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Inferred Contextual params are less nameable #24381

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4da73cd
Inferred Contextual params are less nameable
som-snytt Nov 12, 2025
88af888
ContextFunctionParamName prefers underlying for mkString
som-snytt Nov 12, 2025
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8 changes: 5 additions & 3 deletions compiler/src/dotty/tools/dotc/ast/Desugar.scala
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Expand Up @@ -1987,10 +1987,12 @@ object desugar {
.collect:
case vd: ValDef => vd

def makeContextualFunction(formals: List[Tree], paramNamesOrNil: List[TermName], body: Tree, erasedParams: List[Boolean])(using Context): Function =
def makeContextualFunction(formals: List[Tree], paramNamesOrNil: List[TermName], body: Tree, erasedParams: List[Boolean], augmenting: Boolean = false)(using Context): Function =
val paramNames =
if paramNamesOrNil.nonEmpty then paramNamesOrNil
else formals.map(_ => ContextFunctionParamName.fresh())
if paramNamesOrNil.nonEmpty then
if augmenting then paramNamesOrNil.map(ContextFunctionParamName.fresh(_))
else paramNamesOrNil
else List.fill(formals.length)(ContextFunctionParamName.fresh())
val params = for (tpt, pname) <- formals.zip(paramNames) yield
ValDef(pname, tpt, EmptyTree).withFlags(Given | Param)
FunctionWithMods(params, body, Modifiers(Given), erasedParams)
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8 changes: 7 additions & 1 deletion compiler/src/dotty/tools/dotc/core/NameKinds.scala
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Expand Up @@ -303,12 +303,18 @@ object NameKinds {
/** The name of an inferred contextual function parameter:
*
* val x: A ?=> B = b
* val f: (x: A) ?=> B = b
*
* becomes:
*
* val x: A ?=> B = (contextual$1: A) ?=> b
* val f: (x: A) ?=> B = (xcontextual$1: A) ?=> b
*/
val ContextFunctionParamName: UniqueNameKind = new UniqueNameKind("contextual$")
val ContextFunctionParamName: UniqueNameKind =
new UniqueNameKind("contextual$"):
override def mkString(underlying: TermName, info: ThisInfo): String =
if !underlying.isEmpty then str.sanitize(underlying.toString)
else separator + info.num

/** Other unique names */
val CanThrowEvidenceName: UniqueNameKind = new UniqueNameKind("canThrow$")
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/Names.scala
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Expand Up @@ -185,7 +185,7 @@ object Names {
def info: NameInfo = SimpleNameKind.info
def underlying: TermName = unsupported("underlying")

@sharable // because of synchronized block in `and`
@sharable // because of synchronized block in `add`
private var derivedNames: LinearMap[NameInfo, DerivedName] = LinearMap.empty

private def add(info: NameInfo): TermName = synchronized {
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4 changes: 1 addition & 3 deletions compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala
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Expand Up @@ -361,9 +361,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
case tp: LazyRef =>
def refTxt =
try toTextGlobal(tp.ref)
catch {
case ex: Throwable => Str("...")
}
catch case _: Throwable => Str("...") // reconsider catching errors
"LazyRef(" ~ refTxt ~ ")"
case Range(lo, hi) =>
toText(lo) ~ ".." ~ toText(hi)
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Typer.scala
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Expand Up @@ -3912,7 +3912,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
case _ => paramTypes.map(_ => false)
}

val ifun = desugar.makeContextualFunction(paramTypes, paramNamesOrNil, tree, erasedParams)
val ifun = desugar.makeContextualFunction(paramTypes, paramNamesOrNil, tree, erasedParams, augmenting = true)
typr.println(i"make contextual function $tree / $pt ---> $ifun")
typedFunctionValue(ifun, pt)
.tap:
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6 changes: 4 additions & 2 deletions tests/neg-custom-args/captures/filevar.check
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Expand Up @@ -5,10 +5,12 @@
|The leakage occurred when trying to match the following types:
|
|Found: (l: scala.caps.Capability^) ?->'s2 File^'s3 ->'s4 Unit
|Required: (l: scala.caps.Capability^) ?-> (f: File^{l}) => Unit
|Required: (l²: scala.caps.Capability^) ?-> (f: File^{l²}) => Unit
|
|where: => refers to a root capability associated with the result type of (using l: scala.caps.Capability^): (f: File^{l}) => Unit
|where: => refers to a root capability associated with the result type of (using l²: scala.caps.Capability^): (f: File^{l²}) => Unit
| ^ refers to the universal root capability
| l is a reference to a value parameter
| l² is a reference to a value parameter
16 | val o = Service()
17 | o.file = f
18 | o.log
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10 changes: 6 additions & 4 deletions tests/neg-custom-args/captures/i15923.check
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Expand Up @@ -5,10 +5,12 @@
|The leakage occurred when trying to match the following types:
|
|Found: (lcap: scala.caps.Capability^) ?->'s2 Cap^'s3 ->'s4 Id[Cap^'s5]^'s6
|Required: (lcap: scala.caps.Capability^) ?-> Cap^{lcap} => Id[Cap^'s1]^'s7
|Required: (lcap²: scala.caps.Capability^) ?-> Cap^{lcap²} => Id[Cap^'s1]^'s7
|
|where: => refers to a root capability associated with the result type of (using lcap: scala.caps.Capability^): Cap^{lcap} => Id[Cap^'s1]^'s7
| ^ refers to the universal root capability
| cap is a root capability associated with the result type of (x$0: Cap^'s3): Id[Cap^'s5]^'s6
|where: => refers to a root capability associated with the result type of (using lcap²: scala.caps.Capability^): Cap^{lcap²} => Id[Cap^'s1]^'s7
| ^ refers to the universal root capability
| cap is a root capability associated with the result type of (x$0: Cap^'s3): Id[Cap^'s5]^'s6
| lcap is a reference to a value parameter
| lcap² is a reference to a value parameter
|
| longer explanation available when compiling with `-explain`
4 changes: 2 additions & 2 deletions tests/neg-custom-args/captures/lazyvals2.check
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@@ -1,5 +1,5 @@
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals2.scala:19:31 ------------------------------------
19 | val fun2: () ->{io} String = () => x() // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals2.scala:20:31 ------------------------------------
20 | val fun2: () ->{io} String = () => x() // error
| ^^^^^^^^^
| Found: () ->{console, io} String
| Required: () ->{io} String
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1 change: 1 addition & 0 deletions tests/neg-custom-args/captures/lazyvals2.scala
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@@ -1,3 +1,4 @@
//> using options -Yimports:scala,scala.Predef
import language.experimental.captureChecking
import caps.*

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28 changes: 14 additions & 14 deletions tests/neg-custom-args/captures/lazyvals5.check
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@@ -1,59 +1,59 @@
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:31:41 ------------------------------------
31 | val v0: () -> () ->{io} String = () => t.memberLazy // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:32:41 ------------------------------------
32 | val v0: () -> () ->{io} String = () => t.memberLazy // error
| ^^^^^^^^^^^^^^^^^^
| Found: () ->{t} () ->{io} String
| Required: () -> () ->{io} String
|
| Note that capability t is not included in capture set {}.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:33:41 ------------------------------------
33 | val v1: () -> String = () => t.memberLazy() // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:34:41 ------------------------------------
34 | val v1: () -> String = () => t.memberLazy() // error
| ^^^^^^^^^^^^^^^^^^^^
| Found: () ->{t} String
| Required: () -> String
|
| Note that capability t is not included in capture set {}.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:35:41 ------------------------------------
35 | val v3: (() -> String)^{c.console} = () => c.memberLazy() // error (but should this be allowed?)
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:36:41 ------------------------------------
36 | val v3: (() -> String)^{c.console} = () => c.memberLazy() // error (but should this be allowed?)
| ^^^^^^^^^^^^^^^^^^^^
| Found: () ->{c} String
| Required: () ->{c.console} String
|
| Note that capability c is not included in capture set {c.console}.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:36:41 ------------------------------------
36 | val v4: () -> String = () => t.memberMethod() // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:37:41 ------------------------------------
37 | val v4: () -> String = () => t.memberMethod() // error
| ^^^^^^^^^^^^^^^^^^^^^^
| Found: () ->{t} String
| Required: () -> String
|
| Note that capability t is not included in capture set {}.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:39:28 ------------------------------------
39 | val v6: () ->{c} String = () => funky // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:40:28 ------------------------------------
40 | val v6: () ->{c} String = () => funky // error
| ^^^^^^^^^^^
| Found: () ->{t, c} String
| Required: () ->{c} String
|
| Note that capability t is not included in capture set {c}.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:40:30 ------------------------------------
40 | val v6_1: () ->{t} String = () => funky // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:41:30 ------------------------------------
41 | val v6_1: () ->{t} String = () => funky // error
| ^^^^^^^^^^^
| Found: () ->{t, c} String
| Required: () ->{t} String
|
| Note that capability c is not included in capture set {t}.
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:60:55 ------------------------------------
60 | val v9: () ->{c2.memberLazy, t2.memberLazy} String = () => funky2 // error (but should this be allowed?)
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/lazyvals5.scala:61:55 ------------------------------------
61 | val v9: () ->{c2.memberLazy, t2.memberLazy} String = () => funky2 // error (but should this be allowed?)
| ^^^^^^^^^^^^
| Found: () ->{t2, c2} String
| Required: () ->{c2.memberLazy, t2.memberLazy²} String
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3 changes: 2 additions & 1 deletion tests/neg-custom-args/captures/lazyvals5.scala
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@@ -1,3 +1,4 @@
//> using options -Yimports:scala,scala.Predef
import language.experimental.captureChecking
import caps.*

Expand Down Expand Up @@ -60,4 +61,4 @@ def client(c: Clazz^): Unit =
val v9: () ->{c2.memberLazy, t2.memberLazy} String = () => funky2 // error (but should this be allowed?)
val v10: () ->{t2, c2} String = () => funky2 // ok

()
()
68 changes: 34 additions & 34 deletions tests/neg-custom-args/captures/scope-extrusions.check
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@@ -1,17 +1,17 @@
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:9:8 -------------------------------
9 | v = x // error
| ^
| Found: (x : IO)
| Required: IO^
|
| Note that capability x is not included in capture set {cap}
| because (x : IO) in method f1 is not visible from cap in variable v.
|
| where: ^ and cap refer to a fresh root capability classified as SharedCapability in the type of variable v
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:10:8 ------------------------------
10 | w = g // error
10 | v = x // error
| ^
| Found: (x : IO)
| Required: IO^
|
| Note that capability x is not included in capture set {cap}
| because (x : IO) in method f1 is not visible from cap in variable v.
|
| where: ^ and cap refer to a fresh root capability classified as SharedCapability in the type of variable v
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:11:8 ------------------------------
11 | w = g // error
| ^
| Found: () ->{x} Unit
| Required: () => Unit
Expand All @@ -22,8 +22,8 @@
| where: => and cap refer to a fresh root capability in the type of variable w
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:19:11 -----------------------------
19 | withFile(io => io) // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:20:11 -----------------------------
20 | withFile(io => io) // error
| ^^^^^^^^
|Capability io outlives its scope: it leaks into outer capture set 's1 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -35,8 +35,8 @@
| ^ refers to the universal root capability
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:20:11 -----------------------------
20 | withFile(id) // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:21:11 -----------------------------
21 | withFile(id) // error
| ^^
|Capability x outlives its scope: it leaks into outer capture set 's4 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -48,8 +48,8 @@
| ^ refers to the universal root capability
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:21:11 -----------------------------
21 | withFile(x => id(x)) // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:22:11 -----------------------------
22 | withFile(x => id(x)) // error
| ^^^^^^^^^^
|Capability x outlives its scope: it leaks into outer capture set 's6 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -61,8 +61,8 @@
| ^ refers to the universal root capability
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:22:11 -----------------------------
22 | withFile(id2) // error, note mentions cap since we never have a more specific include failure
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:23:11 -----------------------------
23 | withFile(id2) // error, note mentions cap since we never have a more specific include failure
| ^^^
|Capability cap outlives its scope: it leaks into outer capture set 's9 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -76,8 +76,8 @@
| cap is a root capability associated with the result type of (x: IO^): IO^'s9
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:23:11 -----------------------------
23 | withFile(x => id2(x)) // error, note mentions cap since we never have a more specific include failure
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:24:11 -----------------------------
24 | withFile(x => id2(x)) // error, note mentions cap since we never have a more specific include failure
| ^^^^^^^^^^^
|Capability cap outlives its scope: it leaks into outer capture set 's11 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -91,8 +91,8 @@
| cap is a root capability associated with the result type of (x: IO^²): IO^'s11
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:24:11 -----------------------------
24 | withFile(identity) // error, note mentions cap since we never have a more specific include failure
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:25:11 -----------------------------
25 | withFile(identity) // error, note mentions cap since we never have a more specific include failure
| ^^^^^^^^
|Capability cap outlives its scope: it leaks into outer capture set 's14 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -105,8 +105,8 @@
| cap is a root capability associated with the result type of (x: IO^): IO^'s14
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:25:11 -----------------------------
25 | withFile(x => identity(x)) // error, note mentions cap since we never have a more specific include failure
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:26:11 -----------------------------
26 | withFile(x => identity(x)) // error, note mentions cap since we never have a more specific include failure
| ^^^^^^^^^^^^^^^^
|Capability cap outlives its scope: it leaks into outer capture set 's18 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -119,8 +119,8 @@
| cap is a root capability associated with the result type of (x: IO^): IO^'s18
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:27:12 -----------------------------
27 | withFile: io => // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:28:12 -----------------------------
28 | withFile: io => // error
| ^
|Capability io outlives its scope: it leaks into outer capture set 's22 which is owned by method test.
|The leakage occurred when trying to match the following types:
Expand All @@ -130,11 +130,11 @@
|
|where: => refers to a fresh root capability created in method test when checking argument to parameter op of method withFile
| ^ refers to the universal root capability
28 | () => println(io)
29 | () => println(io)
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:30:21 -----------------------------
30 | val f2: IO => IO = (x: IO) => x // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:31:21 -----------------------------
31 | val f2: IO => IO = (x: IO) => x // error
| ^^^^^^^^^^^^
| Found: (x: IO^) ->'s25 IO^{x}
| Required: IO^ => IO^²
Expand All @@ -147,8 +147,8 @@
| ^² and cap refer to a fresh root capability classified as SharedCapability in the type of value f2
|
| longer explanation available when compiling with `-explain`
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:32:21 -----------------------------
32 | val f4: IO => IO = f3 // error
-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/scope-extrusions.scala:33:21 -----------------------------
33 | val f4: IO => IO = f3 // error
| ^^
| Found: (f3 : (x$0: IO) ->{} IO^{x$0})
| Required: IO^ => IO^²
Expand Down
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