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Find more looping implicits #15481

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Jun 20, 2022
Merged

Find more looping implicits #15481

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a008ca2
Find more looping implicits
odersky Jun 19, 2022
cbdf40a
Update check file
odersky Jun 19, 2022
af4c365
Add doc comment that explains what checkLooingImplicits does
odersky Jun 20, 2022
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26 changes: 23 additions & 3 deletions compiler/src/dotty/tools/dotc/transform/CheckLoopingImplicits.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -6,13 +6,28 @@ import MegaPhase.MiniPhase
import Contexts.*, Types.*, Symbols.*, SymDenotations.*, Flags.*
import ast.*
import Decorators.*

import StdNames.*

object CheckLoopingImplicits:
val name: String = "checkLoopingImplicits"
val description: String = "check that implicit defs do not call themselves in an infinite loop"

/** Checks that implicit defs do not call themselves in an infinite loop */
/** Checks that some definitions do not call themselves in an infinite loop
* This is an incomplete check, designed to catch some likely bugs instead
* of being exhaustive. The situations where infinite loops are diagnosed are
* 1. A given method should not directly call itself
* 2. An apply method in a given object should not directly call itself
* 3. A lazy val should not directly force itself
* 4. An extension method should not directly call itself
*
* In all these cases, there are some situations which would not lead to
* an infinite loop at runtime. For instance, the call could go at runtime to an
* overriding version of the method or val which breaks the loop. That's why
* this phase only issues warnings, not errors, and also why we restrict
* checks to the 4 cases above, where a recursion is somewhat hidden.
* There are also other more complicated calling patterns that could also
* be diagnosed as loops with more effort. This could be improved in the future.
*/
class CheckLoopingImplicits extends MiniPhase:
thisPhase =>
import tpd._
Expand Down Expand Up @@ -60,6 +75,9 @@ class CheckLoopingImplicits extends MiniPhase:
case Block(stats, expr) =>
stats.foreach(checkNotLooping)
checkNotLooping(expr)
case Inlined(_, bindings, expr) =>
bindings.foreach(checkNotLooping)
checkNotLooping(expr)
case Typed(expr, _) =>
checkNotLooping(expr)
case Assign(lhs, rhs) =>
Expand All @@ -84,7 +102,9 @@ class CheckLoopingImplicits extends MiniPhase:
checkNotLooping(t.rhs)
case _ =>

if sym.isOneOf(GivenOrImplicit | Lazy | ExtensionMethod) then
if sym.isOneOf(GivenOrImplicit | Lazy | ExtensionMethod)
|| sym.name == nme.apply && sym.owner.is(Module) && sym.owner.sourceModule.isOneOf(GivenOrImplicit)
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@julienrf julienrf Jun 20, 2022 •
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Could you please add a comment to explain the intent behind the condition on the right side of the ||? I wonder if this condition is too strong, but I am not sure. Do we have existing “pos” tests (the PR only contains two “neg” tests)?

then
checkNotLooping(mdef.rhs)
mdef
end transform
Expand Down
16 changes: 16 additions & 0 deletions tests/neg-custom-args/fatal-warnings/i15474.scala
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@@ -0,0 +1,16 @@
import scala.language.implicitConversions

object Test1:
given c: Conversion[ String, Int ] with
def apply(from: String): Int = from.toInt // error

object Test2:
given c: Conversion[ String, Int ] = _.toInt // loop not detected, could be used as a fallback to avoid the warning.

object Prices {
opaque type Price = BigDecimal

object Price{
given Ordering[Price] = summon[Ordering[BigDecimal]] // error
}
}
132 changes: 132 additions & 0 deletions tests/neg/i13044.check
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@@ -1,3 +1,135 @@
-- Warning: tests/neg/i13044.scala:50:40 -------------------------------------------------------------------------------
50 | implicit def typeSchema: Schema[A] = Schema.gen // error // error
| ^^^^^^^^^^
|Infinite loop in function body
|{
| val SchemaDerivation_this: Schema.type = Schema
| {
| val SchemaDerivation_this: (SchemaDerivation_this : Schema.type) = SchemaDerivation_this
| {
| val $scrutinee1:
| scala.deriving.Mirror.Product{
| MirroredMonoType = A; MirroredType = A; MirroredLabel = ("A" : String); MirroredElemTypes = (A, B);
| MirroredElemLabels = (("a" : String), ("b" : String))
| }
| =
| A.$asInstanceOf[
| scala.deriving.Mirror.Product{
| MirroredMonoType = A; MirroredType = A; MirroredLabel = ("A" : String); MirroredElemTypes = (A, B);
| MirroredElemLabels = (("a" : String), ("b" : String))
| }
| ]
| val m:
| scala.deriving.Mirror.Product{
| MirroredMonoType = A; MirroredType = A; MirroredLabel = ("A" : String); MirroredElemTypes = (A, B);
| MirroredElemLabels = (("a" : String), ("b" : String))
| }
| = $scrutinee1
| lazy val fields: List[Schema[Any]] =
| {
| val SchemaDerivation_this: (SchemaDerivation_this : (SchemaDerivation_this : Schema.type)) =
| SchemaDerivation_this
| {
| val builder: Schema[Any] = TestApp.typeSchema.asInstanceOf[Schema[Any]]
| {
| val SchemaDerivation_this:
| (SchemaDerivation_this : (SchemaDerivation_this : (SchemaDerivation_this : Schema.type)))
| = SchemaDerivation_this
| (
| {
| val builder: Schema[Any] =
| {
| val SchemaDerivation_this: Schema.type = Schema
| (
| {
| val SchemaDerivation_this: (SchemaDerivation_this : Schema.type) = SchemaDerivation_this
| {
| val $scrutinee4:
| scala.deriving.Mirror.Product{
| MirroredMonoType = B; MirroredType = B; MirroredLabel = ("B" : String);
| MirroredElemTypes = C *: EmptyTuple.type
| ; MirroredElemLabels = ("c" : String) *: EmptyTuple.type
| }
| =
| B.$asInstanceOf[
| scala.deriving.Mirror.Product{
| MirroredMonoType = B; MirroredType = B; MirroredLabel = ("B" : String);
| MirroredElemTypes = C *: EmptyTuple.type
| ; MirroredElemLabels = ("c" : String) *: EmptyTuple.type
| }
| ]
| val m:
| scala.deriving.Mirror.Product{
| MirroredMonoType = B; MirroredType = B; MirroredLabel = ("B" : String);
| MirroredElemTypes = C *: EmptyTuple.type
| ; MirroredElemLabels = ("c" : String) *: EmptyTuple.type
| }
| = $scrutinee4
| lazy val fields: List[Schema[Any]] =
| {
| val SchemaDerivation_this:
| (SchemaDerivation_this : (SchemaDerivation_this : Schema.type))
| = SchemaDerivation_this
| {
| val builder: Schema[Any] =
| {
| val SchemaDerivation_this: Schema.type = Schema
| (
| {
| val SchemaDerivation_this: (...SchemaDerivation_this : ....type) =
| SchemaDerivation_this
| {
| val $scrutinee6:
| ...{
| MirroredMonoType...; MirroredType...; MirroredLabel...;
| MirroredElemTypes...
| ; MirroredElemLabels...
| }
| = ....$asInstanceOf[...]
| val m: ... = ...$scrutinee6
| lazy val fields: ... =
| {
| val SchemaDerivation_this: ... = ...
| ...:...
| }
| {
| final class $anon() extends ...(), ... {
| def build: ... = ...
| }
| ...():...
| }
| }:...[...]
| }
| :Schema[C])
| }.asInstanceOf[Schema[Any]]
| SchemaDerivation_this.recurse[EmptyTuple.type].::[Schema[Any]](builder)
| }:List[Schema[Any]]
| }
| {
| final class $anon() extends Object(), Schema[B] {
| def build: B = ???
| }
| new Object with Schema[B] {...}():Schema[B]
| }
| }:Schema[B]
| }
| :Schema[B])
| }.asInstanceOf[Schema[Any]]
| SchemaDerivation_this.recurse[EmptyTuple.type].::[Schema[Any]](builder)
| }
| :List[Schema[Any]])
| }.::[Schema[Any]](builder)
| }:List[Schema[Any]]
| }
| {
| final class $anon() extends Object(), Schema[A] {
| def build: A = ???
| }
| new Object with Schema[A] {...}():Schema[A]
| }
| }:Schema[A]
| }:Schema[A]
|}
-- Error: tests/neg/i13044.scala:50:40 ---------------------------------------------------------------------------------
50 | implicit def typeSchema: Schema[A] = Schema.gen // error // error
| ^^^^^^^^^^
Expand Down