Merge pull request #2136 from GiganticMinecraft/scalafix_lint

build.sbt

@@ -15,6 +15,8 @@ ThisBuild / description := "ギガンティック☆整地鯖の独自要素を
 // Scalafixが要求するため、semanticdbは有効化する
 ThisBuild / semanticdbEnabled := true
 ThisBuild / semanticdbVersion := scalafixSemanticdb.revision
+ThisBuild / scalafixScalaBinaryVersion :=
+  CrossVersion.binaryScalaVersion(scalaVersion.value)
 
 // endregion
 
@@ -68,6 +70,9 @@ val providedDependencies = Seq(
   "org.typelevel" %% "simulacrum" % "1.0.1"
 ).map(_ % "provided")
 
+val scalafixCoreDep =
+  "ch.epfl.scala" %% "scalafix-core" % _root_.scalafix.sbt.BuildInfo.scalafixVersion % ScalafixConfig
+
 val testDependencies = Seq(
   "org.scalamock" %% "scalamock" % "5.2.0",
   "org.scalatest" %% "scalatest" % "3.2.16",
@@ -189,7 +194,7 @@ Compile / PB.targets := Seq(scalapb.gen() -> (Compile / sourceManaged).value / "
 lazy val root = (project in file(".")).settings(
   name := "SeichiAssist",
   assembly / assemblyOutputPath := baseDirectory.value / "target" / "build" / "SeichiAssist.jar",
-  libraryDependencies := providedDependencies ++ testDependencies ++ dependenciesToEmbed,
+  libraryDependencies := (providedDependencies :+ scalafixCoreDep) ++ testDependencies ++ dependenciesToEmbed,
   excludeDependencies := Seq(ExclusionRule(organization = "org.bukkit", name = "bukkit")),
   unmanagedBase := baseDirectory.value / "localDependencies",
   scalacOptions ++= Seq(

src/scalafix/scala/fix/WarnUnoverriddenImplicitToStringCallsOnCaseClass.scala

@@ -0,0 +1,58 @@
+package fix
+
+import scalafix.v1._
+
+import scala.meta._
+
+/**
+ * Lints on string interpolation where its variable part contains `case class` without `toString`.
+ */
+// noinspection ScalaUnusedSymbol; referred from scalafix implicitly
+// NOTE: see AST on https://xuwei-k.github.io/scalameta-ast/ or https://astexplorer.net
+class WarnUnoverriddenImplicitToStringCallsOnCaseClass extends SemanticRule("WarnUnoverriddenImplicitToStringCallsOnCaseClass") {
+  override def fix(implicit doc: SemanticDocument): Patch = {
+    val s = doc.tree.collect {
+      // string interpolation in standard library
+      case Term.Interpolate((prefix, _, args)) =>
+        if (prefix.value != "s") {
+          return Patch.empty
+        }
+
+        Patch.fromIterable(
+          args.collect { arg =>
+            val tp = arg.symbol
+            val info = tp.info.get
+            // does `tp` point to some `case class`?
+            val isCaseClass = info.isCase && info.isClass
+
+            // lazily evaluated since most classes are not `case class`
+            lazy val isToStringOverriden = info.overriddenSymbols.exists(overridenMethodSym => overridenMethodSym.value == "toString" && {
+              overridenMethodSym.info.get.signature match {
+                // def toString[](): <return type> の形の override を見つけたい。
+                // もし toString() の return type が String のサブタイプにならないような型であれば
+                // scalafix が走る前にコンパイルが落ちるので、ここで改めて return type が
+                // String のサブタイプであるかは考慮する必要はない
+                case MethodSignature(List(), List(), _) => true
+                case _ => false
+              }
+            })
+
+            if (!isCaseClass || isToStringOverriden) {
+              return Patch.empty
+            }
+
+            Patch.lint(new Diagnostic {
+              override def message: String = "Case class value shouldn't be interpolated, use `toString` " +
+                "if you wish to interpolate the String representation into the string"
+
+              // points to arg
+              override def position: _root_.scala.meta.Position = arg.pos
+            })
+          }
+        )
+      case _ => Patch.empty
+    }
+
+    Patch.fromIterable(s)
+  }
+}