Remove support for ===, =~, and !~ operators in Lint/UnusedComp…

…arison

These comparison operators can have side-effects depending on the obj/args,
so there's no way to know if these are unused without semantic analysis.

spec/ameba/rule/lint/unused_comparison_spec.cr

@@ -37,13 +37,12 @@ module Ameba::Rule::Lint
         CRYSTAL
     end
 
-    it "passes if a regex literal is part of a comparison" do
+    it "passes for unused comparisons with `===`, `=~`, and `!~`" do
       expect_no_issues subject, <<-CRYSTAL
-        /f(o+)(bar?)/ === "fooba"
-        puts $~
-        "foobar" =~ /(o+)ba(r?)/
-        puts $1
-      CRYSTAL
+        /foo(bar)?/ =~ baz
+        "foobar" !~ /(o+)ba(r?)/
+        "hello" === world
+        CRYSTAL
     end
 
     it "fails for all comparison operators" do
@@ -52,12 +51,6 @@ module Ameba::Rule::Lint
         # ^^^^^^ error: Comparison operation is unused
           x != 2
         # ^^^^^^ error: Comparison operation is unused
-          x =~ 2
-        # ^^^^^^ error: Comparison operation is unused
-          x !~ 2
-        # ^^^^^^ error: Comparison operation is unused
-          x === 2
-        # ^^^^^^^ error: Comparison operation is unused
           x < 2
         # ^^^^^ error: Comparison operation is unused
           x <= 2

src/ameba/rule/lint/unused_comparison.cr

@@ -42,20 +42,14 @@ module Ameba::Rule::Lint
 
     MSG = "Comparison operation is unused"
 
-    COMPARISON_OPERATORS = %w[
-      == != =~ !~ ===
-      < <= > >= <=>
-    ]
+    COMPARISON_OPERATORS = %w[== != < <= > >= <=>]
 
     def test(source : Source)
       AST::ImplicitReturnVisitor.new(self, source)
     end
 
     def test(source, node : Crystal::Call, last_is_used : Bool)
       if !last_is_used && node.name.in?(COMPARISON_OPERATORS) && node.args.size == 1
-        return if node.obj.is_a?(Crystal::RegexLiteral) ||
-                  node.args.first.is_a?(Crystal::RegexLiteral)
-
         issue_for node, MSG
       end
     end