[AURON #1863] Support native Flink UNIX_TIMESTAMP: converter integration (#2448)

# Which issue does this PR close?

Part of #1863. Not `Closes`, because the issue description also covers
the 0-input form, which this PR does not implement.

This is the Flink Java side of `UNIX_TIMESTAMP`. The native function it
calls merged in #2409. Together they cover the 1-input and 2-input forms
from the issue description.

The 0-input form is still outstanding. It is a different function rather
than a missing branch: Flink binds the niladic form to
`DateTimeUtils.unixTimestamp()`, which reads the clock per record and
parses nothing, so it needs its own design pass. The converter rejects
it explicitly and falls back to Flink's engine, and #1863 stays open to
track it.

# Rationale for this change

This completes native support for Flink's `UNIX_TIMESTAMP` by wiring the
Flink Calc converter to emit the native function added in #2409. Without
it the native function is unreachable, and any Calc containing
`UNIX_TIMESTAMP` falls back to Flink's engine for the whole Calc.

# What changes are included in this PR?

The converter recognizes `UNIX_TIMESTAMP` and lowers the 1-argument and
2-argument forms to the native `Flink_UnixTimestamp` node.

`UNIX_TIMESTAMP` resolves to `SqlKind.OTHER_FUNCTION`, so it is matched
by reference identity on the operator before the supported-kinds switch,
the same way `TRY_CAST` is handled.

A format scanner translates the supported subset of Java date-format
letters (`yyyy MM dd HH mm ss` and literals) to the native format.
Anything outside that subset falls back: other pattern letters,
unsupported run-lengths, a non-literal format argument, the 0-argument
form, and a numeric field adjacent to another numeric field where the
run-length would not survive translation (for example `yyyyMd`). Falling
back keeps results correct rather than risking a silent divergence.

The session time zone is resolved at plan time and passed into the node.
This required completing the config threading in the standalone-Calc
path, which passed a persisted config that does not carry
`table.local-time-zone`. That gap had no effect until now:
`UNIX_TIMESTAMP` is the first time-zone-sensitive expression the
converter supports, and the earlier ones (arithmetic, comparison,
logical, cast) never read the session zone. The effective node config is
threaded through instead, so the configured zone reaches the native
evaluation.

# Are there any user-facing changes?

Yes. `UNIX_TIMESTAMP(string)` and `UNIX_TIMESTAMP(string, format)` now
execute on the native engine when the format is a supported literal
pattern. Unsupported patterns and the 0-argument form continue to run on
Flink's engine, with the same results as before.

# How was this patch tested?

Unit tests for the scanner (accept/reject, quote escaping, the adjacency
rule), the converter (node shape, format translation, time-zone
propagation), and the operator-identity invariant. Fallback tests assert
that unsupported inputs actually fall back rather than silently
producing a native plan.

An end-to-end ITCase runs `UNIX_TIMESTAMP(ts)` with a non-UTC session
zone and confirms the native result matches the expected epoch values.
The executed native plan shows the function and the resolved zone,
confirming the query runs natively rather than falling back.

160 tests pass in `auron-flink-planner` on the rebased branch, with
spotless clean and 0 checkstyle violations.

# Was this patch authored or co-authored using generative AI tooling?
- [x] Yes
- [ ] No

Generated-by: Claude Code (Claude Opus 5)

Author: weiqingy

auron-flink-extension/auron-flink-planner/src/main/java/org/apache/auron/flink/table/planner/converter/FlinkDateTimeFormatConverter.java

@@ -0,0 +1,234 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.auron.flink.table.planner.converter;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Translates a {@code java.text.SimpleDateFormat} pattern into the native parser's
+ * {@code strftime}-style format string, or reports that the pattern cannot be translated.
+ *
+ * <p>The native {@code Flink_UnixTimestamp} function replicates {@code SimpleDateFormat} lenient
+ * parsing only for a fixed set of numeric fields. This converter is the plan-time gate: it accepts
+ * a pattern only when every token maps to a field the native parser handles identically, and
+ * returns {@link Optional#empty()} otherwise so the whole {@code Calc} falls back to Flink's engine.
+ *
+ * <p>Accepted fields and their native specifiers:
+ * <ul>
+ *   <li>{@code yyy} / {@code yyyy} &rarr; {@code %Y} (year)
+ *   <li>{@code M} / {@code MM} &rarr; {@code %m} (month)
+ *   <li>{@code d} / {@code dd} &rarr; {@code %d} (day of month)
+ *   <li>{@code H} / {@code HH} &rarr; {@code %H} (hour of day)
+ *   <li>{@code m} / {@code mm} &rarr; {@code %M} (minute)
+ *   <li>{@code s} / {@code ss} &rarr; {@code %S} (second)
+ * </ul>
+ *
+ * <p>Non-alphabetic characters are literals (a literal {@code %} is emitted as {@code %%}).
+ * {@code SimpleDateFormat} single-quote escaping applies, including the doubled {@code ''} that
+ * denotes a literal quote. Every other ASCII letter and every unlisted run length forces a fall
+ * back, because Java reserves all letters and the omitted forms either depend on a locale or on the
+ * clock at parse time.
+ *
+ * <p>Adjacency rule: run length is erased by the translation ({@code M} and {@code MM} both become
+ * {@code %m}), yet the native parser reads each numeric field at a canonical width (year 4; month,
+ * day, hour, minute, second 2) while Java's lenient scan window equals the run length. When two
+ * numeric fields are adjacent with no literal separator, those two widths must agree, so the left
+ * field's run length must equal its canonical width; otherwise the pattern falls back to avoid a
+ * silent divergence (e.g. {@code yyyyMd} on {@code 20201010} yields month 1 in Java but month 10
+ * natively).
+ */
+public final class FlinkDateTimeFormatConverter {
+
+    private FlinkDateTimeFormatConverter() {
+        // utility class
+    }
+
+    /**
+     * Translates the given Java {@code SimpleDateFormat} pattern to the native {@code strftime}-style
+     * format string.
+     *
+     * @param javaPattern the Java date-time format pattern, never {@code null}. Null is rejected
+     *     rather than reported as untranslatable: {@link Optional#empty()} means the user wrote a
+     *     pattern outside the native surface and the {@code Calc} should fall back, whereas a null
+     *     pattern means the caller never resolved one, which is a plumbing bug that a silent
+     *     fallback would hide.
+     * @return the translated native format string, or {@link Optional#empty()} if any part of the
+     *     pattern is outside the natively supported surface
+     * @throws NullPointerException if {@code javaPattern} is null
+     */
+    public static Optional<String> translate(String javaPattern) {
+        Objects.requireNonNull(javaPattern, "format pattern must not be null");
+        List<Token> tokens = scan(javaPattern);
+        if (tokens == null) {
+            return Optional.empty();
+        }
+        if (!adjacencyValid(tokens)) {
+            return Optional.empty();
+        }
+        StringBuilder out = new StringBuilder();
+        for (Token token : tokens) {
+            out.append(token.rendered);
+        }
+        return Optional.of(out.toString());
+    }
+
+    /**
+     * Walks the pattern into a token list, accumulating literal runs and emitting one token per
+     * pattern-letter field. Returns {@code null} on any unsupported letter, unsupported run length,
+     * or unterminated quote.
+     */
+    private static List<Token> scan(String pattern) {
+        List<Token> tokens = new ArrayList<>();
+        StringBuilder literal = new StringBuilder();
+        int i = 0;
+        int n = pattern.length();
+        while (i < n) {
+            char c = pattern.charAt(i);
+            if (c == '\'') {
+                if (i + 1 < n && pattern.charAt(i + 1) == '\'') {
+                    literal.append('\'');
+                    i += 2;
+                    continue;
+                }
+                i++;
+                boolean closed = false;
+                while (i < n) {
+                    char q = pattern.charAt(i);
+                    if (q == '\'') {
+                        if (i + 1 < n && pattern.charAt(i + 1) == '\'') {
+                            literal.append('\'');
+                            i += 2;
+                            continue;
+                        }
+                        closed = true;
+                        i++;
+                        break;
+                    }
+                    literal.append(q);
+                    i++;
+                }
+                if (!closed) {
+                    return null;
+                }
+            } else if (isAsciiLetter(c)) {
+                int j = i;
+                while (j < n && pattern.charAt(j) == c) {
+                    j++;
+                }
+                Field field = fieldFor(c, j - i);
+                if (field == null) {
+                    return null;
+                }
+                flushLiteral(tokens, literal);
+                tokens.add(Token.field(field, j - i));
+                i = j;
+            } else {
+                literal.append(c);
+                i++;
+            }
+        }
+        flushLiteral(tokens, literal);
+        return tokens;
+    }
+
+    private static void flushLiteral(List<Token> tokens, StringBuilder literal) {
+        if (literal.length() > 0) {
+            tokens.add(Token.literal(literal.toString()));
+            literal.setLength(0);
+        }
+    }
+
+    /**
+     * Checks the adjacency rule over the token list: for every field immediately followed by another
+     * field (no intervening literal), the left field's run length must equal its canonical width.
+     */
+    private static boolean adjacencyValid(List<Token> tokens) {
+        for (int i = 0; i + 1 < tokens.size(); i++) {
+            Token left = tokens.get(i);
+            Token right = tokens.get(i + 1);
+            if (left.field != null && right.field != null && left.runLength != left.field.canonicalWidth) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static boolean isAsciiLetter(char c) {
+        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
+    }
+
+    private static Field fieldFor(char letter, int runLength) {
+        switch (letter) {
+            case 'y':
+                return runLength == 3 || runLength == 4 ? Field.YEAR : null;
+            case 'M':
+                return runLength == 1 || runLength == 2 ? Field.MONTH : null;
+            case 'd':
+                return runLength == 1 || runLength == 2 ? Field.DAY : null;
+            case 'H':
+                return runLength == 1 || runLength == 2 ? Field.HOUR : null;
+            case 'm':
+                return runLength == 1 || runLength == 2 ? Field.MINUTE : null;
+            case 's':
+                return runLength == 1 || runLength == 2 ? Field.SECOND : null;
+            default:
+                return null;
+        }
+    }
+
+    /** A supported numeric field: its native specifier and the width the native parser reads. */
+    private enum Field {
+        YEAR("%Y", 4),
+        MONTH("%m", 2),
+        DAY("%d", 2),
+        HOUR("%H", 2),
+        MINUTE("%M", 2),
+        SECOND("%S", 2);
+
+        private final String specifier;
+        private final int canonicalWidth;
+
+        Field(String specifier, int canonicalWidth) {
+            this.specifier = specifier;
+            this.canonicalWidth = canonicalWidth;
+        }
+    }
+
+    /** A scanned token: either a field (non-null {@link #field}) or a literal run. */
+    private static final class Token {
+        private final Field field;
+        private final int runLength;
+        private final String rendered;
+
+        private Token(Field field, int runLength, String rendered) {
+            this.field = field;
+            this.runLength = runLength;
+            this.rendered = rendered;
+        }
+
+        static Token field(Field field, int runLength) {
+            return new Token(field, runLength, field.specifier);
+        }
+
+        static Token literal(String raw) {
+            return new Token(null, 0, raw.replace("%", "%%"));
+        }
+    }
+}

auron-flink-extension/auron-flink-planner/src/main/java/org/apache/auron/flink/table/planner/converter/FlinkNodeConverterUtils.java

@@ -16,10 +16,14 @@
  */
 package org.apache.auron.flink.table.planner.converter;
 
+import java.util.List;
 import org.apache.auron.flink.utils.SchemaConverters;
+import org.apache.auron.protobuf.ArrowType;
 import org.apache.auron.protobuf.PhysicalCastNode;
 import org.apache.auron.protobuf.PhysicalExprNode;
+import org.apache.auron.protobuf.PhysicalScalarFunctionNode;
 import org.apache.auron.protobuf.PhysicalTryCastNode;
+import org.apache.auron.protobuf.ScalarFunction;
 import org.apache.calcite.rel.type.RelDataType;
 import org.apache.calcite.rel.type.RelDataTypeFactory;
 import org.apache.calcite.rel.type.RelDataTypeSystem;
@@ -140,6 +144,27 @@ public static PhysicalExprNode wrapInCast(PhysicalExprNode expr, RelDataType tar
                 .build();
     }
 
+    /**
+     * Assembles a {@link PhysicalScalarFunctionNode} that routes to Auron's ext-function registry
+     * ({@link ScalarFunction#AuronExtFunctions}) by name. The arguments must already be converted to
+     * native expression nodes.
+     *
+     * @param name the registry name of the ext function (e.g. {@code "Flink_UnixTimestamp"})
+     * @param args the already-converted argument expressions, in call order
+     * @param returnType the native Arrow return type of the function
+     * @return a {@link PhysicalExprNode} wrapping the scalar-function call
+     */
+    public static PhysicalExprNode buildExtScalarFunctionNode(
+            String name, List<PhysicalExprNode> args, ArrowType returnType) {
+        return PhysicalExprNode.newBuilder()
+                .setScalarFunction(PhysicalScalarFunctionNode.newBuilder()
+                        .setName(name)
+                        .setFun(ScalarFunction.AuronExtFunctions)
+                        .addAllArgs(args)
+                        .setReturnType(returnType))
+                .build();
+    }
+
     private static boolean notApproxType(SqlTypeName typeName) {
         return typeName != SqlTypeName.FLOAT && typeName != SqlTypeName.DOUBLE;
     }