From 6842afb345ee69aa6081e9764a087c164ba9402e Mon Sep 17 00:00:00 2001
From: Thibault Czarniak <thibault.czarniak@epfl.ch>
Date: Thu, 12 Sep 2024 17:30:37 +0200
Subject: [PATCH] Added ComparisonToEmptyList and ComparisonToEmptySet

---
 .../scala/fix/ComparisonToEmptyList.scala     | 26 ++++++++++++
 .../main/scala/fix/ComparisonToEmptySet.scala | 22 ++++++++++
 .../META-INF/services/scalafix.v1.Rule        |  4 +-
 .../scala/fix/ComparisonToEmptyList.scala     | 41 +++++++++++++++++++
 .../main/scala/fix/ComparisonToEmptySet.scala | 39 ++++++++++++++++++
 5 files changed, 131 insertions(+), 1 deletion(-)
 create mode 100644 input/src/main/scala/fix/ComparisonToEmptyList.scala
 create mode 100644 input/src/main/scala/fix/ComparisonToEmptySet.scala
 create mode 100644 rules/src/main/scala/fix/ComparisonToEmptyList.scala
 create mode 100644 rules/src/main/scala/fix/ComparisonToEmptySet.scala

diff --git a/input/src/main/scala/fix/ComparisonToEmptyList.scala b/input/src/main/scala/fix/ComparisonToEmptyList.scala
new file mode 100644
index 0000000..6735953
--- /dev/null
+++ b/input/src/main/scala/fix/ComparisonToEmptyList.scala
@@ -0,0 +1,26 @@
+/*
+rule = ComparisonToEmptyList
+ */
+package fix
+
+object ComparisonToEmptyList {
+  val a = List(1, 2, 3)
+
+  val b = a == List() // assert: ComparisonToEmptyList
+  val c = List() == a // assert: ComparisonToEmptyList
+
+  val d = a == List.empty // assert: ComparisonToEmptyList
+  val e = List.empty == a // assert: ComparisonToEmptyList
+
+  val f = a == Nil // assert: ComparisonToEmptyList
+  val g = Nil == a // assert: ComparisonToEmptyList
+
+  val h = List.apply() == a // assert: ComparisonToEmptyList
+  val i = a == List.apply() // assert: ComparisonToEmptyList
+
+  val j = a == List(3, 4) // scalafix: ok;
+  val k = List(3, 4) == a // scalafix: ok;
+  val l = a != List(3, 4) // scalafix: ok;
+  val m = List(3, 4) != a // scalafix: ok;
+
+}
diff --git a/input/src/main/scala/fix/ComparisonToEmptySet.scala b/input/src/main/scala/fix/ComparisonToEmptySet.scala
new file mode 100644
index 0000000..4bffdd8
--- /dev/null
+++ b/input/src/main/scala/fix/ComparisonToEmptySet.scala
@@ -0,0 +1,22 @@
+/*
+rule = ComparisonToEmptySet
+ */
+package fix
+
+object ComparisonToEmptySet {
+  val a = Set(1, 2, 3)
+
+  val b = a == Set() // assert: ComparisonToEmptySet
+  val c = Set() == a // assert: ComparisonToEmptySet
+
+  val d = a == Set.empty // assert: ComparisonToEmptySet
+  val e = Set.empty == a // assert: ComparisonToEmptySet
+
+  val h = Set.apply() == a // assert: ComparisonToEmptySet
+  val i = a == Set.apply() // assert: ComparisonToEmptySet
+
+  val j = a == Set(3, 4) // scalafix: ok;
+  val k = Set(3, 4) == a // scalafix: ok;
+  val l = a != Set(3, 4) // scalafix: ok;
+  val m = Set(3, 4) != a // scalafix: ok;
+}
diff --git a/rules/src/main/resources/META-INF/services/scalafix.v1.Rule b/rules/src/main/resources/META-INF/services/scalafix.v1.Rule
index deb8b6a..5ab490d 100644
--- a/rules/src/main/resources/META-INF/services/scalafix.v1.Rule
+++ b/rules/src/main/resources/META-INF/services/scalafix.v1.Rule
@@ -60,4 +60,6 @@ fix.BooleanParameter
 fix.BoundedByFinalType
 fix.BrokenOddness
 fix.ClassNames
-fix.CollectionNamingConfusion
\ No newline at end of file
+fix.CollectionNamingConfusion
+fix.ComparisonToEmptyList
+fix.ComparisonToEmptySet
\ No newline at end of file
diff --git a/rules/src/main/scala/fix/ComparisonToEmptyList.scala b/rules/src/main/scala/fix/ComparisonToEmptyList.scala
new file mode 100644
index 0000000..1333f5e
--- /dev/null
+++ b/rules/src/main/scala/fix/ComparisonToEmptyList.scala
@@ -0,0 +1,41 @@
+/*
+rule = ComparisonToEmptyList
+ */
+package fix
+
+import scalafix.lint.LintSeverity
+import scalafix.v1._
+
+import scala.meta._
+
+class ComparisonToEmptyList extends SemanticRule("ComparisonToEmptyList") {
+
+  private def diag(pos: Position) = Diagnostic(
+    "",
+    "Checks for code like `a == List()`, `a == Nil`, `a != List()` or `a != Nil`.",
+    pos,
+    "Prefer use of `isEmpty`, or `nonEmpty` instead of comparison to an empty List.",
+    LintSeverity.Info
+  )
+
+  override def fix(implicit doc: SemanticDocument): Patch = {
+
+    def isEmptyList(term: Term) = term match {
+      // List()
+      case Term.Apply.After_4_6_0(Term.Name("List"), Term.ArgClause(Nil, _)) => true
+      // List.apply()
+      case Term.Apply.After_4_6_0(Term.Select(Term.Name("List"), Term.Name("apply")), Term.ArgClause(Nil, _)) => true
+      // List.empty
+      case Term.Select(Term.Name("List"), Term.Name("empty")) => true
+      // Nil
+      case Term.Name("Nil") => true
+      case _                => false
+    }
+
+    doc.tree.collect {
+      // Corresponds to a == List() or List() == a, or any of the empty lists above. Also handles a != List() or List() != a, with the empty lists above too.
+      case Term.ApplyInfix.After_4_6_0(lhs, Term.Name("==" | "!="), _, Term.ArgClause(List(rhs), _)) if isEmptyList(lhs) || isEmptyList(rhs) => Patch.lint(diag(lhs.pos))
+    }.asPatch
+  }
+
+}
diff --git a/rules/src/main/scala/fix/ComparisonToEmptySet.scala b/rules/src/main/scala/fix/ComparisonToEmptySet.scala
new file mode 100644
index 0000000..b612361
--- /dev/null
+++ b/rules/src/main/scala/fix/ComparisonToEmptySet.scala
@@ -0,0 +1,39 @@
+/*
+rule = ComparisonToEmptySet
+ */
+package fix
+
+import scalafix.lint.LintSeverity
+import scalafix.v1._
+
+import scala.meta._
+
+class ComparisonToEmptySet extends SemanticRule("ComparisonToEmptySet") {
+
+  private def diag(pos: Position) = Diagnostic(
+    "",
+    "Checks for code like `a == Set()` or `a == Set.empty`.",
+    pos,
+    "Prefer use of `isEmpty` instead of comparison to an empty Set.",
+    LintSeverity.Info
+  )
+
+  override def fix(implicit doc: SemanticDocument): Patch = {
+
+    def isEmptySet(term: Term) = term match {
+      // Set()
+      case Term.Apply.After_4_6_0(Term.Name("Set"), Term.ArgClause(Nil, _)) => true
+      // Set.apply()
+      case Term.Apply.After_4_6_0(Term.Select(Term.Name("Set"), Term.Name("apply")), Term.ArgClause(Nil, _)) => true
+      // Set.empty
+      case Term.Select(Term.Name("Set"), Term.Name("empty")) => true
+      case _                                                 => false
+    }
+
+    doc.tree.collect {
+      // Corresponds to a == Set() or Set() == a, or any of the empty sets above. Also handles a != Set() or Set() != a, with the empty sets above too.
+      case Term.ApplyInfix.After_4_6_0(lhs, Term.Name("==" | "!="), _, Term.ArgClause(List(rhs), _)) if isEmptySet(lhs) || isEmptySet(rhs) => Patch.lint(diag(lhs.pos))
+    }.asPatch
+  }
+
+}