Implement lint command feature

src/cli.cr

@@ -25,6 +25,7 @@ module Mint
     register_sub_command docs, type: Docs
     register_sub_command loc, type: Loc
     register_sub_command ls, type: Ls
+    register_sub_command lint, type: Lint
 
     def run
       execute "Help" do

src/commands/lint.cr

@@ -0,0 +1,69 @@
+module Mint
+  class Cli < Admiral::Command
+    class Lint < Admiral::Command
+      include Command
+
+      define_help description: "Lints the project for syntax and type errors."
+
+      define_flag json : Bool,
+        description: "Output errors to a JSON file",
+        default: false,
+        required: false
+
+      def run
+        execute "Linting" do
+          lint
+        end
+      end
+
+      def lint
+        sources = [] of String
+        errors = [] of Exception
+
+        ast =
+          Ast.new
+            .merge(Core.ast)
+
+        begin
+          sources =
+            Dir.glob(SourceFiles.all)
+        rescue ex
+          errors << ex
+        end
+
+        sources.reduce(ast) do |memo, file|
+          begin
+            parsed =
+              Parser.parse(file)
+
+            memo.merge(parsed)
+          rescue ex
+            errors << ex
+          end
+          memo
+        end
+
+        if errors.empty?
+          type_checker =
+            TypeChecker.new(ast)
+
+          loop do
+            type_checker.check
+          rescue ex
+            errors << ex
+          else
+            break
+          end
+        end
+
+        if flags.json
+          puts errors.compact_map(&.message.presence).to_json
+        else
+          errors.each { |error| puts error }
+        end
+
+        exit(errors.empty? ? 0 : 1)
+      end
+    end
+  end
+end