Conditionally add !lib to default globs

spec/ameba/config_spec.cr

@@ -9,10 +9,20 @@ module Ameba
     end
 
     describe ".new" do
-      it "loads default globs when config is empty" do
-        yml = YAML.parse "{}"
-        config = Config.new(yml)
-        config.globs.should eq Config::DEFAULT_GLOBS
+      context "when config is empty" do
+        it "loads default globs" do
+          yml = YAML.parse "{}"
+          config = Config.new(yml)
+          config.globs.should eq ["**/*.cr"]
+        end
+
+        it "only sets !lib as a default glob when there are .cr files in lib" do
+          File.touch "lib/shard.cr"
+          yml = YAML.parse "{}"
+          config = Config.new(yml)
+          config.globs.should eq Config::DEFAULT_GLOBS
+          File.delete "lib/shard.cr"
+        end
       end
 
       it "initializes globs as string" do
@@ -102,7 +112,7 @@ module Ameba
       config = Config.load config_sample
 
       it "holds source globs" do
-        config.globs.should eq Config::DEFAULT_GLOBS
+        config.globs.should eq ["**/*.cr"]
       end
 
       it "allows to set globs" do

src/ameba/config.cr

@@ -95,7 +95,7 @@ class Ameba::Config
     @rules = Rule.rules.map &.new(config).as(Rule::Base)
     @rule_groups = @rules.group_by &.group
     @excluded = load_array_section(config, "Excluded")
-    @globs = load_array_section(config, "Globs", DEFAULT_GLOBS)
+    @globs = load_array_section(config, "Globs", default_globs)
 
     return unless formatter_name = load_formatter_name(config)
     self.formatter = formatter_name
@@ -239,6 +239,13 @@ class Ameba::Config
     end
   end
 
+  private def default_globs
+    DEFAULT_GLOBS.select do |glob|
+      !Dir[glob].empty? ||
+        (glob.starts_with?("!") && !Dir["#{glob[1..-1]}/**/*.cr"].empty?)
+    end
+  end
+
   # :nodoc:
   module RuleConfig
     # Define rule properties

src/ameba/glob_utils.cr

@@ -21,9 +21,8 @@ module Ameba
     # ```
     def expand(globs)
       globs.flat_map do |glob|
-        raise ArgumentError.new("No files found matching #{glob}") if Dir[glob].empty?
-
         glob += "/**/*.cr" if File.directory?(glob)
+        raise ArgumentError.new("No files found matching #{glob}") if Dir[glob].empty?
         Dir[glob]
       end.uniq!
     end