Add Function#signature for PostgreSQL function identity

lib/fx/adapters/postgres/functions.rb

@@ -12,7 +12,8 @@ class Functions
         FUNCTIONS_WITH_DEFINITIONS_QUERY = <<~SQL.freeze
           SELECT
               pp.proname AS name,
-              pg_get_functiondef(pp.oid) AS definition
+              pg_get_functiondef(pp.oid) AS definition,
+              pg_get_function_identity_arguments(pp.oid) AS arguments
           FROM pg_proc pp
           JOIN pg_namespace pn
               ON pn.oid = pp.pronamespace

lib/fx/function.rb

@@ -4,15 +4,27 @@ class Function
     include Comparable
 
     attr_reader :name, :definition
-    delegate :<=>, to: :name
 
     def initialize(row)
       @name = row.fetch("name")
       @definition = row.fetch("definition")
+      @arguments = row.fetch("arguments", nil)
+    end
+
+    def <=>(other)
+      signature <=> other.signature
     end
 
     def ==(other)
-      name == other.name && definition == other.definition
+      signature == other.signature && definition == other.definition
+    end
+
+    def signature
+      if @arguments.nil?
+        name
+      else
+        "#{name}(#{@arguments})"
+      end
     end
 
     def to_schema

spec/fx/function_spec.rb

@@ -2,44 +2,121 @@
 
 RSpec.describe Fx::Function do
   describe "#<=>" do
-    it "delegates to `name`" do
+    it "delegates to `signature`" do
       function_a = Fx::Function.new(
         "name" => "name_a",
-        "definition" => "some definition"
+        "definition" => "some definition",
+        "arguments" => ""
       )
       function_b = Fx::Function.new(
         "name" => "name_b",
-        "definition" => "some definition"
+        "definition" => "some definition",
+        "arguments" => ""
       )
       function_c = Fx::Function.new(
         "name" => "name_c",
-        "definition" => "some definition"
+        "definition" => "some definition",
+        "arguments" => ""
       )
 
       expect(function_b).to be_between(function_a, function_c)
     end
+
+    it "orders overloads by signature" do
+      add_int = Fx::Function.new(
+        "name" => "add",
+        "definition" => "some definition",
+        "arguments" => "integer, integer"
+      )
+      add_text = Fx::Function.new(
+        "name" => "add",
+        "definition" => "some definition",
+        "arguments" => "text, text"
+      )
+
+      expect(add_int <=> add_text).to be < 0
+    end
   end
 
   describe "#==" do
-    it "compares `name` and `definition`" do
+    it "compares `signature` and `definition`" do
       function_a = Fx::Function.new(
         "name" => "name_a",
-        "definition" => "some definition"
+        "definition" => "some definition",
+        "arguments" => ""
       )
       function_b = Fx::Function.new(
         "name" => "name_b",
-        "definition" => "some other definition"
+        "definition" => "some other definition",
+        "arguments" => ""
       )
 
       expect(function_a).not_to eq(function_b)
     end
+
+    it "distinguishes overloads with the same name" do
+      add_int = Fx::Function.new(
+        "name" => "add",
+        "definition" => "CREATE FUNCTION add(integer)",
+        "arguments" => "integer"
+      )
+      add_text = Fx::Function.new(
+        "name" => "add",
+        "definition" => "CREATE FUNCTION add(text)",
+        "arguments" => "text"
+      )
+
+      expect(add_int).not_to eq(add_text)
+    end
+  end
+
+  describe "#signature" do
+    it "returns name with arguments when arguments are present" do
+      function = Fx::Function.new(
+        "name" => "inc",
+        "definition" => "some definition",
+        "arguments" => "integer"
+      )
+
+      expect(function.signature).to eq("inc(integer)")
+    end
+
+    it "returns name with multiple arguments" do
+      function = Fx::Function.new(
+        "name" => "add",
+        "definition" => "some definition",
+        "arguments" => "integer, integer"
+      )
+
+      expect(function.signature).to eq("add(integer, integer)")
+    end
+
+    it "returns name with empty parens for no-arg functions" do
+      function = Fx::Function.new(
+        "name" => "now_utc",
+        "definition" => "some definition",
+        "arguments" => ""
+      )
+
+      expect(function.signature).to eq("now_utc()")
+    end
+
+    it "returns just the name when arguments key is missing" do
+      function = Fx::Function.new(
+        "name" => "now_utc",
+        "definition" => "some definition"
+      )
+
+      expect(function.signature).to eq("now_utc")
+    end
   end
 
   describe "#to_schema" do
     it "returns a schema compatible version of the function" do
       function = Fx::Function.new(
         "name" => "uppercase_users_name",
-        "definition" => "CREATE OR REPLACE TRIGGER uppercase_users_name ..."
+        "definition" => "CREATE OR REPLACE TRIGGER uppercase_users_name ...",
+        "arguments" => ""
       )
 
       expect(function.to_schema).to eq(<<-EOS)
@@ -52,7 +129,8 @@
     it "maintains backslashes" do
       function = Fx::Function.new(
         "name" => "regex",
-        "definition" => "CREATE OR REPLACE FUNCTION regex \\1"
+        "definition" => "CREATE OR REPLACE FUNCTION regex \\1",
+        "arguments" => ""
       )
 
       expect(function.to_schema).to eq(<<-'EOS')