feat: add base64 expression#4159
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Implement Spark base64 in Comet. Output is unchunked padded base64; the expression is marked Compatible only when chunkBase64=false (Spark 3.5+ with `spark.sql.chunkBase64String.enabled=false`), and Incompatible otherwise so users opt in via `spark.comet.expr.allowIncompatible=true`. Closes apache#419
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Which issue does this PR close?
Closes #419.
Rationale for this change
base64is a commonly used Spark string function. The expression coverage doc previously listed it as unsupported, so queries using it fell back to Spark.What changes are included in this PR?
spark_base64innative/spark-expr/src/string_funcs/base64.rsthat produces padded RFC 4648 base64 (no line breaks). Wired intocreate_comet_physical_funas"base64".spark/src/main/scala/org/apache/comet/serde/strings.scala:CometBase64for the Spark 3.4 case-class shape (Base64(child)). Always returnsIncompatiblebecause Spark 3.4 always chunks the output.CometBase64StaticInvokefor the Spark 3.5+ shape, whereBase64isRuntimeReplaceableand arrives asStaticInvoke(classOf[Base64], "encode", Seq(child, Literal(chunkBase64))). ReturnsCompatibleonly when the literalchunkBase64isfalse; otherwiseIncompatible.CometStaticInvokenow delegatesgetSupportLevelandgetExprConfigNameto its inner handler so theBase64-specific support level and config name (spark.comet.expr.Base64.allowIncompatible) take effect through the StaticInvoke dispatch path.spark/src/test/resources/sql-tests/expressions/string/base64.sqlcovers binary and string columns, literals, NULL, empty input, the SPARK-47307 58-byte chunking boundary, a 200-byte input, and the full 0x00..0xFF byte range.spark/src/test/resources/sql-tests/expressions/string/base64_chunked_fallback.sqlasserts that on Spark 3.5+ Comet falls back to Spark whenspark.sql.chunkBase64String.enabled=trueand incompatible expressions have not been opted in.docs/source/contributor-guide/spark_expressions_support.mdupdated with audit annotations for Spark 3.4.3 / 3.5.8 / 4.0.1.This change was scaffolded with the
implement-comet-expressionClaude skill and the resulting implementation was reviewed with theaudit-comet-expressionskill.How are these changes tested?
spark/src/test/resources/sql-tests/expressions/string/cover both the compatible (chunkBase64String.enabled=false) and the fallback (chunkBase64String.enabled=true) paths.native/spark-expr/src/string_funcs/base64.rscover array, scalar, NULL, and padding cases.make format,cargo clippy --all-targets --workspace -- -D warnings, and the targetedCometSqlFileTestSuiteruns all pass locally.