fix: type the NULL that a date shifted by NULL compiles to

pkg-py/src/commons/_definitions/_emit_sql.py

@@ -43,6 +43,8 @@
     "weeks": "604800000000",
 }
 
+_NULL_DATETIME = {"snowflake": "TIMESTAMP_TZ", "databricks": "TIMESTAMP"}
+
 _SIMPLE_FUNCTIONS = {
     "length": "length",
     "lower": "lower",
@@ -424,11 +426,15 @@ def _temporal_shift(node: Ir, state: _State, selected: str | None) -> str | None
     interval becomes a count of microseconds.
     """
     attrs = node.attrs
+    dialect = state.dialect
+    # The checker accepts an untyped NULL as the interval, which shifts to
+    # NULL. Neither warehouse adds a bare NULL to a date, so it is typed.
+    if node.type == "datetime" and "null" in (attrs["lhs"].kind, attrs["rhs"].kind):
+        return f"CAST(NULL AS {_NULL_DATETIME[dialect]})"
     lhs_interval = attrs["lhs"].type == "interval"
     rhs_interval = attrs["rhs"].type == "interval"
     if not lhs_interval and not rhs_interval:
         return None
-    dialect = state.dialect
     if lhs_interval and attrs["op"] == "-":
         _unsupported(
             dialect,

pkg-r/NEWS.md

@@ -1,5 +1,7 @@
 # commons (development version)
 
+* A definition that adds `NULL` to a date, such as `created + NULL`, now compiles to SQL that Snowflake accepts. It compiles to a typed `NULL` timestamp (#441).
+
 * A definition that divides by a compound expression, such as `amount / (ratio * 2)`, now compiles to the correct Snowflake and Databricks SQL. The parentheses around the divisor were dropped, so the query divided by `ratio` alone (#439).
 
 * `commons()` gains a `mode` argument. With `mode = "trusted only"`, the agent answers only with trusted calculations. It never writes its own SQL or R, and it tells the user when no trusted calculation answers a question. These answers carry no provenance markers.

pkg-r/R/definition-emit-sql.R

@@ -582,6 +582,17 @@ definition_sql_similar <- function(node, state, dialect, selected) {
 }
 
 definition_sql_temporal_shift <- function(node, state, dialect, selected) {
+  # The checker accepts an untyped NULL as the interval, which shifts to
+  # NULL. Neither warehouse adds a bare NULL to a date, so it is typed.
+  if (
+    identical(node$type, "datetime") &&
+      "null" %in% c(node$lhs$kind, node$rhs$kind)
+  ) {
+    return(sprintf(
+      "CAST(NULL AS %s)",
+      definition_sql_null_datetime[[dialect]]
+    ))
+  }
   lhs_interval <- identical(node$lhs$type, "interval")
   rhs_interval <- identical(node$rhs$type, "interval")
   if (!lhs_interval && !rhs_interval) {
@@ -775,6 +786,11 @@ definition_sql_abort_unsupported <- function(dialect, what, why) {
   )
 }
 
+definition_sql_null_datetime <- list(
+  snowflake = "TIMESTAMP_TZ",
+  databricks = "TIMESTAMP"
+)
+
 definition_sql_nan_note <- list(
   snowflake = paste(
     "Snowflake orders a NaN as equal to itself and greater than every number,",

pkg-r/tests/testthat/fixtures/shared/definition-warehouse-sql.json

@@ -73,6 +73,10 @@
       "survey::dynamic match": {
         "SQL(snowflake)": { "notes_contain": ["newline characters"] }
       },
+      "survey::nullable date shift": {
+        "SQL(snowflake)": { "code": "CAST(NULL AS TIMESTAMP_TZ)" },
+        "SQL(databricks)": { "code": "CAST(NULL AS TIMESTAMP)" }
+      },
       "survey::negative quotient": {
         "SQL(snowflake)": {
           "code_contains": [

tests/shared/definition-warehouse-sql.json

@@ -73,6 +73,10 @@
       "survey::dynamic match": {
         "SQL(snowflake)": { "notes_contain": ["newline characters"] }
       },
+      "survey::nullable date shift": {
+        "SQL(snowflake)": { "code": "CAST(NULL AS TIMESTAMP_TZ)" },
+        "SQL(databricks)": { "code": "CAST(NULL AS TIMESTAMP)" }
+      },
       "survey::negative quotient": {
         "SQL(snowflake)": {
           "code_contains": [