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Don't elide capture sets of capability classes in most cases
When printing types deriving from capability, do print their capture sets even if these are implied. This avoids confusing errors where a capability classes has two different implied Fresh instances which are both elided so the types look the same. Exception: When printing a singleton type (x: T) we do elide in T, since the usually the only part that matters is the `x`. But we don't do the elision under -Ycc-verbose or -explain.
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4 files changed

+46
-29
lines changed

4 files changed

+46
-29
lines changed

‎compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

+16-8
Original file line numberDiff line numberDiff line change
@@ -31,6 +31,11 @@ class PlainPrinter(_ctx: Context) extends Printer {
3131
/** Print Fresh instances as <cap hiding ...> */
3232
protected def ccVerbose = ctx.settings.YccVerbose.value
3333

34+
/** Elide redundant ^ and ^{cap.rd} when printing instances of Capability
35+
* classes. Gets set when singletons are printed as `(x: T)` to reduce verbosity.
36+
*/
37+
private var elideCapabilityCaps = false
38+
3439
private var openRecs: List[RecType] = Nil
3540

3641
protected def maxToTextRecursions: Int = 100
@@ -276,12 +281,12 @@ class PlainPrinter(_ctx: Context) extends Printer {
276281
}.close
277282
case tp @ CapturingType(parent, refs) =>
278283
val boxText: Text = Str("box ") provided tp.isBoxed //&& ctx.settings.YccDebug.value
279-
if parent.derivesFrom(defn.Caps_Capability)
280-
&& refs.containsRootCapability && refs.isReadOnly && !printDebug
281-
then
282-
toText(parent)
283-
else
284-
toTextCapturing(parent, refs, boxText)
284+
if elideCapabilityCaps
285+
&& parent.derivesFrom(defn.Caps_Capability)
286+
&& refs.containsRootCapability
287+
&& refs.isReadOnly
288+
then toText(parent)
289+
else toTextCapturing(parent, refs, boxText)
285290
case tp @ RetainingType(parent, refs) =>
286291
if Feature.ccEnabledSomewhere then
287292
toTextCapturing(parent, refs, "") ~ Str("R").provided(printDebug)
@@ -367,7 +372,11 @@ class PlainPrinter(_ctx: Context) extends Printer {
367372
}.close
368373

369374
def toTextSingleton(tp: SingletonType): Text =
370-
"(" ~ toTextRef(tp) ~ " : " ~ toTextGlobal(tp.underlying) ~ ")"
375+
val saved = elideCapabilityCaps
376+
elideCapabilityCaps = !ccVerbose && !ctx.settings.explain.value
377+
// don't elide capability capture sets under -Ycc-verbose or -explain
378+
try "(" ~ toTextRef(tp) ~ " : " ~ toTextGlobal(tp.underlying) ~ ")"
379+
finally elideCapabilityCaps = saved
371380

372381
protected def paramsText(lam: LambdaType): Text = {
373382
def paramText(ref: ParamRef) =
@@ -468,7 +477,6 @@ class PlainPrinter(_ctx: Context) extends Printer {
468477
case tp @ root.Fresh(hidden) =>
469478
val idStr = if showUniqueIds then s"#${tp.rootAnnot.id}" else ""
470479
if ccVerbose then s"<fresh$idStr in ${tp.ccOwner} hiding " ~ toTextCaptureSet(hidden) ~ ">"
471-
else if ccVerbose then "fresh"
472480
else "cap"
473481
case tp => toText(tp)
474482

‎tests/neg-custom-args/captures/effect-swaps.check

+6-4
Original file line numberDiff line numberDiff line change
@@ -17,11 +17,12 @@
1717
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/effect-swaps.scala:69:10 ---------------------------------
1818
69 | Future: fut ?=> // error, type mismatch
1919
| ^
20-
|Found: (contextual$9: boundary.Label[box Result[box Future[box T^?]^?, box E^?]^?]) ?->{fr, async}
20+
|Found: (contextual$9: boundary.Label[box Result[box Future[box T^?]^?, box E^?]^?]^{cap.rd}) ?->{fr, async}
2121
| box Future[box T^?]^{fr, contextual$9}
22-
|Required: (contextual$9: boundary.Label[Result[box Future[box T^?]^?, box E^?]]) ?=> box Future[box T^?]^?
22+
|Required: (contextual$9: boundary.Label[Result[box Future[box T^?]^?, box E^?]]^{cap.rd}) ?=> box Future[box T^?]^?
2323
|
2424
|where: ?=> refers to a fresh root capability created in method fail4 when checking argument to parameter body of method make
25+
| cap is the universal root capability
2526
|
2627
|
2728
|Note that reference contextual$9.type
@@ -32,10 +33,11 @@
3233
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/effect-swaps.scala:73:35 ---------------------------------
3334
73 | Result.make[Future[T], E]: lbl ?=> // error: type mismatch
3435
| ^
35-
|Found: (lbl: boundary.Label[box Result[box Future[box T^?]^?, box E^?]^?]) ?->{fr, async} Future[box T^?]^{fr, lbl}
36-
|Required: (lbl: boundary.Label[Result[Future[T], E]]) ?=> Future[T]
36+
|Found: (lbl: boundary.Label[box Result[box Future[box T^?]^?, box E^?]^?]^{cap.rd}) ?->{fr, async} Future[box T^?]^{fr, lbl}
37+
|Required: (lbl: boundary.Label[Result[Future[T], E]]^{cap.rd}) ?=> Future[T]
3738
|
3839
|where: ?=> refers to a fresh root capability created in method fail5 when checking argument to parameter body of method make
40+
| cap is the universal root capability
3941
74 | Future: fut ?=>
4042
75 | fr.await.ok
4143
|

‎tests/neg-custom-args/captures/extending-cap-classes.check

+8-4
Original file line numberDiff line numberDiff line change
@@ -1,15 +1,19 @@
11
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/extending-cap-classes.scala:7:15 -------------------------
22
7 | val x2: C1 = new C2 // error
33
| ^^^^^^
4-
| Found: C2
5-
| Required: C1
4+
| Found: C2^{cap.rd}
5+
| Required: C1
6+
|
7+
| where: cap is a fresh root capability created in value x2 when constructing Capability instance C2
68
|
79
| longer explanation available when compiling with `-explain`
810
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/extending-cap-classes.scala:8:15 -------------------------
911
8 | val x3: C1 = new C3 // error
1012
| ^^^^^^
11-
| Found: C3
12-
| Required: C1
13+
| Found: C3^{cap.rd}
14+
| Required: C1
15+
|
16+
| where: cap is a fresh root capability created in value x3 when constructing Capability instance C3
1317
|
1418
| longer explanation available when compiling with `-explain`
1519
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/extending-cap-classes.scala:13:15 ------------------------

‎tests/neg-custom-args/captures/scoped-caps.check

+16-13
Original file line numberDiff line numberDiff line change
@@ -62,34 +62,37 @@
6262
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scoped-caps.scala:16:24 ----------------------------------
6363
16 | val _: (x: S) -> B^ = h // error: direct conversion fails
6464
| ^
65-
| Found: (h : S -> B^)
66-
| Required: (x: S) -> B^²
65+
| Found: (h : S -> B^)
66+
| Required: (x: S^{cap.rd}) -> B^²
6767
|
68-
| where: ^ refers to a fresh root capability in the type of value h
69-
| ^² refers to a root capability associated with the result type of (x: S): B^²
68+
| where: ^ refers to a fresh root capability in the type of value h
69+
| ^² refers to a root capability associated with the result type of (x: S^{cap.rd}): B^²
70+
| cap is the universal root capability
7071
|
7172
|
72-
| Note that the existential capture root in B^
73-
| cannot subsume the capability cap
73+
| Note that the existential capture root in B^
74+
| cannot subsume the capability cap
7475
|
7576
| longer explanation available when compiling with `-explain`
7677
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scoped-caps.scala:22:19 ----------------------------------
7778
22 | val _: S -> B^ = j // error
7879
| ^
79-
| Found: (j : (x: S) -> B^)
80-
| Required: S -> B^²
80+
| Found: (j : (x: S) -> B^)
81+
| Required: S^{cap.rd} -> B^²
8182
|
82-
| where: ^ refers to a root capability associated with the result type of (x: S): B^
83-
| ^² refers to a fresh root capability in the type of value _$11
83+
| where: ^ refers to a root capability associated with the result type of (x: S^{cap.rd}): B^
84+
| ^² refers to a fresh root capability in the type of value _$11
85+
| cap is the universal root capability
8486
|
8587
| longer explanation available when compiling with `-explain`
8688
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scoped-caps.scala:23:19 ----------------------------------
8789
23 | val _: S -> B^ = x => j(x) // error
8890
| ^^^^^^^^^
89-
| Found: (x: S) ->? B^{x}
90-
| Required: (x: S) -> B^
91+
| Found: (x: S^{cap.rd}) ->? B^{x}
92+
| Required: (x: S^{cap.rd}) -> B^
9193
|
92-
| where: ^ refers to a fresh root capability in the type of value _$12
94+
| where: ^ refers to a fresh root capability in the type of value _$12
95+
| cap is the universal root capability
9396
|
9497
| longer explanation available when compiling with `-explain`
9598
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scoped-caps.scala:26:20 ----------------------------------

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