From dc6d9bc93011b90691ffb692b3c894eba766847e Mon Sep 17 00:00:00 2001
From: Rob Howard <rob@robhoward.id.au>
Date: Tue, 31 Oct 2017 10:51:20 +1100
Subject: [PATCH] Adds a "starts with prop_ but is not a Property" warning.

---
 src/Jack/Runner.js   | 38 +++++++++++++++++++++-----------------
 src/Jack/Runner.purs | 26 ++++++++++++++++++++++++--
 test/Foo.purs        |  4 ++++
 3 files changed, 49 insertions(+), 19 deletions(-)

diff --git a/src/Jack/Runner.js b/src/Jack/Runner.js
index ec3a775..ffd03b1 100644
--- a/src/Jack/Runner.js
+++ b/src/Jack/Runner.js
@@ -1,29 +1,33 @@
 "use strict";
 
 exports.findProperties = function (module) {
-  return function () {
-    var properties = {};
-    var exports = require(module);
+  return function (tuple) {
+    return function () {
+      var properties = {};
+      var badPropertyNames = [];
+      var exports = require(module);
 
-    for (var name in exports) {
-      if (name.startsWith("prop_")) {
-        var property = exports[name];
+      for (var name in exports) {
+        if (name.startsWith("prop_")) {
+          var property = exports[name];
 
-        if (typeof property !== "object") {
-          // not an object, so not a property test
-          continue;
-        }
+          if (typeof property !== "object") {
+            // not an object, so not a property test
+            badPropertyNames.push(name);
+            continue;
+          }
 
-        if (!property.hasOwnProperty("Property :: Gen Result")) {
-          // 'Property :: Gen Result' field was missing, so not a property test
-          continue;
-        }
+          if (!property.hasOwnProperty("Property :: Gen Result")) {
+            // 'Property :: Gen Result' field was missing, so not a property test
+            continue;
+          }
 
-        properties[name] = property;
+          properties[name] = property;
+        }
       }
-    }
 
-    return properties;
+      return tuple(badPropertyNames)(properties);
+    };
   };
 };
 
diff --git a/src/Jack/Runner.purs b/src/Jack/Runner.purs
index 396001e..6fefda4 100644
--- a/src/Jack/Runner.purs
+++ b/src/Jack/Runner.purs
@@ -4,10 +4,12 @@ module Jack.Runner (
   , checkModules
   ) where
 
+import Data.Traversable (for)
 import Control.Monad.Eff (Eff)
 import Control.Monad.Eff.Console (CONSOLE, log)
 import Control.Monad.Eff.Random (RANDOM)
 
+import Data.Tuple.Nested (type (/\), (/\))
 import Data.StrMap (StrMap)
 import Data.StrMap as StrMap
 import Data.Array as Array
@@ -24,13 +26,29 @@ jackMain modules = do
 checkModule :: forall e. String -> Eff ("random" :: RANDOM, "console" :: CONSOLE | e) Boolean
 checkModule moduleName = do
   let
+    rat ns = do
+      log ""
+      log "*** Warning ***"
+      _ <- for ns $ \n -> do
+        log $ "- " <> n <> " starts with prop_ but is not of type Property"
+      log ""
+      log "  You may be trying to define something like:"
+      log "    prop_example :: Int -> Property"
+      log ""
+      log "  Jack doesn't have Arbitrary like QuickCheck, and so cannot automatically provide"
+      log "  property inputs in the same way; it uses forAll instead."
+      log "  See https://github.com/jystic/purescript-jack#getting-started for some property"
+      log "  examples to get started with."
+      log ""
     pyjamas b1 name prop = do
       log $ "=== " <> name <> " from " <> moduleName <> " ==="
       b2 <- check prop
       log $ ""
       pure $ b1 && b2
 
-  props <- findProperties moduleName
+  (badPropNames /\ props) <- findProperties moduleName (/\)
+
+  when (not <<< Array.null $ badPropNames) $ rat badPropNames
   StrMap.foldM pyjamas true props
 
 checkModules :: forall e. Array String -> Eff ("random" :: RANDOM, "console" :: CONSOLE | e) Boolean
@@ -41,6 +59,10 @@ checkModules modules =
   in
     Array.foldM loop true modules
 
-foreign import findProperties :: forall e. String -> Eff e (StrMap Property)
+foreign import findProperties ::
+  forall e a b.
+  String ->
+  (a -> b -> a /\ b) ->
+  Eff e (Array String /\ StrMap Property)
 
 foreign import exit :: forall e. Int -> Eff e Unit
diff --git a/test/Foo.purs b/test/Foo.purs
index 287adb0..f4db5a0 100644
--- a/test/Foo.purs
+++ b/test/Foo.purs
@@ -102,3 +102,7 @@ prop_even_strings_end_with_evens =
         property false
       Just x ->
         property $ elem x evens
+
+prop_bad :: Int -> Property
+prop_bad n =
+  property $ elem n [1,2,3]