compiling with `-explain`
34-
-- [E007] Type Mismatch Error: tests/neg/i12049.scala:22:20 ------------------------------------------------------------
24+
| case _ *: _ *: t => Last[t]
25+
| case t *: EmptyTuple => t
26+
-- Error: tests/neg/i12049.scala:22:26 ---------------------------------------------------------------------------------
3527
22 |val z3: (A, B, A) = ??? : Reverse[(A, B, A)] // error
36-
| ^^^^^^^^^^^^^^^^^^^^^^^^
37-
| Found: Tuple.Concat[Reverse[A *: EmptyTuple.type], (B, A)]
38-
| Required: (A, B, A)
39-
|
40-
| Note: a match type could not be fully reduced:
41-
|
42-
| trying to reduce Tuple.Concat[Reverse[A *: EmptyTuple.type], (B, A)]
43-
| trying to reduce Reverse[A *: EmptyTuple.type]
44-
| failed since selector A *: EmptyTuple.type
45-
| matches none of the cases
28+
| ^
29+
| Match type reduction failed since selector A *: EmptyTuple.type
30+
| matches none of the cases
4631
|
47-
| case t1 *: t2 *: ts => Tuple.Concat[Reverse[ts], (t2, t1)]
48-
| case EmptyTuple => EmptyTuple
49-
50-
longer explanation available when compiling with `-explain`
32+
| case t1 *: t2 *: ts => Tuple.Concat[Reverse[ts], (t2, t1)]
33+
| case EmptyTuple => EmptyTuple
5134
-- Error: tests/neg/i12049.scala:24:20 ---------------------------------------------------------------------------------
5235
24 |val _ = summon[M[B]] // error
5336
| ^
@@ -62,33 +45,22 @@ longer explanation available when compiling with `-explain`
6245
| Therefore, reduction cannot advance to the remaining case
6346
|
6447
| case B => String
65-
-- Error: tests/neg/i12049.scala:25:78 ---------------------------------------------------------------------------------
48+
-- Error: tests/neg/i12049.scala:25:26 ---------------------------------------------------------------------------------
6649
25 |val _ = summon[String =:= Last[Int *: Int *: Boolean *: String *: EmptyTuple]] // error
67-
| ^
68-
| Cannot prove that String =:= Last[EmptyTuple.type].
69-
|
70-
| Note: a match type could not be fully reduced:
50+
| ^
51+
| Match type reduction failed since selector EmptyTuple.type
52+
| matches none of the cases
7153
|
72-
| trying to reduce Last[EmptyTuple.type]
73-
| failed since selector EmptyTuple.type
74-
| matches none of the cases
75-
|
76-
| case _ *: _ *: t => Last[t]
77-
| case t *: EmptyTuple => t
78-
-- Error: tests/neg/i12049.scala:26:48 ---------------------------------------------------------------------------------
54+
| case _ *: _ *: t => Last[t]
55+
| case t *: EmptyTuple => t
56+
-- Error: tests/neg/i12049.scala:26:29 ---------------------------------------------------------------------------------
7957
26 |val _ = summon[(A, B, A) =:= Reverse[(A, B, A)]] // error
80-
| ^
81-
| Cannot prove that (A, B, A) =:= Tuple.Concat[Reverse[A *: EmptyTuple.type], (B, A)].
82-
|
83-
| Note: a match type could not be fully reduced:
84-
|
85-
| trying to reduce Tuple.Concat[Reverse[A *: EmptyTuple.type], (B, A)]
86-
| trying to reduce Reverse[A *: EmptyTuple.type]
87-
| failed since selector A *: EmptyTuple.type
88-
| matches none of the cases
58+
| ^
59+
| Match type reduction failed since selector A *: EmptyTuple.type
60+
| matches none of the cases
8961
|
90-
| case t1 *: t2 *: ts => Tuple.Concat[Reverse[ts], (t2, t1)]
91-
| case EmptyTuple => EmptyTuple
62+
| case t1 *: t2 *: ts => Tuple.Concat[Reverse[ts], (t2, t1)]
63+
| case EmptyTuple => EmptyTuple
9264
-- [E008] Not Found Error: tests/neg/i12049.scala:28:21 ----------------------------------------------------------------
9365
28 |val _ = (??? : M[B]).length // error
9466
| ^^^^^^^^^^^^^^^^^^^

‎tests/neg/matchtype-seq.check

Lines changed: 12 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -1,35 +1,19 @@
1-
-- [E007] Type Mismatch Error: tests/neg/matchtype-seq.scala:9:18 ------------------------------------------------------
1+
-- Error: tests/neg/matchtype-seq.scala:9:11 ---------------------------------------------------------------------------
22
9 | identity[T1[3]]("") // error
3-
| ^^
4-
| Found: ("" : String)
5-
| Required: Test.T1[(3 : Int)]
3+
| ^
4+
| Match type reduction failed since selector (3 : Int)
5+
| matches none of the cases
66
|
7-
| Note: a match type could not be fully reduced:
8-
|
9-
| trying to reduce Test.T1[(3 : Int)]
10-
| failed since selector (3 : Int)
11-
| matches none of the cases
12-
|
13-
| case (1 : Int) => Int
14-
| case (2 : Int) => String
15-
16-
longer explanation available when compiling with `-explain`
17-
-- [E007] Type Mismatch Error: tests/neg/matchtype-seq.scala:10:18 -----------------------------------------------------
7+
| case (1 : Int) => Int
8+
| case (2 : Int) => String
9+
-- Error: tests/neg/matchtype-seq.scala:10:11 --------------------------------------------------------------------------
1810
10 | identity[T1[3]](1) // error
19-
| ^
20-
| Found: (1 : Int)
21-
| Required: Test.T1[(3 : Int)]
11+
| ^
12+
| Match type reduction failed since selector (3 : Int)
13+
| matches none of the cases
2214
|
23-
| Note: a match type could not be fully reduced:
24-
|
25-
| trying to reduce Test.T1[(3 : Int)]
26-
| failed since selector (3 : Int)
27-
| matches none of the cases
28-
|
29-
| case (1 : Int) => Int
30-
| case (2 : Int) => String
31-
32-
longer explanation available when compiling with `-explain`
15+
| case (1 : Int) => Int
16+
| case (2 : Int) => String
3317
-- [E007] Type Mismatch Error: tests/neg/matchtype-seq.scala:11:20 -----------------------------------------------------
3418
11 | identity[T1[Int]]("") // error
3519
| ^^

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