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Check Any-typed if/match in toString lint #11074

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Check Any-typed if/match in toString lint #11074

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17 changes: 14 additions & 3 deletions src/compiler/scala/tools/reflect/FastStringInterpolator.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -106,11 +106,22 @@ trait FastStringInterpolator extends FormatInterpolator {
val emptyLit = treatedContents.isEmpty
if (i < numLits - 1) {
val arg = argsIndexed(i)
if (linting && !(arg.tpe =:= definitions.StringTpe))
def warn(msg: String) = runReporting.warning(arg.pos, msg, WFlagTostringInterpolated, c.internal.enclosingOwner)
def stringlyBranches = arg match {
case If(_, thenp, elsep) => thenp.tpe <:< definitions.StringTpe && elsep.tpe <:< definitions.StringTpe
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@lrytz lrytz Jun 16, 2025 •
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non-unit primitives should be allowed

scala> def f(b: Boolean) = s"b: ${if (b) 1 else 0}"
                                  ^
       warning: interpolation uses toString
def f(b: Boolean): String

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Also nesting..

scala> def f(x: Any) = s"r: ${ x match { case s: String => s; case _ => if (x == null) "n" else "s" } }"
                                 ^
       warning: interpolation uses toString

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Thanks I guess!

case Match(_, cases) =>
cases.forall {
case CaseDef(_, _, body) => body.tpe <:< definitions.StringTpe
}
case _ => false
}
if (linting && !(arg.tpe =:= definitions.StringTpe)) // literals are widened, so include Null, Nothing
if (arg.tpe.typeSymbol eq definitions.UnitClass)
runReporting.warning(arg.pos, "interpolated Unit value", WFlagTostringInterpolated, c.internal.enclosingOwner)
warn("interpolated Unit value")
else if ((arg.tpe.typeSymbol eq definitions.AnyClass) && stringlyBranches)
() // if or match assumes expected type Any of interpolated expression, check branches are strings
else if (!definitions.isPrimitiveValueType(arg.tpe))
runReporting.warning(arg.pos, "interpolation uses toString", WFlagTostringInterpolated, c.internal.enclosingOwner)
warn("interpolation uses toString")
concatArgs += arg
}
if (!emptyLit) concatArgs += lit
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51 changes: 26 additions & 25 deletions test/files/neg/tostring-interpolated.check
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@@ -1,41 +1,42 @@
tostring-interpolated.scala:7: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.f
tostring-interpolated.scala:8: warning: interpolation uses toString
def f = f"$c" // warn
^
tostring-interpolated.scala:8: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.s
tostring-interpolated.scala:9: warning: interpolation uses toString
def s = s"$c" // warn
^
tostring-interpolated.scala:9: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.r
tostring-interpolated.scala:10: warning: interpolation uses toString
def r = raw"$c" // warn
^
tostring-interpolated.scala:11: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.format
tostring-interpolated.scala:12: warning: interpolation uses toString
def format = f"${c.x}%d in $c or $c%s" // warn using c.toString // warn
^
tostring-interpolated.scala:11: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.format
tostring-interpolated.scala:12: warning: interpolation uses toString
def format = f"${c.x}%d in $c or $c%s" // warn using c.toString // warn
^
tostring-interpolated.scala:13: warning: Boolean format is null test for non-Boolean
def bool = f"$c%b" // warn just a null check
^
tostring-interpolated.scala:15: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.oops
def oops = s"${null} slipped thru my fingers" // warn
^
tostring-interpolated.scala:20: error: interpolation uses toString
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=T.greeting
tostring-interpolated.scala:17: warning: interpolation uses toString
def greeting = s"$sb, world" // warn
^
tostring-interpolated.scala:31: error: interpolated Unit value
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=Mitigations.unitized
tostring-interpolated.scala:21: warning: Boolean format is null test for non-Boolean
def bool = f"$c%b" // warn just a null check (quirk of Java format)
^
tostring-interpolated.scala:23: warning: interpolation uses toString
def oops = s"${null} slipped thru my fingers" // warn although conforms to String
^
tostring-interpolated.scala:25: warning: interpolation uses toString
def exceptionally = s"Hello, ${???}" // warn although conforms to String
^
tostring-interpolated.scala:36: warning: interpolated Unit value
def unitized = s"unfortunately $shown" // warn accidental unit value
^
tostring-interpolated.scala:32: error: interpolated Unit value
Applicable -Wconf / @nowarn filters for this fatal warning: msg=<part of the message>, cat=w-flag-tostring-interpolated, site=Mitigations.funitized
tostring-interpolated.scala:37: warning: interpolated Unit value
def funitized = f"unfortunately $shown" // warn accidental unit value
^
1 warning
9 errors
tostring-interpolated.scala:53: warning: interpolation uses toString
val greeting = s"Hello ${if (shouldCaps) "WORLD" else world}" // warn
^
tostring-interpolated.scala:64: warning: interpolation uses toString
val greeting = s"Hello ${x match { case 42 => "WORLD" case 27 => world case _ => ??? }}" // warn
^
error: No warnings can be incurred under -Werror.
13 warnings
1 error
48 changes: 42 additions & 6 deletions test/files/neg/tostring-interpolated.scala
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@@ -1,4 +1,5 @@
//> using options -Wconf:cat=w-flag-tostring-interpolated:e -Wtostring-interpolated
//> using options -Werror -Wtostring-interpolated
///> using options -Wconf:cat=w-flag-tostring-interpolated:e -Wtostring-interpolated

case class C(x: Int)

Expand All @@ -10,21 +11,25 @@ trait T {

def format = f"${c.x}%d in $c or $c%s" // warn using c.toString // warn

def bool = f"$c%b" // warn just a null check

def oops = s"${null} slipped thru my fingers" // warn

def ok = s"${c.toString}"

def sb = new StringBuilder().append("hello")
def greeting = s"$sb, world" // warn

def literally = s"Hello, ${"world"}" // nowarn literal, widened to String

def bool = f"$c%b" // warn just a null check (quirk of Java format)

def oops = s"${null} slipped thru my fingers" // warn although conforms to String

def exceptionally = s"Hello, ${???}" // warn although conforms to String
}

class Mitigations {

val s = "hello, world"
val i = 42
def shown() = println("shown")
def shown = println("shown") // nowarn parenless Unit def because that is at refchecks

def ok = s"$s is ok"
def jersey = s"number $i"
Expand All @@ -34,3 +39,34 @@ class Mitigations {
def nopct = f"$s is ok"
def nofmt = f"number $i"
}

class Branches {

class C {
val shouldCaps = true
val greeting = s"Hello ${if (shouldCaps) "WORLD" else "world"}"
}

class D {
val shouldCaps = true
object world { override def toString = "world" }
val greeting = s"Hello ${if (shouldCaps) "WORLD" else world}" // warn
}

class E {
def x = 42
val greeting = s"Hello ${x match { case 42 => "WORLD" case 27 => "world" case _ => ??? }}"
}

class F {
def x = 42
object world { override def toString = "world" }
val greeting = s"Hello ${x match { case 42 => "WORLD" case 27 => world case _ => ??? }}" // warn
}

class Z {
val shouldCaps = true
val greeting = s"Hello ${if (shouldCaps) ??? else null}" // nowarn quirk, no string result
}

}