feat: Implement map-to-string casting#4647
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
andygrove
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getChan
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Jun 14, 2026
| query expect_fallback(Cast from MapType) | ||
| -- Empty map: still falls back because planning sees `map()` as `Map<NullType, NullType>`, | ||
| -- which reaches the existing NullType -> StringType cast fallback. | ||
| query expect_fallback(Cast from NullType to StringType is not supported) |
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not sure if this is the intended behavior. How should we handle the empty map(Map<NullType, NullType) case?
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Which issue does this PR close?
Closes #4631.
Rationale for this change
Comet should render Spark map-to-string casts natively for non-empty maps, matching Spark's
{k -> v, ...}formatting. Emptymap()still falls back because Catalyst types it asMap<NullType, NullType>; no special-case handling is added here, so once null casting is supported this path should work naturally.What changes are included in this PR?
native/spark-expr.CometCastsupport checks so non-empty maps can execute natively.cast_complex_types_to_string.sql, while keeping empty map fallback.implement-comet-expressionworkflow to scaffold the implementation.How are these changes tested?
PROFILES='-Pspark-4.0' make format./mvnw test -Dsuites="org.apache.comet.CometSqlFileTestSuite cast_complex_types_to_string" -Dtest=none