From 3f50f78ebaccdf02e2f08c7ee12d5594f9b2ac44 Mon Sep 17 00:00:00 2001
From: Brendan Hansknecht <brendan.hansknecht@gmail.com>
Date: Sun, 3 Dec 2023 18:39:02 -0800
Subject: [PATCH] update tests and Dict.keepShared semantics

---
 crates/compiler/builtins/roc/Dict.roc    | 24 ++++++++++++++----------
 crates/compiler/test_gen/src/gen_dict.rs |  6 +++---
 crates/compiler/test_gen/src/gen_set.rs  |  2 +-
 3 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/crates/compiler/builtins/roc/Dict.roc b/crates/compiler/builtins/roc/Dict.roc
index d48118d12d..84285d7fc8 100644
--- a/crates/compiler/builtins/roc/Dict.roc
+++ b/crates/compiler/builtins/roc/Dict.roc
@@ -629,23 +629,26 @@ insertAll = \xs, ys ->
 
 ## Combine two dictionaries by keeping the [intersection](https://en.wikipedia.org/wiki/Intersection_(set_theory))
 ## of all the key-value pairs. This means that we keep only those pairs
-## that are in both dictionaries. Note that where there are pairs with
-## the same key, the value contained in the first input will be retained,
-## and the value in the second input will be removed.
+## that are in both dictionaries. Both the key and value must match to be kept.
 ## ```
 ## first =
 ##     Dict.single 1 "Keep Me"
 ##     |> Dict.insert 2 "And Me"
+##     |> Dict.insert 3 "Not this one"
 ##
 ## second =
 ##     Dict.single 1 "Keep Me"
 ##     |> Dict.insert 2 "And Me"
-##     |> Dict.insert 3 "But Not Me"
+##     |> Dict.insert 3 "This has a different value"
 ##     |> Dict.insert 4 "Or Me"
 ##
-## expect Dict.keepShared first second == first
+## expected =
+##     Dict.single 1 "Keep Me"
+##     |> Dict.insert 2 "And Me"
+##
+## expect Dict.keepShared first second == expected
 ## ```
-keepShared : Dict k v, Dict k v -> Dict k v where k implements Hash & Eq
+keepShared : Dict k v, Dict k v -> Dict k v where k implements Hash & Eq, v implements Eq
 keepShared = \xs, ys ->
     if len ys < len xs then
         keepShared ys xs
@@ -654,10 +657,11 @@ keepShared = \xs, ys ->
             xs
             (withCapacity (len xs))
             (\state, k, v ->
-                if contains ys k then
-                    insert state k v
-                else
-                    state
+                when get ys k is
+                    Ok yv if v == yv ->
+                        insert state k v
+                    _ ->
+                        state
             )
 
 ## Remove the key-value pairs in the first input that are also in the second
diff --git a/crates/compiler/test_gen/src/gen_dict.rs b/crates/compiler/test_gen/src/gen_dict.rs
index 6e0181223c..a82a803b96 100644
--- a/crates/compiler/test_gen/src/gen_dict.rs
+++ b/crates/compiler/test_gen/src/gen_dict.rs
@@ -436,7 +436,7 @@ fn keep_shared() {
 
 #[test]
 #[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
-fn keep_shared_prefer_first() {
+fn keep_shared_value_must_match() {
     assert_evals_to!(
         indoc!(
             r#"
@@ -453,14 +453,14 @@ fn keep_shared_prefer_first() {
             dict2 =
                 Dict.empty {}
                     |> Dict.insert 0 100
-                    |> Dict.insert 2 200
+                    |> Dict.insert 2 2
                     |> Dict.insert 4 300
 
             Dict.keepShared dict1 dict2
                 |> Dict.values
             "#
         ),
-        RocList::from_slice(&[2, 4]),
+        RocList::from_slice(&[2]),
         RocList<i64>
     );
 }
diff --git a/crates/compiler/test_gen/src/gen_set.rs b/crates/compiler/test_gen/src/gen_set.rs
index e046899e0f..75201c38a4 100644
--- a/crates/compiler/test_gen/src/gen_set.rs
+++ b/crates/compiler/test_gen/src/gen_set.rs
@@ -120,7 +120,7 @@ fn union() {
                 |> Set.toList
             "#
         ),
-        RocList::from_slice(&[1, 2, 3, 4]),
+        RocList::from_slice(&[1, 3, 4, 2]),
         RocList<i64>
     );
 }