Merge pull request #302 from 'BetterErrors/feature/hints'

After some refactoring.

Author: RobinDaugherty

lib/better_errors/error_page.rb

@@ -67,6 +67,10 @@ def exception_message
       exception.message.strip.gsub(/(\r?\n\s*\r?\n)+/, "\n")
     end
 
+    def exception_hint
+      exception.hint
+    end
+
     def active_support_actions
       return [] unless defined?(ActiveSupport::ActionableError)
 

lib/better_errors/exception_hint.rb

@@ -0,0 +1,29 @@
+module BetterErrors
+  class ExceptionHint
+    def initialize(exception)
+      @exception = exception
+    end
+
+    def hint
+      case exception
+      when NoMethodError
+        /\Aundefined method `(?<method>[^']+)' for (?<val>[^:]+):(?<klass>\w+)/.match(exception.message) do |match|
+          if match[:val] == "nil"
+            return "Something is `nil` when it probably shouldn't be."
+          elsif !match[:klass].start_with? '0x'
+            return "`#{match[:method]}` is being called on a `#{match[:klass]}` object, "\
+              "which might not be the type of object you were expecting."
+          end
+        end
+      when NameError
+        /\Aundefined local variable or method `(?<method>[^']+)' for/.match(exception.message) do |match|
+          return "`#{match[:method]}` is probably misspelled."
+        end
+      end
+    end
+
+    private
+
+    attr_reader :exception
+  end
+end

lib/better_errors/raised_exception.rb

@@ -1,7 +1,9 @@
+require 'better_errors/exception_hint'
+
 # @private
 module BetterErrors
   class RaisedException
-    attr_reader :exception, :message, :backtrace
+    attr_reader :exception, :message, :backtrace, :hint
 
     def initialize(exception)
       if exception.class.name == "ActionView::Template::Error" && exception.respond_to?(:cause)
@@ -23,6 +25,7 @@ def initialize(exception)
       @message = exception.message
 
       setup_backtrace
+      setup_hint
       massage_syntax_error
     end
 
@@ -78,5 +81,9 @@ def massage_syntax_error
         end
       end
     end
+
+    def setup_hint
+      @hint = ExceptionHint.new(exception).hint
+    end
   end
 end

lib/better_errors/templates/main.erb

@@ -90,7 +90,7 @@
         nav.sidebar,
         .frame_info {
             position: fixed;
-            top: 95px;
+            top: 102px;
             bottom: 0;
 
             box-sizing: border-box;
@@ -102,7 +102,7 @@
         nav.sidebar {
             width: 40%;
             left: 20px;
-            top: 115px;
+            top: 122px;
             bottom: 20px;
         }
 
@@ -131,7 +131,7 @@
     header.exception {
         padding: 18px 20px;
 
-        height: 59px;
+        height: 66px;
         min-height: 59px;
 
         overflow: hidden;
@@ -764,6 +764,9 @@
                     <% end %>
                 </div>
             <% end %>
+            <% if exception_hint %>
+              <h2>Hint: <%= exception_hint %></h2>
+            <% end %>
         </header>
     </div>
 

spec/better_errors/exception_hint_spec.rb

@@ -0,0 +1,53 @@
+require 'spec_helper'
+
+RSpec.describe BetterErrors::ExceptionHint do
+  let(:described_instance) { described_class.new(exception) }
+
+  describe '#hint' do
+    subject(:hint) { described_instance.hint }
+
+    context "when the exception is a NameError" do
+      let(:exception) {
+        begin
+          foo
+        rescue NameError => e
+          e
+        end
+      }
+
+      it { is_expected.to eq("`foo` is probably misspelled.") }
+    end
+
+    context "when the exception is a NoMethodError" do
+      let(:exception) {
+        begin
+          val.foo
+        rescue NoMethodError => e
+          e
+        end
+      }
+
+      context "on `nil`" do
+        let(:val) { nil }
+
+        it { is_expected.to eq("Something is `nil` when it probably shouldn't be.") }
+      end
+
+      context 'on an unnamed object type' do
+        let(:val) { Class.new }
+
+        it { is_expected.to be_nil }
+      end
+
+      context "on other values" do
+        let(:val) { 42 }
+
+        it {
+          is_expected.to match(
+            /`foo` is being called on a `(Integer|Fixnum)` object, which might not be the type of object you were expecting./
+          )
+        }
+      end
+    end
+  end
+end

spec/better_errors/raised_exception_spec.rb

@@ -4,7 +4,12 @@
 module BetterErrors
   describe RaisedException do
     let(:exception) { RuntimeError.new("whoops") }
-    subject { RaisedException.new(exception) }
+    subject(:described_instance) { RaisedException.new(exception) }
+
+    before do
+      allow(BetterErrors::ExceptionHint).to receive(:new).and_return(exception_hint)
+    end
+    let(:exception_hint) { instance_double(BetterErrors::ExceptionHint, hint: nil) }
 
     its(:exception) { is_expected.to eq exception }
     its(:message)   { is_expected.to eq "whoops" }
@@ -103,5 +108,22 @@ def cause
         expect(subject.backtrace.first.line).to eq(11)
       end
     end
+
+    describe '#hint' do
+      subject(:hint) { described_instance.hint }
+
+      it 'uses ExceptionHint to get a hint for the exception' do
+        hint
+        expect(BetterErrors::ExceptionHint).to have_received(:new).with(exception)
+      end
+
+      context "when ExceptionHint returns a string" do
+        let(:exception_hint) { instance_double(BetterErrors::ExceptionHint, hint: "Hint text") }
+
+        it 'returns the value from ExceptionHint' do
+          expect(hint).to eq("Hint text")
+        end
+      end
+    end
   end
 end