Fix date_diff in Snowflake (#10672)

- Closes #10438
- The results are again aligned across backends.

distribution/lib/Standard/Snowflake/0.0.0-dev/src/Internal/Snowflake_Dialect.enso

@@ -628,16 +628,25 @@ make_date_diff arguments (metadata : Date_Period_Metadata) =
     if arguments.length != 2 then Error.throw (Illegal_State.Error "date_diff expects exactly 2 sub expressions. This is a bug in Database library.") else
         start = arguments.at 0
         end = arguments.at 1
-        part_with_multiplier = date_period_to_part_with_multiplier metadata.period
-        date_part = part_with_multiplier.first
-        multiplier = part_with_multiplier.second
-        ## The SQL type to add as a cast. This is needed, because otherwise this operation is losing type information,
-           especially if given NULL (Nothing). It would tell that it returns a VARCHAR which is not true.
-        sql_typ = sql_type_string_for_date_time metadata.input_value_type
-        diff = SQL_Builder.code "DATEDIFF('" ++ date_part ++ "', (" ++ start ++ ")::" ++ sql_typ ++ ", (" ++ end ++ ")::" ++ sql_typ ++ ")"
-        if multiplier == 1 then diff else
-            # We want to return integer, so we truncate any fractional part that did not constitute a full unit.
-            SQL_Builder.code "TRUNC(" ++ diff ++ " / " ++ multiplier.to_text ++ ")"
+        case metadata.period of
+            # Year / Quarter / Month rely on MONTHS_BETWEEN because DATEDIFF looked just at months and years and ignored days, yielding incorrect results.
+            Date_Period.Year ->
+                SQL_Builder.code "TRUNC(MONTHS_BETWEEN((" ++ end ++ ")::DATE, (" ++ start ++ ")::DATE) / 12)"
+            Date_Period.Quarter ->
+                SQL_Builder.code "TRUNC(MONTHS_BETWEEN((" ++ end ++ ")::DATE, (" ++ start ++ ")::DATE) / 3)"
+            Date_Period.Month ->
+                SQL_Builder.code "TRUNC(MONTHS_BETWEEN((" ++ end ++ ")::DATE, (" ++ start ++ ")::DATE))"
+            _ ->
+                part_with_multiplier = date_period_to_part_with_multiplier metadata.period
+                date_part = part_with_multiplier.first
+                multiplier = part_with_multiplier.second
+                ## The SQL type to add as a cast. This is needed, because otherwise this operation is losing type information,
+                   especially if given NULL (Nothing). It would tell that it returns a VARCHAR which is not true.
+                sql_typ = sql_type_string_for_date_time metadata.input_value_type
+                diff = SQL_Builder.code "DATEDIFF('" ++ date_part ++ "', (" ++ start ++ ")::" ++ sql_typ ++ ", (" ++ end ++ ")::" ++ sql_typ ++ ")"
+                if multiplier == 1 then diff else
+                    # We want to return integer, so we truncate any fractional part that did not constitute a full unit.
+                    SQL_Builder.code "TRUNC(" ++ diff ++ " / " ++ multiplier.to_text ++ ")"
 
 ## PRIVATE
 make_date_trunc_to_day arguments =

test/Snowflake_Tests/src/Snowflake_Spec.enso

@@ -600,8 +600,14 @@ with_secret name value callback = case value of
 get_configured_connection_details = Panic.rethrow <|
     account_name = Environment.get "ENSO_SNOWFLAKE_ACCOUNT"
     if account_name.is_nothing then Nothing else
+        if account_name.is_empty then
+            Panic.throw (Illegal_Argument.Error "ENSO_SNOWFLAKE_ACCOUNT is set, but empty. Please set all required environment variables.")
+
         get_var name =
-            Environment.get name if_missing=(Panic.throw (Illegal_State.Error "ENSO_SNOWFLAKE_ACCOUNT is set, but "+name+" is not. Please set all required environment variables."))
+            value = Environment.get name if_missing=(Panic.throw (Illegal_State.Error "ENSO_SNOWFLAKE_ACCOUNT is set, but "+name+" is not. Please set all required environment variables."))
+            if value.is_empty then
+                Panic.throw (Illegal_State.Error "The "+name+" environment variable is set, but it is empty. Please set all required environment variables.")
+            value
         user = get_var "ENSO_SNOWFLAKE_USER"
         password = get_var "ENSO_SNOWFLAKE_PASSWORD"
         database = get_var "ENSO_SNOWFLAKE_DATABASE"

test/Table_Tests/src/Common_Table_Operations/Date_Time_Spec.enso

@@ -303,9 +303,11 @@ add_specs suite_builder setup =
 
             (t1.at "X").date_diff (t1.at "Y") Date_Period.Month . to_vector . should_equal [1]
             (t1.at "X").date_diff (Date.new 2020 12 1) Date_Period.Month . to_vector . should_equal [-11]
+            (t1.at "X").date_diff (Date.new 2021 12 1) Date_Period.Month . to_vector . should_equal [0]
 
             (t1.at "X").date_diff (t1.at "Y") Date_Period.Quarter . to_vector . should_equal [0]
             (t1.at "X").date_diff (Date.new 2021 5 1) Date_Period.Quarter . to_vector . should_equal [-2]
+            (t1.at "X").date_diff (Date.new 2023 7 1) Date_Period.Quarter . to_vector . should_equal [6]
 
             (t1.at "X").date_diff (t1.at "Y") Date_Period.Year . to_vector . should_equal [0]
             (t1.at "X").date_diff (Date.new 2021 12 1) Date_Period.Year . to_vector . should_equal [0]
@@ -315,6 +317,7 @@ add_specs suite_builder setup =
             (t1.at "X1").date_diff (Date.new 2021 03 02) Date_Period.Day . to_vector . should_equal [59]
             (t1.at "X1").date_diff (Date.new 2021 03 02) Date_Period.Month . to_vector . should_equal [2]
             (t1.at "X1").date_diff (Date.new 2021 03 01) Date_Period.Day . to_vector . should_equal [58]
+            (t1.at "X1").date_diff (Date.new 2021 03 01) Date_Period.Month . to_vector . should_equal [1]
 
             # We do allow the `Time_Period.Day` as a kind of alias for `Date_Period.Day` here.
             (t1.at "X").date_diff (t1.at "Y") Time_Period.Day . to_vector . should_equal [32]
@@ -327,6 +330,7 @@ add_specs suite_builder setup =
             (t2.at "X").date_diff (Date_Time.new 2021 11 3 10 15 0 zone=zone) Date_Period.Day . to_vector . should_equal [0]
 
             (t2.at "X").date_diff (t2.at "Y") Date_Period.Month . to_vector . should_equal [1]
+            (t2.at "X").date_diff (Date_Time.new 2021 12 1 10 15 0 zone=zone) Date_Period.Month . to_vector . should_equal [0]
 
             (t2.at "X").date_diff (t2.at "Y") Date_Period.Year . to_vector . should_equal [0]
             (t2.at "X").date_diff (Date_Time.new 2031 12 1 10 15 0 zone=zone) Date_Period.Year . to_vector . should_equal [10]
@@ -387,19 +391,6 @@ add_specs suite_builder setup =
                     (t3.at "X").date_diff (t3.at "Y") Time_Period.Nanosecond . should_fail_with Unsupported_Database_Operation
                     (t3.at "X").date_diff (Time_Of_Day.new 10 15 12 34 56 78) Time_Period.Nanosecond . should_fail_with Unsupported_Database_Operation
 
-        ## TODO these were extracted from the test above, they may later be merged again, or we may keep them separate depending on resolution of
-           https://github.com/enso-org/enso/issues/10438
-        group_builder.specify "date_diff edge cases" pending=(if setup.prefix.contains "Snowflake" then "TODO: https://github.com/enso-org/enso/issues/10438") <|
-            t1 = dates1.get.select_columns ["d_X", "d_Y", "X1"] reorder=True . rename_columns ["X", "Y", "X1"]
-            ## TODO Snowflake just looks at year and month, but Postgres/in-memory look if it was a full month or not by looking at days
-            (t1.at "X").date_diff (Date.new 2021 12 1) Date_Period.Month . to_vector . should_equal [0]
-            (t1.at "X").date_diff (Date.new 2023 7 1) Date_Period.Quarter . to_vector . should_equal [6]
-
-            (t1.at "X1").date_diff (Date.new 2021 03 01) Date_Period.Month . to_vector . should_equal [1]
-
-            t2 = dates1.get.select_columns ["dt_X", "dt_Y"] reorder=True . rename_columns ["X", "Y"]
-            (t2.at "X").date_diff (Date_Time.new 2021 12 1 10 15 0 zone=zone) Date_Period.Month . to_vector . should_equal [0]
-
         group_builder.specify "date_diff should return integers" <|
             t = table_builder [["X", [Date.new 2021 01 31]], ["Y", [Time_Of_Day.new 12 30 20]], ["Z", [Date_Time.new 2021 12 5 12 30 20]]]
 

test/Table_Tests/src/Common_Table_Operations/Derived_Columns_Spec.enso

@@ -95,6 +95,7 @@ add_specs suite_builder setup =
             t2.set (Simple_Expression.Simple_Expr (Column_Ref.Name "C") (Simple_Calculation.Date_Add 5 Date_Period.Month)) "Z" . at "Z" . to_vector . should_equal [Date.new 2003 5 10, Date.new 2005 6 01]
             t2.set (Simple_Expression.Simple_Expr (Column_Ref.Name "D") (Simple_Calculation.Date_Add 15 Time_Period.Hour)) "Z" . at "Z" . to_vector . should_equal [Time_Of_Day.new 03 45, Time_Of_Day.new 16 01]
 
+            t2.set (Simple_Expression.Simple_Expr (Column_Ref.Name "C") (Simple_Calculation.Date_Diff (Date.new 2003 01 01) Date_Period.Year)) "Z" . at "Z" . to_vector . should_equal [0, -2]
             t2.set (Simple_Expression.Simple_Expr (Column_Ref.Name "D") (Simple_Calculation.Date_Diff (Time_Of_Day.new 13) Time_Period.Minute)) "Z" . at "Z" . to_vector . should_equal [15, 59+(60*11)]
 
             t2.set (Simple_Expression.Simple_Expr (Column_Ref.Name "C") (Simple_Calculation.Date_Part Date_Period.Year)) "Z" . at "Z" . to_vector . should_equal [2002, 2005]
@@ -106,10 +107,6 @@ add_specs suite_builder setup =
             t.set (Simple_Expression.Simple_Expr (Column_Ref.Name "x") (Simple_Calculation.Date_Part Date_Period.Year)) . should_fail_with Invalid_Value_Type
             Test.expect_panic Type_Error <| t2.set (Simple_Expression.Simple_Expr 42 (Simple_Calculation.Date_Diff "x" Date_Period.Year))
 
-        group_builder.specify "date/time (edge case)" pending=(pending_datetime.if_nothing (if setup.prefix.contains "Snowflake" then "TODO: https://github.com/enso-org/enso/issues/10438")) <|
-            t2 = table_builder [["C", [Date.new 2002 12 10, Date.new 2005 01 01]], ["D", [Time_Of_Day.new 12 45, Time_Of_Day.new 01 01]]]
-            t2.set (Simple_Expression.Simple_Expr (Column_Ref.Name "C") (Simple_Calculation.Date_Diff (Date.new 2003 01 01) Date_Period.Year)) "Z" . at "Z" . to_vector . should_equal [0, -2]
-
         group_builder.specify "boolean" <|
             t = table_builder [["A", [True, False]], ["T", [True, True]]]