warn on implicit def without explicit result type #5265

scabug · 2011-12-03T17:14:37Z

The following code snipet : https://gist.github.com/1427587
does not compile.

import java.util.Date

trait TDate 

trait TT[A1,T1]

trait TTFactory[F,G] {
  def create(f: F) : TT[F,G]
  def sample: F
}

object Impls {

  // If the c1 is declared before c2, it compiles fine
  // or if the implicit's result type is specified explicitly
  implicit def c2(s: Date)/* : TT[Date, TDate] */ = c1.create(s)  

  implicit val c1 = new TTFactory[Date,TDate] {
    def create(v: Date): TT[Date,TDate] = sys.error("")
    def sample = new Date
  }
}

scabug · 2011-12-03T17:14:37Z

Imported From: https://issues.scala-lang.org/browse/SI-5265?orig=1
Reporter: maxime.levesque
Affected Versions: 2.9.1
See #5348, #2206, #801

scabug · 2012-06-11T13:25:25Z

@adriaanm said:
see #2206, #801 and a plethora of duplicates

scabug · 2012-07-03T15:06:10Z

@adriaanm said:
warn unless enabled by feature flag

scabug · 2014-10-10T07:06:54Z

@retronym said:
I have a feeling there actually isn't a cycle in this example. Even if there is, we should report it.

Instead, I think the problem here is that typedBlock can trigger a type completion which causes the typedBlock for the same block to be reentered. Crucially, this happens after the DefTrees in the block have the symbols assigned. In the second run through typedBlock, the namer sees the attributed trees and decides not to enter them in scope.

The presentation compiler has a more robust namer to account for the sort of symptom, as caused by cancellation. I've moved that in to the regular namer in this WIP branch.

https://github.com/retronym/scala/tree/ticket/5265

That said, I definetely agree we should also have a warning / migration for unannotated implicits.

scabug · 2014-10-10T07:34:11Z

@retronym said:
That branch fails on (at least)

// t4716.scala
trait Bug2[ +A] extends TraversableOnce[A] {
  def ++[B >: A](that: TraversableOnce[B]) = {
    lazy val it = that.toIterator
    it
  }
}

I'm going to park this ticket again.

SethTisue · 2022-07-19T22:05:47Z

This'd be a great project for somebody.

It has increased significance lately given that Scala 3 requires the explicit result type:

scala> implicit def x = 3
-- Error: ----------------------------------------------------------------------
1 |implicit def x = 3
  |             ^
  |           result type of implicit definition needs to be given explicitly
1 error found

So I would say that -Xlint should warn about this by default (since including explicit result types has been known at least since 2011 to be good practice), and -Xsource:3 should turn that warning into error.

Is there a volunteer who would like to tackle it?

sjrd · 2022-07-19T23:32:22Z

To whoever would like to take this on, note that the warning should not apply to local definitions, i.e., those for which sym.isLocalToBlock is true. Such definitions are only visible after they're defined, and hence doing cause problematic cycles. Early experimentation in dotty discovered that they had to be allowed to preserve reasonable code patterns.

som-snytt · 2022-07-20T18:51:40Z

This'd be a great project for somebody.

Possible typo for Som, homebody. Or is that a portmanteau?

som-snytt · 2022-07-21T00:37:02Z

Possible noise reduction if it accepted

implicit def f = foo.asInstanceOf[Bar]
implicit def g = foo: Bar

The first form, in particular, adds information. The second could be transposed.

The current exemption is for override in Scala 3/-Xsource:3.

… `Implicit definition should have explicit type` ### What changes were proposed in this pull request? This PR aims to fix `Implicit definition should have explicit type` in Scala 2.13. This pr includes: 1. Declaration types for global variables of implicit 2. Add scala.annotation.warn ### Why are the changes needed? - For implicit global variables without explicit type declaration, will get warnning : warning: Implicit definition should have explicit type (inferred String) [quickfixable] - No modifications are required for local variables. Additionally, to handle cases involving reflection-related types like ClassTag in implicit variables, the [scala.annotation.warn](https://github.com/scala.annotation.warn) annotation is used to suppress the warning. Furthermore, warnings generated in Spark will be treated as errors: [error] ... Implicit definition should have explicit type (inferred org.json4s.DefaultFormats.type) [quickfixable] ... [error] implicit val formats = org.json4s.DefaultFormats Jira link: SPARK-45314: https://issues.apache.org/jira/browse/SPARK-45629 Related issue link about `implicit` : scala/bug#5265 ### Does this PR introduce _any_ user-facing change? no ### How was this patch tested? Most of the testing is completed through CI, and the example module is locally compiled and tested in IDEA Additionally, there are some writing changes that are verified through demo code ### Was this patch authored or co-authored using generative AI tooling? no Closes #43526 from laglangyue/SPARK-45629. Lead-authored-by: tangjiafu <jiafu.tang@qq.com> Co-authored-by: tangjiafu <tangjiafu@corp.netease.com> Signed-off-by: yangjie01 <yangjie01@baidu.com>

… `Implicit definition should have explicit type` ### What changes were proposed in this pull request? This PR aims to fix `Implicit definition should have explicit type` in Scala 2.13. This pr includes: 1. Declaration types for global variables of implicit 2. Add scala.annotation.warn ### Why are the changes needed? - For implicit global variables without explicit type declaration, will get warnning : warning: Implicit definition should have explicit type (inferred String) [quickfixable] - No modifications are required for local variables. Additionally, to handle cases involving reflection-related types like ClassTag in implicit variables, the [scala.annotation.warn](https://github.com/scala.annotation.warn) annotation is used to suppress the warning. Furthermore, warnings generated in Spark will be treated as errors: [error] ... Implicit definition should have explicit type (inferred org.json4s.DefaultFormats.type) [quickfixable] ... [error] implicit val formats = org.json4s.DefaultFormats Jira link: SPARK-45314: https://issues.apache.org/jira/browse/SPARK-45629 Related issue link about `implicit` : scala/bug#5265 ### Does this PR introduce _any_ user-facing change? no ### How was this patch tested? Most of the testing is completed through CI, and the example module is locally compiled and tested in IDEA Additionally, there are some writing changes that are verified through demo code ### Was this patch authored or co-authored using generative AI tooling? no Closes apache#43526 from laglangyue/SPARK-45629. Lead-authored-by: tangjiafu <jiafu.tang@qq.com> Co-authored-by: tangjiafu <tangjiafu@corp.netease.com> Signed-off-by: yangjie01 <yangjie01@baidu.com>

… `Implicit definition should have explicit type` ### What changes were proposed in this pull request? This PR aims to fix `Implicit definition should have explicit type` in Scala 2.13. This pr includes: 1. Declaration types for global variables of implicit 2. Add scala.annotation.warn ### Why are the changes needed? - For implicit global variables without explicit type declaration, will get warnning : warning: Implicit definition should have explicit type (inferred String) [quickfixable] - No modifications are required for local variables. Additionally, to handle cases involving reflection-related types like ClassTag in implicit variables, the [scala.annotation.warn](https://github.com/scala.annotation.warn) annotation is used to suppress the warning. Furthermore, warnings generated in Spark will be treated as errors: [error] ... Implicit definition should have explicit type (inferred org.json4s.DefaultFormats.type) [quickfixable] ... [error] implicit val formats = org.json4s.DefaultFormats Jira link: SPARK-45314: https://issues.apache.org/jira/browse/SPARK-45629 Related issue link about `implicit` : scala/bug#5265 ### Does this PR introduce _any_ user-facing change? no ### How was this patch tested? Most of the testing is completed through CI, and the example module is locally compiled and tested in IDEA Additionally, there are some writing changes that are verified through demo code ### Was this patch authored or co-authored using generative AI tooling? no Closes apache#43526 from laglangyue/SPARK-45629. Lead-authored-by: tangjiafu <jiafu.tang@qq.com> Co-authored-by: tangjiafu <tangjiafu@corp.netease.com> Signed-off-by: yangjie01 <yangjie01@baidu.com> # Conflicts: # connector/connect/common/src/main/scala/org/apache/spark/sql/connect/client/GrpcExceptionConverter.scala # core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala # pom.xml # project/SparkBuild.scala # sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala # sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/OperatorStateMetadata.scala

set scala dependencies for 2.13 fix delta-core to delta-spark fix for scala 2.13 [SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES] Fix `Implicit definition should have explicit type` ### What changes were proposed in this pull request? This PR aims to fix `Implicit definition should have explicit type` in Scala 2.13. This pr includes: 1. Declaration types for global variables of implicit 2. Add scala.annotation.warn ### Why are the changes needed? - For implicit global variables without explicit type declaration, will get warnning : warning: Implicit definition should have explicit type (inferred String) [quickfixable] - No modifications are required for local variables. Additionally, to handle cases involving reflection-related types like ClassTag in implicit variables, the [scala.annotation.warn](https://github.com/scala.annotation.warn) annotation is used to suppress the warning. Furthermore, warnings generated in Spark will be treated as errors: [error] ... Implicit definition should have explicit type (inferred org.json4s.DefaultFormats.type) [quickfixable] ... [error] implicit val formats = org.json4s.DefaultFormats Jira link: SPARK-45314: https://issues.apache.org/jira/browse/SPARK-45629 Related issue link about `implicit` : scala/bug#5265 ### Does this PR introduce _any_ user-facing change? no ### How was this patch tested? Most of the testing is completed through CI, and the example module is locally compiled and tested in IDEA Additionally, there are some writing changes that are verified through demo code ### Was this patch authored or co-authored using generative AI tooling? no Closes apache#43526 from laglangyue/SPARK-45629. Lead-authored-by: tangjiafu <jiafu.tang@qq.com> Co-authored-by: tangjiafu <tangjiafu@corp.netease.com> Signed-off-by: yangjie01 <yangjie01@baidu.com> # Conflicts: # connector/connect/common/src/main/scala/org/apache/spark/sql/connect/client/GrpcExceptionConverter.scala # core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala # pom.xml # project/SparkBuild.scala # sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala # sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/OperatorStateMetadata.scala Revert "[SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES] Fix `Implicit definition should have explicit type`" This reverts commit bc67612. Fix Implicit definition should have explicit type fix install error add args for scala 2.13 fix args update pom java version update pom jvm target version fix implicit types rollback scala 2.13.8 rollback fmt blank space fix

set scala dependencies for 2.13 fix delta-core to delta-spark fix for scala 2.13 [SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES] Fix `Implicit definition should have explicit type` ### What changes were proposed in this pull request? This PR aims to fix `Implicit definition should have explicit type` in Scala 2.13. This pr includes: 1. Declaration types for global variables of implicit 2. Add scala.annotation.warn ### Why are the changes needed? - For implicit global variables without explicit type declaration, will get warnning : warning: Implicit definition should have explicit type (inferred String) [quickfixable] - No modifications are required for local variables. Additionally, to handle cases involving reflection-related types like ClassTag in implicit variables, the [scala.annotation.warn](https://github.com/scala.annotation.warn) annotation is used to suppress the warning. Furthermore, warnings generated in Spark will be treated as errors: [error] ... Implicit definition should have explicit type (inferred org.json4s.DefaultFormats.type) [quickfixable] ... [error] implicit val formats = org.json4s.DefaultFormats Jira link: SPARK-45314: https://issues.apache.org/jira/browse/SPARK-45629 Related issue link about `implicit` : scala/bug#5265 ### Does this PR introduce _any_ user-facing change? no ### How was this patch tested? Most of the testing is completed through CI, and the example module is locally compiled and tested in IDEA Additionally, there are some writing changes that are verified through demo code ### Was this patch authored or co-authored using generative AI tooling? no Closes apache#43526 from laglangyue/SPARK-45629. Lead-authored-by: tangjiafu <jiafu.tang@qq.com> Co-authored-by: tangjiafu <tangjiafu@corp.netease.com> Signed-off-by: yangjie01 <yangjie01@baidu.com> # Conflicts: # connector/connect/common/src/main/scala/org/apache/spark/sql/connect/client/GrpcExceptionConverter.scala # core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala # pom.xml # project/SparkBuild.scala # sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala # sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/OperatorStateMetadata.scala Revert "[SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES] Fix `Implicit definition should have explicit type`" This reverts commit bc67612. Fix Implicit definition should have explicit type fix install error add args for scala 2.13 fix args update pom java version update pom jvm target version fix implicit types rollback scala 2.13.8 rollback fmt blank space fix fix import fmt

set scala dependencies for 2.13 fix delta-core to delta-spark fix for scala 2.13 [SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES] Fix `Implicit definition should have explicit type` ### What changes were proposed in this pull request? This PR aims to fix `Implicit definition should have explicit type` in Scala 2.13. This pr includes: 1. Declaration types for global variables of implicit 2. Add scala.annotation.warn ### Why are the changes needed? - For implicit global variables without explicit type declaration, will get warnning : warning: Implicit definition should have explicit type (inferred String) [quickfixable] - No modifications are required for local variables. Additionally, to handle cases involving reflection-related types like ClassTag in implicit variables, the [scala.annotation.warn](https://github.com/scala.annotation.warn) annotation is used to suppress the warning. Furthermore, warnings generated in Spark will be treated as errors: [error] ... Implicit definition should have explicit type (inferred org.json4s.DefaultFormats.type) [quickfixable] ... [error] implicit val formats = org.json4s.DefaultFormats Jira link: SPARK-45314: https://issues.apache.org/jira/browse/SPARK-45629 Related issue link about `implicit` : scala/bug#5265 ### Does this PR introduce _any_ user-facing change? no ### How was this patch tested? Most of the testing is completed through CI, and the example module is locally compiled and tested in IDEA Additionally, there are some writing changes that are verified through demo code ### Was this patch authored or co-authored using generative AI tooling? no Closes apache#43526 from laglangyue/SPARK-45629. Lead-authored-by: tangjiafu <jiafu.tang@qq.com> Co-authored-by: tangjiafu <tangjiafu@corp.netease.com> Signed-off-by: yangjie01 <yangjie01@baidu.com> # Conflicts: # connector/connect/common/src/main/scala/org/apache/spark/sql/connect/client/GrpcExceptionConverter.scala # core/src/main/scala/org/apache/spark/storage/BlockManagerMasterEndpoint.scala # pom.xml # project/SparkBuild.scala # sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala # sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/OperatorStateMetadata.scala Revert "[SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES] Fix `Implicit definition should have explicit type`" This reverts commit bc67612. Fix Implicit definition should have explicit type fix install error add args for scala 2.13 fix args update pom java version update pom jvm target version fix implicit types rollback scala 2.13.8 rollback fmt blank space fix fix import fmt fmt not fail on violation

scabug added critical usability implicit labels Apr 7, 2017

scabug added this to the Backlog milestone Apr 7, 2017

scabug assigned retronym Apr 7, 2017

This was referenced Apr 7, 2017

better error message when implicits fail due to missing type ascription #5798

Closed

spurious warning on implicit definition being not applicable #7441

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Implicit *object* not found if it occurs later in same file #9674

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SethTisue removed the critical label Jul 27, 2017

scala deleted a comment from scabug Jul 19, 2022

SethTisue unassigned retronym Jul 19, 2022

SethTisue added help wanted good first issue labels Jul 19, 2022

som-snytt mentioned this issue Jul 20, 2022

Warn that implicit should have explicit type [ci: last-only] scala/scala#10083

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SethTisue added the has PR label Jul 20, 2022

SethTisue assigned som-snytt Jul 20, 2022

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lrytz closed this as completed in scala/scala#10083 Nov 29, 2022

SethTisue modified the milestones: Backlog, 2.13.11 Nov 29, 2022

laglangyue mentioned this issue Nov 30, 2023

[SPARK-45629][CORE][SQL][CONNECT][ML][STREAMING][BUILD][EXAMPLES]Fix Implicit definition should have explicit type apache/spark#43526

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warn on implicit def without explicit result type #5265

warn on implicit def without explicit result type #5265

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edited

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warn on implicit def without explicit result type #5265

warn on implicit def without explicit result type #5265

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