Replace silencer plugin with built-in warning configuration (#12543)

Since Scala 2.13.2, Scala introduced built-in support to
manage warnings in a more granular fashion, thus making
the silencer plugin we are currently using no longer
strictly useful. Removing compiler plugins also removes
friction from migrating to Scala 3 in the future. As a
cherry on top, the built-in warning configuration also
allows to check whether a `@nowarn` actually does
anything, allowing us to proactively remove unused
warnings should the need arise.

[Here][1] is s a blog post by the Scala team about it.

Warnings have been either solved or preserved if useful,
trying to minimize the scope (keeping it at the single
expression scope if possible). In particular, all
remaining usages of the Scala Collection API compatibility
module have been removed.

Using the silencer plugin also apparently hid a few
remaining usages of compatibility libraries that were used
as part of the transition from Scala 2.12 to Scala 2.13
that are no longer needed. Removing those warnings
highlighted those.

changelog_begin
changelog_end

[1]: https://www.scala-lang.org/2021/01/12/configuring-and-suppressing-warnings.html

bazel_tools/scala.bzl

@@ -39,28 +39,9 @@ def resolve_scala_deps(deps, scala_deps = [], versioned_deps = {}, versioned_sca
                         versioned_scala_deps.get(scala_major_version, [])
            ]
 
-def extra_scalacopts(scala_deps, plugins):
-    return (["-P:silencer:lineContentFilters=import scala.collection.compat._"] if (scala_major_version != "2.12" and
-                                                                                    silencer_plugin in plugins and
-                                                                                    "@maven//:org_scala_lang_modules_scala_collection_compat" in scala_deps) else [])
-
+# Please don't remove, this will be useful in the future to transition to Scala 3
 version_specific = {
-    "2.12": [
-        # these two flags turn on source-incompatible enhancements that are always
-        # on in Scala 2.13.  Despite the naming, though, the most impactful and
-        # 2.13-like change is -Ypartial-unification.  -Xsource:2.13 only turns on
-        # some minor, but in one specific case (scala/bug#10283) essential bug fixes
-        "-Xsource:2.13",
-        "-Ypartial-unification",
-        # adapted args is a deprecated feature:
-        # `def foo(a: (A, B))` can be called with `foo(a, b)`.
-        # properly it should be `foo((a,b))`
-        "-Yno-adapted-args",
-        "-Xlint:unsound-match",
-        "-Xlint:by-name-right-associative",  # will never be by-name if used correctly
-        "-Xfuture",
-        "-language:higherKinds",
-    ],
+    "2.13": [],
 }
 
 common_scalacopts = version_specific.get(scala_major_version, []) + [
@@ -96,8 +77,7 @@ common_scalacopts = version_specific.get(scala_major_version, []) + [
     # Gives a warning for functions declared as returning Unit, but the body returns a value
     "-Ywarn-value-discard",
     "-Ywarn-unused:imports",
-    # Allow `@nowarn` annotations that allegedly do nothing (necessary because of false positives)
-    "-Ywarn-unused:-nowarn",
+    "-Ywarn-unused:nowarn",
     "-Ywarn-unused",
 ]
 
@@ -109,12 +89,9 @@ common_plugins = [
     "@maven//:org_wartremover_wartremover_{}".format(scala_version_suffix),
 ]
 
+# Please don't remove, this will be useful in the future to transition to Scala 3
 version_specific_warts = {
-    "2.12": [
-        # On 2.13, this also triggers in string interpolation
-        # https://github.com/wartremover/wartremover/issues/447
-        "StringPlusAny",
-    ],
+    "2.13": [],
 }
 
 plugin_scalacopts = [
@@ -233,10 +210,9 @@ def _wrap_rule(
     exports = resolve_scala_deps(exports, scala_exports)
     if (len(exports) > 0):
         kwargs["exports"] = exports
-    compat_scalacopts = extra_scalacopts(scala_deps = scala_deps, plugins = plugins)
     rule(
         name = name,
-        scalacopts = common_scalacopts + plugin_scalacopts + compat_scalacopts + scalacopts,
+        scalacopts = common_scalacopts + plugin_scalacopts + scalacopts,
         plugins = common_plugins + plugins,
         deps = deps,
         runtime_deps = runtime_deps,
@@ -542,12 +518,11 @@ def _create_scaladoc_jar(
     # Limit execution to Linux and MacOS
     if is_windows == False:
         deps = resolve_scala_deps(deps, scala_deps, versioned_deps, versioned_scala_deps)
-        compat_scalacopts = extra_scalacopts(scala_deps = scala_deps, plugins = plugins)
         scaladoc_jar(
             name = name + "_scaladoc",
             deps = deps,
             srcs = srcs,
-            scalacopts = common_scalacopts + plugin_scalacopts + compat_scalacopts + scalacopts,
+            scalacopts = common_scalacopts + plugin_scalacopts + scalacopts,
             plugins = common_plugins + plugins,
             generated_srcs = generated_srcs,
             tags = ["scaladoc"],

compiler/scenario-service/server/BUILD.bazel

@@ -1,7 +1,7 @@
 # Copyright (c) 2022 Digital Asset (Switzerland) GmbH and/or its affiliates. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-load("//bazel_tools:scala.bzl", "da_scala_binary", "silencer_plugin")
+load("//bazel_tools:scala.bzl", "da_scala_binary")
 
 genrule(
     name = "scenario_service_jar",
@@ -15,12 +15,8 @@ da_scala_binary(
     name = "scenario-service-raw",
     srcs = glob(["src/main/scala/**/*.scala"]),
     main_class = "com.daml.lf.scenario.ScenarioServiceMain",
-    plugins = [
-        silencer_plugin,
-    ],
     resources = glob(["src/main/resources/*"]),
     scala_deps = [
-        "@maven//:org_scala_lang_modules_scala_collection_compat",
         "@maven//:com_typesafe_scala_logging_scala_logging",
         "@maven//:org_scalaz_scalaz_core",
         "@maven//:com_github_scopt_scopt",

compiler/scenario-service/server/src/main/scala/com/digitalasset/daml/lf/scenario/Context.scala

@@ -22,7 +22,6 @@ import com.daml.lf.engine.script.{Participants, Runner, Script, ScriptF, ScriptI
 
 import scala.concurrent.ExecutionContext
 import scala.concurrent.Future
-import scala.collection.compat._
 import scala.collection.immutable.HashMap
 import scala.util.{Failure, Success}
 

daml-lf/archive/BUILD.bazel

@@ -12,7 +12,6 @@ load(
     "da_scala_test_suite",
     "lf_scalacopts",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 load("//daml-lf/language:daml-lf.bzl", "LF_MAJOR_VERSIONS", "PROTO_LF_VERSIONS", "mangle_for_java", "versions")
 load(
@@ -96,12 +95,8 @@ da_haskell_library(
 da_scala_library(
     name = "daml_lf_archive_reader",
     srcs = glob(["src/main/scala/**/*.scala"]),
-    plugins = [
-        silencer_plugin,
-    ],
     scala_deps = [
         "@maven//:org_scalaz_scalaz_core",
-        "@maven//:org_scala_lang_modules_scala_collection_compat",
     ],
     scalacopts = lf_scalacopts_stricter,
     tags = ["maven_coordinates=com.daml:daml-lf-archive-reader:__VERSION__"],

daml-lf/archive/src/main/scala/com/digitalasset/daml/lf/archive/DecodeV1.scala

@@ -16,7 +16,6 @@ import com.daml.nameof.NameOf
 import com.daml.scalautil.Statement.discard
 
 import scala.Ordering.Implicits.infixOrderingOps
-import scala.collection.compat._
 import scala.collection.mutable
 import scala.jdk.CollectionConverters._
 

daml-lf/data/BUILD.bazel

@@ -8,7 +8,6 @@ load(
     "kind_projector_plugin",
     "lf_scalacopts",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 
 da_scala_library(
@@ -17,14 +16,11 @@ da_scala_library(
         glob(["src/main/scala/**/*.scala"]),
     plugins = [
         kind_projector_plugin,
-        silencer_plugin,
     ],
     scala_deps = [
         "@maven//:org_scalaz_scalaz_core",
     ],
-    scalacopts = lf_scalacopts_stricter + [
-        "-P:silencer:lineContentFilters=import ImmArraySeq.Implicits._",
-    ],
+    scalacopts = lf_scalacopts_stricter,
     tags = ["maven_coordinates=com.daml:daml-lf-data:__VERSION__"],
     visibility = [
         "//visibility:public",
@@ -41,20 +37,13 @@ da_scala_library(
 da_scala_test(
     name = "data-test",
     size = "small",
-    srcs = glob(["src/test/**/*.scala"]),
-    plugins = [
-        silencer_plugin,
-    ],
     scala_deps = [
         "@maven//:org_scalacheck_scalacheck",
         "@maven//:org_scalatestplus_scalacheck_1_15",
         "@maven//:org_scalaz_scalaz_core",
         "@maven//:org_scalaz_scalaz_scalacheck_binding",
     ],
-    scalacopts = lf_scalacopts + [
-        "-P:silencer:lineContentFilters=import ImmArraySeq.Implicits._",
-        "-P:silencer:lineContentFilters=signum",
-    ],
+    scalacopts = lf_scalacopts,
     deps = [
         ":data",
         "//daml-lf/data-scalacheck",

daml-lf/interface/BUILD.bazel

@@ -7,18 +7,13 @@ load(
     "da_scala_test",
     "lf_scalacopts",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 
 da_scala_library(
     name = "interface",
     srcs = glob(["src/main/**/*.scala"]),
-    plugins = [
-        silencer_plugin,
-    ],
     scala_deps = [
         "@maven//:org_scalaz_scalaz_core",
-        "@maven//:org_scala_lang_modules_scala_collection_compat",
     ],
     scalacopts = lf_scalacopts_stricter,
     tags = ["maven_coordinates=com.daml:daml-lf-interface:__VERSION__"],

daml-lf/interface/src/main/scala/com/digitalasset/daml/lf/iface/reader/Errors.scala

@@ -7,7 +7,6 @@ package reader
 import com.daml.lf.data.Ref.{DottedName, Name}
 
 import scala.language.implicitConversions
-import scala.collection.compat._
 import scala.collection.immutable.Map
 import scalaz.{-\/, ==>>, @@, Applicative, Cord, Monoid, Order, Semigroup, Tag, Traverse, \/, \/-}
 import scalaz.std.map._

daml-lf/language/BUILD.bazel

@@ -7,7 +7,6 @@ load(
     "da_scala_test",
     "lf_scalacopts",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 
 da_scala_library(
@@ -29,12 +28,7 @@ da_scala_test(
     name = "language-test",
     size = "small",
     srcs = glob(["src/test/**/*.scala"]),
-    plugins = [
-        silencer_plugin,
-    ],
-    scalacopts = lf_scalacopts + [
-        "-P:silencer:lineContentFilters=signum",
-    ],
+    scalacopts = lf_scalacopts,
     deps = [
         ":language",
         "//daml-lf/data",

daml-lf/language/src/test/scala/com/digitalasset/daml/lf/language/LanguageVersionSpec.scala

@@ -27,7 +27,7 @@ class LanguageVersionSpec extends AnyWordSpec with Matchers with TableDrivenProp
       forEvery(versions)(v2 =>
         LV.Ordering
           .compare(v1, v2)
-          .signum shouldBe (versionRank(v1) compareTo versionRank(v2)).signum
+          .sign shouldBe (versionRank(v1) compareTo versionRank(v2)).sign
       )
     )
   }

daml-lf/parser/BUILD.bazel

@@ -7,22 +7,16 @@ load(
     "da_scala_test",
     "lf_scalacopts",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 
 da_scala_library(
     name = "parser",
     srcs = glob(["src/main/**/*.scala"]),
-    plugins = [
-        silencer_plugin,
-    ],
     scala_deps = [
         "@maven//:org_scala_lang_modules_scala_parser_combinators",
         "@maven//:org_scalaz_scalaz_core",
     ],
-    scalacopts = lf_scalacopts_stricter + [
-        "-P:silencer:lineContentFilters=standardInterpolator",
-    ],
+    scalacopts = lf_scalacopts_stricter,
     visibility = [
         "//daml-lf:__subpackages__",
         "//ledger:__subpackages__",

daml-lf/parser/src/main/scala/com/digitalasset/daml/lf/testing/parser/Implicits.scala

@@ -31,11 +31,16 @@ object Implicits {
 
     @SuppressWarnings(Array("org.wartremover.warts.Any"))
     def n(args: Any*): Ref.Name =
-      Ref.Name.assertFromString(sc.standardInterpolator(identity, args.map(prettyPrint)))
+      Ref.Name.assertFromString(
+        StringContext.standardInterpolator(identity, args.map(prettyPrint), sc.parts)
+      )
 
     @SuppressWarnings(Array("org.wartremover.warts.Any"))
     private def interpolate[T](p: Parsers.Parser[T])(args: Seq[Any]): T =
-      Parsers.parseAll(Parsers.phrase(p), sc.standardInterpolator(identity, args.map(prettyPrint)))
+      Parsers.parseAll(
+        Parsers.phrase(p),
+        StringContext.standardInterpolator(identity, args.map(prettyPrint), sc.parts),
+      )
   }
 
   private def toString(x: BigDecimal) =

daml-lf/transaction-test-lib/BUILD.bazel

@@ -6,15 +6,13 @@ load(
     "da_scala_library",
     "kind_projector_plugin",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 
 da_scala_library(
     name = "transaction-test-lib",
     srcs = glob(["src/main/**/*.scala"]),
     plugins = [
         kind_projector_plugin,
-        silencer_plugin,
     ],
     scala_deps = [
         "@maven//:com_chuusai_shapeless",
@@ -23,11 +21,7 @@ da_scala_library(
         "@maven//:org_scalaz_scalaz_scalacheck_binding",
         "@maven//:org_scala_lang_modules_scala_collection_compat",
     ],
-    scalacopts = lf_scalacopts_stricter + [
-        "-P:silencer:lineContentFilters=import elt.injshrink",
-        # Forced upon us by Shrink
-        "-P:silencer:lineContentFilters=Stream.empty",
-    ],
+    scalacopts = lf_scalacopts_stricter,
     tags = ["maven_coordinates=com.daml:daml-lf-transaction-test-lib:__VERSION__"],
     visibility = ["//visibility:public"],
     deps = [

daml-lf/transaction-test-lib/src/main/scala/lf/value/test/TypedValueGenerators.scala

@@ -147,7 +147,6 @@ object TypedValueGenerators {
         Tag unsubst implicitly[Arbitrary[Vector[elt.Inj] @@ Div3]]
       }
       override def injshrink(implicit shr: Shrink[Value.ContractId]) = {
-        import elt.injshrink
         implicitly[Shrink[Vector[elt.Inj]]]
       }
     }
@@ -169,7 +168,6 @@ object TypedValueGenerators {
         implicitly[Arbitrary[Option[elt.Inj]]]
       }
       override def injshrink(implicit cid: Shrink[Value.ContractId]) = {
-        import elt.injshrink
         implicitly[Shrink[Option[elt.Inj]]]
       }
     }
@@ -306,7 +304,7 @@ object TypedValueGenerators {
           override def injshrink(implicit shr: Shrink[Value.ContractId]) =
             Shrink { ev =>
               if (!(values.headOption contains ev)) values.headOption.toStream
-              else Stream.empty
+              else Stream.empty: @annotation.nowarn("cat=deprecation")
             }
         },
       )

daml-lf/transaction/BUILD.bazel

@@ -8,7 +8,6 @@ load(
     "da_scala_test",
     "lf_scalacopts",
     "lf_scalacopts_stricter",
-    "silencer_plugin",
 )
 
 #
@@ -47,12 +46,8 @@ proto_jars(
 da_scala_library(
     name = "transaction",
     srcs = glob(["src/main/**/*.scala"]),
-    plugins = [
-        silencer_plugin,
-    ],
     scala_deps = [
         "@maven//:org_scalaz_scalaz_core",
-        "@maven//:org_scala_lang_modules_scala_collection_compat",
     ],
     scalacopts = lf_scalacopts_stricter,
     tags = ["maven_coordinates=com.daml:daml-lf-transaction:__VERSION__"],
@@ -77,16 +72,12 @@ da_scala_test(
         "src/test/**/value/*.scala",
         "src/test/**/transaction/*.scala",
     ]),
-    plugins = [
-        silencer_plugin,
-    ],
     scala_deps = [
         "@maven//:com_chuusai_shapeless",
         "@maven//:org_scalacheck_scalacheck",
         "@maven//:org_scalatestplus_scalacheck_1_15",
         "@maven//:org_scalaz_scalaz_core",
         "@maven//:org_scalaz_scalaz_scalacheck_binding",
-        "@maven//:org_scala_lang_modules_scala_collection_compat",
     ],
     scalacopts = lf_scalacopts,
     deps = [
@@ -107,9 +98,6 @@ da_scala_test(
     srcs = glob([
         "src/test/**/validation/*.scala",
     ]),
-    plugins = [
-        silencer_plugin,
-    ],
     scalacopts = lf_scalacopts,
     deps = [
         ":transaction",

daml-lf/transaction/src/main/scala/com/digitalasset/daml/lf/transaction/package.scala

@@ -3,7 +3,7 @@
 
 package com.daml.lf
 
-import scala.collection.compat._
+import scala.collection.BuildFrom
 
 package object transaction {