Raise error for bad paths

Before:

If the path referenced a missing value in the input, treat it as a nil.

After:

If the path references a missing value in the input, raise an error.
This makes it necessary to catch errors and ensure that the context
is marked appropriately.

Since a path lookup is so stringent, introduce the presence_check.

lib/floe.rb

@@ -43,6 +43,7 @@ module Floe
   class Error < StandardError; end
   class InvalidWorkflowError < Error; end
   class InvalidExecutionInput < Error; end
+  class PathError < Error; end
 
   def self.logger
     @logger ||= NullLogger.new

lib/floe/workflow/choice_rule/data.rb

@@ -5,14 +5,13 @@ class Workflow
     class ChoiceRule
       class Data < Floe::Workflow::ChoiceRule
         def true?(context, input)
+          return presence_check(context, input) if compare_key == "IsPresent"
+
           lhs = variable_value(context, input)
           rhs = compare_value(context, input)
 
-          validate!(lhs)
-
           case compare_key
           when "IsNull" then is_null?(lhs)
-          when "IsPresent" then is_present?(lhs)
           when "IsNumeric" then is_numeric?(lhs)
           when "IsString" then is_string?(lhs)
           when "IsBoolean" then is_boolean?(lhs)
@@ -47,16 +46,31 @@ def true?(context, input)
 
         private
 
-        def validate!(value)
-          raise "No such variable [#{variable}]" if value.nil? && !%w[IsNull IsPresent].include?(compare_key)
+        def presence_check(context, input)
+          # Get the right hand side for {"Variable": "$.foo", "IsPresent": true} i.e.: true
+          # If true  then return true when present.
+          # If false then return true when not present.
+          rhs = compare_value(context, input)
+          # Don't need the variable_value, just need to see if the path finds the value.
+          variable_value(context, input)
+
+          # The variable_value is present
+          # If rhs is true, then presence check was successful, return true.
+          rhs
+        rescue Floe::PathError
+          # variable_value is not present. (the path lookup threw an error)
+          # If rhs is false, then it successfully wasn't present, return true.
+          !rhs
         end
 
         def is_null?(value) # rubocop:disable Naming/PredicateName
           value.nil?
         end
 
-        def is_present?(value) # rubocop:disable Naming/PredicateName
-          !value.nil?
+        # If it got here (and value was fetched), then it is present.
+        # This probably will never be called, but keeping just in case.
+        def is_present?(_value) # rubocop:disable Naming/PredicateName
+          true
         end
 
         def is_numeric?(value) # rubocop:disable Naming/PredicateName

lib/floe/workflow/path.rb

@@ -34,7 +34,18 @@ def value(context, input = {})
         return obj if path == "$"
 
         results = JsonPath.on(obj, path)
-        results.count < 2 ? results.first : results
+        case results.count
+        when 0
+          raise Floe::PathError, "Path [#{payload}] references an invalid value"
+        when 1
+          results.first
+        else
+          results
+        end
+      end
+
+      def to_s
+        payload
       end
     end
   end

spec/workflow/choice_rule_spec.rb

@@ -93,7 +93,7 @@
         let(:input) { {} }
 
         it "raises an exception" do
-          expect { subject }.to raise_exception(RuntimeError, "No such variable [$.foo]")
+          expect { subject }.to raise_exception(Floe::PathError, "Path [$.foo] references an invalid value")
         end
       end
 
@@ -118,22 +118,51 @@
       end
 
       context "with IsPresent" do
-        let(:payload) { {"Variable" => "$.foo", "IsPresent" => true, "Next" => "FirstMatchState"} }
+        let(:positive) { true }
+        let(:payload) { {"Variable" => "$.foo", "IsPresent" => positive, "Next" => "FirstMatchState"} }
 
         context "with null" do
           let(:input) { {"foo" => nil} }
+          it { expect(subject).to eq(true) }
+        end
 
-          it "returns false" do
-            expect(subject).to eq(false)
-          end
+        context "with false" do
+          let(:input) { {"foo" => "bar"} }
+          it { expect(subject).to eq(true) }
         end
 
-        context "with non-null" do
+        context "with string" do
+          let(:input) { {"foo" => false} }
+          it { expect(subject).to eq(true) }
+        end
+
+        context "with missing value" do
+          let(:input) { {} }
+          it { expect(subject).to eq(false) }
+        end
+
+        context "with null" do
+          let(:positive) { false }
+          let(:input) { {"foo" => nil} }
+          it { expect(subject).to eq(false) }
+        end
+
+        context "with false" do
+          let(:positive) { false }
           let(:input) { {"foo" => "bar"} }
+          it { expect(subject).to eq(false) }
+        end
 
-          it "returns true" do
-            expect(subject).to eq(true)
-          end
+        context "with string" do
+          let(:positive) { false }
+          let(:input) { {"foo" => false} }
+          it { expect(subject).to eq(false) }
+        end
+
+        context "with missing value" do
+          let(:positive) { false }
+          let(:input) { {} }
+          it { expect(subject).to eq(true) }
         end
       end
 
@@ -279,6 +308,11 @@
             expect(subject).to eq(false)
           end
         end
+
+        context "with path not found" do
+          let(:input) { {"foo" => 2} }
+          it { expect { subject }.to raise_error(Floe::PathError, "Path [$.bar] references an invalid value") }
+        end
       end
 
       context "with a NumericLessThan" do

spec/workflow/intrinsic_function_spec.rb

@@ -655,8 +655,8 @@
       end
 
       it "handles invalid path references" do
-        result = described_class.value("States.Array($.xxx)", {"context" => {"baz" => "qux"}}, {"input" => {"foo" => "bar"}})
-        expect(result).to eq([nil])
+        ctx = {"context" => {"baz" => "qux"}}, {"input" => {"foo" => "bar"}}
+        expect { described_class.value("States.Array($.xxx)", ctx) }.to raise_error(Floe::PathError, "Path [$.xxx] references an invalid value")
       end
     end
 

spec/workflow/path_spec.rb

@@ -11,15 +11,15 @@
   describe "#value" do
     context "referencing the global context" do
       it "with a missing value" do
-        expect(described_class.new("$$.foo").value({})).to be_nil
+        expect { described_class.new("$$.foo").value({}, {"foo" => "bar"}) }.to raise_error(Floe::PathError, "Path [$$.foo] references an invalid value")
       end
 
       it "with a single value" do
-        expect(described_class.new("$$.foo").value({"foo" => "bar"})).to eq("bar")
+        expect(described_class.new("$$.foo").value({"foo" => "bar"}, {})).to eq("bar")
       end
 
       it "with a nested hash" do
-        expect(described_class.new("$$.foo.bar").value({"foo" => {"bar" => "baz"}})).to eq("baz")
+        expect(described_class.new("$$.foo.bar").value({"foo" => {"bar" => "baz"}}, {})).to eq("baz")
       end
 
       it "with an array" do
@@ -33,7 +33,7 @@
 
     context "referencing the inputs" do
       it "with a missing value" do
-        expect(described_class.new("$.foo").value({"foo" => "bar"})).to be_nil
+        expect { described_class.new("$.foo").value({"foo" => "bar"}, {}) }.to raise_error(Floe::PathError, "Path [$.foo] references an invalid value")
       end
 
       it "with a single value" do

spec/workflow/states/choice_spec.rb

@@ -49,8 +49,14 @@
 
   describe "#run_nonblock!" do
     context "with a missing variable" do
-      it "raises an exception" do
-        expect { state.run_nonblock!(ctx) }.to raise_error(RuntimeError, "No such variable [$.foo]")
+      it "shows error" do
+        workflow.run_nonblock
+        expect(ctx.output).to eq(
+          {
+            "Cause" => "Path [$.foo] references an invalid value",
+            "Error" => "States.Runtime"
+          }
+        )
       end
     end
 

spec/workflow/states/pass_spec.rb

@@ -86,6 +86,34 @@
 
     #   it { expect { workflow }.to raise_error(Floe::InvalidWorkflowError, "States.PassState error") }
     # end
+
+    context "With an invalid InputPath" do
+      let(:payload) do
+        {
+          "PassState" => {
+            "Type"      => "Pass",
+            "InputPath" => "bad",
+            "End"       => true
+          }
+        }
+      end
+
+      it { expect { workflow }.to raise_error(Floe::InvalidWorkflowError, "Path [bad] must start with \"$\"") }
+    end
+
+    context "With an invalid OutputPath" do
+      let(:payload) do
+        {
+          "PassState" => {
+            "Type"       => "Pass",
+            "OutputPath" => "bad",
+            "End"        => true
+          }
+        }
+      end
+
+      it { expect { workflow }.to raise_error(Floe::InvalidWorkflowError, "Path [bad] must start with \"$\"") }
+    end
   end
 
   describe "#end?" do
@@ -124,6 +152,52 @@
       end
     end
 
+    context "With a missing InputPath" do
+      let(:payload) do
+        {
+          "PassState" => {
+            "Type"      => "Pass",
+            "End"       => true,
+            "InputPath" => "$.missing"
+          }
+        }
+      end
+
+      it "completes with an error" do
+        workflow.run_nonblock
+        expect(ctx.state_finished?).to eq(true)
+        expect(ctx.output).to eq(
+          {
+            "Cause" => "Path [$.missing] references an invalid value",
+            "Error" => "States.Runtime"
+          }
+        )
+      end
+    end
+
+    context "With a missing OutputPath" do
+      let(:payload) do
+        {
+          "PassState" => {
+            "Type"       => "Pass",
+            "End"        => true,
+            "OutputPath" => "$.missing.spot"
+          }
+        }
+      end
+
+      it "completes with an error" do
+        workflow.run_nonblock
+        expect(ctx.state_finished?).to eq(true)
+        expect(ctx.output).to eq(
+          {
+            "Cause" => "Path [$.missing.spot] references an invalid value",
+            "Error" => "States.Runtime"
+          }
+        )
+      end
+    end
+
     # https://states-language.net/#inputoutput-processing-examples
     context "with 2 blocks" do
       let(:payload) do
@@ -182,6 +256,18 @@
         end
       end
 
+      context "with Invalid InputPath" do
+        let(:input) { {} }
+        let(:payload) do
+          {"Pass" => {"Type" => "Pass", "End" => true, "InputPath" => "$.color"}}
+        end
+
+        it "detects missing value" do
+          workflow.run_nonblock
+          expect(ctx.output).to eq({"Cause" => "Path [$.color] references an invalid value", "Error" => "States.Runtime"})
+        end
+      end
+
       context "with OutputPath" do
         let(:input)   { {"color" => "red", "garbage" => nil} }
         let(:payload) { {"Pass" => {"Type" => "Pass", "End" => true, "OutputPath" => "$.color"}} }