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dwijnanddwijnand
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Fix warning message for matching on redundant nulls (#21850)
2 parents 8ab7ebe + 1b48966 commit fa43ab8

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11 files changed

+145
-24
lines changed

11 files changed

+145
-24
lines changed

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

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -337,7 +337,7 @@ abstract class SymbolLoader extends LazyType { self =>
337337
val sym = root.symbol
338338
def associatedFile = root.symbol.associatedFile match
339339
case file: AbstractFile => file
340-
case _ => NoAbstractFile
340+
case null => NoAbstractFile
341341
ctx.profiler.onCompletion(sym, associatedFile)(body)
342342
}
343343

‎compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

Lines changed: 22 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -116,6 +116,7 @@ object SpaceEngine {
116116
def isSubspace(a: Space, b: Space)(using Context): Boolean = a.isSubspace(b)
117117
def canDecompose(typ: Typ)(using Context): Boolean = typ.canDecompose
118118
def decompose(typ: Typ)(using Context): List[Typ] = typ.decompose
119+
def nullSpace(using Context): Space = Typ(ConstantType(Constant(null)), decomposed = false)
119120

120121
/** Simplify space such that a space equal to `Empty` becomes `Empty` */
121122
def computeSimplify(space: Space)(using Context): Space = trace(i"simplify($space)")(space match {
@@ -336,6 +337,13 @@ object SpaceEngine {
336337
case pat: Ident if isBackquoted(pat) =>
337338
Typ(pat.tpe, decomposed = false)
338339

340+
case Ident(nme.WILDCARD) =>
341+
val tp = pat.tpe.stripAnnots.widenSkolem
342+
val isNullable = tp.isInstanceOf[FlexibleType] || tp.classSymbol.isNullableClass
343+
val tpSpace = Typ(erase(tp, isValue = true), decomposed = false)
344+
if isNullable then Or(tpSpace :: nullSpace :: Nil)
345+
else tpSpace
346+
339347
case Ident(_) | Select(_, _) =>
340348
Typ(erase(pat.tpe.stripAnnots.widenSkolem, isValue = true), decomposed = false)
341349

@@ -667,7 +675,7 @@ object SpaceEngine {
667675
case tp => (tp, Nil)
668676
val (tp, typeArgs) = getAppliedClass(tpOriginal)
669677
// This function is needed to get the arguments of the types that will be applied to the class.
670-
// This is necessary because if the arguments of the types contain Nothing,
678+
// This is necessary because if the arguments of the types contain Nothing,
671679
// then this can affect whether the class will be taken into account during the exhaustiveness check
672680
def getTypeArgs(parent: Symbol, child: Symbol, typeArgs: List[Type]): List[Type] =
673681
val superType = child.typeRef.superType
@@ -930,7 +938,7 @@ object SpaceEngine {
930938
if isNullable && !ctx.mode.is(Mode.SafeNulls)
931939
then project(OrType(selTyp, ConstantType(Constant(null)), soft = false))
932940
else project(selTyp)
933-
941+
var hadNullOnly = false
934942
@tailrec def recur(cases: List[CaseDef], prevs: List[Space], deferred: List[Tree]): Unit =
935943
cases match
936944
case Nil =>
@@ -946,11 +954,19 @@ object SpaceEngine {
946954

947955
if pat != EmptyTree // rethrow case of catch uses EmptyTree
948956
&& !pat.symbol.isAllOf(SyntheticCase, butNot=Method) // ExpandSAMs default cases use SyntheticCase
949-
&& isSubspace(covered, prev)
950957
then
951-
val nullOnly = isNullable && rest.isEmpty && isWildcardArg(pat)
952-
val msg = if nullOnly then MatchCaseOnlyNullWarning() else MatchCaseUnreachable()
953-
report.warning(msg, pat.srcPos)
958+
if isSubspace(covered, prev) then
959+
report.warning(MatchCaseUnreachable(), pat.srcPos)
960+
else if isNullable && !hadNullOnly && isWildcardArg(pat)
961+
&& isSubspace(covered, Or(prev :: nullSpace :: Nil)) then
962+
// Issue OnlyNull warning only if:
963+
// 1. The target space is nullable;
964+
// 2. OnlyNull warning has not been issued before;
965+
// 3. The pattern is a wildcard pattern;
966+
// 4. The pattern is not covered by the previous cases,
967+
// but covered by the previous cases with null.
968+
hadNullOnly = true
969+
report.warning(MatchCaseOnlyNullWarning(), pat.srcPos)
954970

955971
// in redundancy check, take guard as false in order to soundly approximate
956972
val newPrev = if guard.isEmpty then covered :: prevs else prevs

‎tests/explicit-nulls/warn/i21577.check

Lines changed: 9 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,25 +1,29 @@
11
-- [E121] Pattern Match Warning: tests/explicit-nulls/warn/i21577.scala:5:9 --------------------------------------------
2-
5 | case _ => // warn
2+
5 | case _ => // warn: null only
33
| ^
44
| Unreachable case except for null (if this is intentional, consider writing case null => instead).
55
-- [E121] Pattern Match Warning: tests/explicit-nulls/warn/i21577.scala:12:9 -------------------------------------------
6-
12 | case _ => // warn
6+
12 | case _ => // warn: null only
77
| ^
88
| Unreachable case except for null (if this is intentional, consider writing case null => instead).
9+
-- [E121] Pattern Match Warning: tests/explicit-nulls/warn/i21577.scala:16:7 -------------------------------------------
10+
16 | case _ => // warn: null only
11+
| ^
12+
| Unreachable case except for null (if this is intentional, consider writing case null => instead).
913
-- [E030] Match case Unreachable Warning: tests/explicit-nulls/warn/i21577.scala:20:7 ----------------------------------
10-
20 | case _ => // warn
14+
20 | case _ => // warn: unreachable
1115
| ^
1216
| Unreachable case
1317
-- [E029] Pattern Match Exhaustivity Warning: tests/explicit-nulls/warn/i21577.scala:29:27 -----------------------------
14-
29 |def f7(s: String | Null) = s match // warn
18+
29 |def f7(s: String | Null) = s match // warn: not exhuastive
1519
| ^
1620
| match may not be exhaustive.
1721
|
1822
| It would fail on pattern case: _: Null
1923
|
2024
| longer explanation available when compiling with `-explain`
2125
-- [E029] Pattern Match Exhaustivity Warning: tests/explicit-nulls/warn/i21577.scala:36:33 -----------------------------
22-
36 |def f9(s: String | Int | Null) = s match // warn
26+
36 |def f9(s: String | Int | Null) = s match // warn: not exhuastive
2327
| ^
2428
| match may not be exhaustive.
2529
|

‎tests/explicit-nulls/warn/i21577.scala

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -2,22 +2,22 @@ def f(s: String) =
22
val s2 = s.trim()
33
s2 match
44
case s3: String =>
5-
case _ => // warn
5+
case _ => // warn: null only
66

77

88
def f2(s: String | Null) =
99
val s2 = s.nn.trim()
1010
s2 match
1111
case s3: String =>
12-
case _ => // warn
12+
case _ => // warn: null only
1313

1414
def f3(s: String | Null) = s match
1515
case s2: String =>
16-
case _ =>
16+
case _ => // warn: null only
1717

1818
def f5(s: String) = s match
1919
case _: String =>
20-
case _ => // warn
20+
case _ => // warn: unreachable
2121

2222
def f6(s: String) = s.trim() match
2323
case _: String =>
@@ -26,13 +26,13 @@ def f6(s: String) = s.trim() match
2626
def f61(s: String) = s.trim() match
2727
case _: String =>
2828

29-
def f7(s: String | Null) = s match // warn
29+
def f7(s: String | Null) = s match // warn: not exhuastive
3030
case _: String =>
3131

3232
def f8(s: String | Null) = s match
3333
case _: String =>
3434
case null =>
3535

36-
def f9(s: String | Int | Null) = s match // warn
36+
def f9(s: String | Int | Null) = s match // warn: not exhuastive
3737
case _: String =>
3838
case null =>

‎tests/patmat/i12530.check

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,2 +1 @@
11
6: Match case Unreachable
2-
14: Match case Unreachable

‎tests/patmat/null.check

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,4 @@
1-
6: Pattern Match
1+
6: Match case Unreachable
22
13: Pattern Match
3+
18: Match case Unreachable
34
20: Pattern Match

‎tests/warn/i20121.scala

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -5,8 +5,8 @@ case class CC_B[A](a: A) extends T_A[A, X]
55

66
val v_a: T_A[X, X] = CC_B(null)
77
val v_b = v_a match
8-
case CC_B(_) => 0 // warn: unreachable
9-
case _ => 1
8+
case CC_B(_) => 0
9+
case _ => 1 // warn: null only
1010
// for CC_B[A] to match T_A[X, X]
1111
// A := X
1212
// so require X, aka T_A[Byte, Byte]

‎tests/warn/i20122.scala

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@ case class CC_E(a: CC_C[Char, Byte])
77

88
val v_a: T_B[Int, CC_A] = CC_B(CC_E(CC_C(null)))
99
val v_b = v_a match
10-
case CC_B(CC_E(CC_C(_))) => 0 // warn: unreachable
10+
case CC_B(CC_E(CC_C(_))) => 0
1111
case _ => 1
1212
// for CC_B[A, C] to match T_B[C, CC_A]
1313
// C <: Int, ok

‎tests/warn/i20123.scala

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ case class CC_G[A, C](c: C) extends T_A[A, C]
88
val v_a: T_A[Boolean, T_B[Boolean]] = CC_G(null)
99
val v_b = v_a match {
1010
case CC_D() => 0
11-
case CC_G(_) => 1 // warn: unreachable
11+
case CC_G(_) => 1
1212
// for CC_G[A, C] to match T_A[Boolean, T_B[Boolean]]
1313
// A := Boolean, which is ok
1414
// C := T_B[Boolean],

‎tests/warn/redundant-null.check

Lines changed: 56 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,56 @@
1+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:10:7 -----------------------------------------
2+
10 | case _: n.type => // warn: unreachable
3+
| ^^^^^^^^^
4+
| Unreachable case
5+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:12:7 -----------------------------------------
6+
12 | case _ => // warn: unreachable
7+
| ^
8+
| Unreachable case
9+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:13:7 -----------------------------------------
10+
13 | case _ => // warn: unreachable
11+
| ^
12+
| Unreachable case
13+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:18:7 -----------------------------------------
14+
18 | case _ => 3 // warn: unreachable
15+
| ^
16+
| Unreachable case
17+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:23:7 -----------------------------------------
18+
23 | case _: B => // warn: unreachable
19+
| ^^^^
20+
| Unreachable case
21+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:24:7 -----------------------------------------
22+
24 | case _ => // warn: unreachable
23+
| ^
24+
| Unreachable case
25+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:25:7 -----------------------------------------
26+
25 | case null => // warn: unreachable
27+
| ^^^^
28+
| Unreachable case
29+
-- [E121] Pattern Match Warning: tests/warn/redundant-null.scala:30:7 --------------------------------------------------
30+
30 | case _ => // warn: null only
31+
| ^
32+
| Unreachable case except for null (if this is intentional, consider writing case null => instead).
33+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:31:7 -----------------------------------------
34+
31 | case null => // warn: unreachable
35+
| ^^^^
36+
| Unreachable case
37+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:32:7 -----------------------------------------
38+
32 | case _ => // warn: unreachable
39+
| ^
40+
| Unreachable case
41+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:33:7 -----------------------------------------
42+
33 | case _ => // warn: unreachable
43+
| ^
44+
| Unreachable case
45+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:37:7 -----------------------------------------
46+
37 | case _ => // warn: unreachable
47+
| ^
48+
| Unreachable case
49+
-- [E030] Match case Unreachable Warning: tests/warn/redundant-null.scala:41:7 -----------------------------------------
50+
41 | case _ => // warn: unreachable
51+
| ^
52+
| Unreachable case
53+
-- [E121] Pattern Match Warning: tests/warn/redundant-null.scala:45:7 --------------------------------------------------
54+
45 | case _ => // warn: null only
55+
| ^
56+
| Unreachable case except for null (if this is intentional, consider writing case null => instead).

‎tests/warn/redundant-null.scala

Lines changed: 45 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,45 @@
1+
class A
2+
class B
3+
class C
4+
5+
val n = null
6+
7+
def f(s: A) = s match
8+
case _: n.type =>
9+
case _: A =>
10+
case _: n.type => // warn: unreachable
11+
case null =>
12+
case _ => // warn: unreachable
13+
case _ => // warn: unreachable
14+
15+
def f2(s: A | B | C) = s match
16+
case _: A => 0
17+
case _: C | null | _: B => 1
18+
case _ => 3 // warn: unreachable
19+
20+
def f3(s: A | B) = s match
21+
case _: A =>
22+
case _ =>
23+
case _: B => // warn: unreachable
24+
case _ => // warn: unreachable
25+
case null => // warn: unreachable
26+
27+
def f4(s: String | Int) = s match
28+
case _: Int =>
29+
case _: String =>
30+
case _ => // warn: null only
31+
case null => // warn: unreachable
32+
case _ => // warn: unreachable
33+
case _ => // warn: unreachable
34+
35+
def f5(x: String) = x match
36+
case x =>
37+
case _ => // warn: unreachable
38+
39+
def test(s: String | Null) = s match
40+
case ss =>
41+
case _ => // warn: unreachable
42+
43+
def test2(s: String | Null) = s match
44+
case ss: String =>
45+
case _ => // warn: null only

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