ESQL: Fix function registry concurrency issues on constructor (#123492)

Fixes #123430

There were 2 problems here:
- We were filling a static field (used to auto-cast string literals) within a constructor, which is also called in multiple places
- The field was only filled with non-snapshot functions, so snapshot function auto-casting wasn't possible

Fixed both bugs by making the field non-static instead, and a fix to use the snapshot registry (if available) in the string casting rule.

Author: ivancea

docs/changelog/123492.yaml

@@ -0,0 +1,6 @@
+pr: 123492
+summary: Fix function registry concurrency issues on constructor
+area: ES|QL
+type: bug
+issues:
+ - 123430

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/analysis/Analyzer.java

@@ -1187,7 +1187,7 @@ private static class ImplicitCasting extends ParameterizedRule<LogicalPlan, Logi
         public LogicalPlan apply(LogicalPlan plan, AnalyzerContext context) {
             return plan.transformExpressionsUp(
                 org.elasticsearch.xpack.esql.core.expression.function.Function.class,
-                e -> ImplicitCasting.cast(e, context.functionRegistry())
+                e -> ImplicitCasting.cast(e, context.functionRegistry().snapshotRegistry())
             );
         }
 

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java

@@ -188,8 +188,6 @@
 
 public class EsqlFunctionRegistry {
 
-    private static final Map<Class<? extends Function>, List<DataType>> DATA_TYPES_FOR_STRING_LITERAL_CONVERSIONS = new LinkedHashMap<>();
-
     private static final Map<DataType, Integer> DATA_TYPE_CASTING_PRIORITY;
 
     static {
@@ -225,6 +223,7 @@ public class EsqlFunctionRegistry {
     private final Map<String, FunctionDefinition> defs = new LinkedHashMap<>();
     private final Map<String, String> aliases = new HashMap<>();
     private final Map<Class<? extends Function>, String> names = new HashMap<>();
+    private final Map<Class<? extends Function>, List<DataType>> dataTypesForStringLiteralConversions = new LinkedHashMap<>();
 
     private SnapshotFunctionRegistry snapshotRegistry = null;
 
@@ -711,20 +710,8 @@ private static Constructor<?> constructorFor(Class<? extends Function> clazz) {
         return constructors[0];
     }
 
-    private void buildDataTypesForStringLiteralConversion(FunctionDefinition[]... groupFunctions) {
-        for (FunctionDefinition[] group : groupFunctions) {
-            for (FunctionDefinition def : group) {
-                FunctionDescription signature = description(def);
-                DATA_TYPES_FOR_STRING_LITERAL_CONVERSIONS.put(
-                    def.clazz(),
-                    signature.args().stream().map(EsqlFunctionRegistry.ArgSignature::targetDataType).collect(Collectors.toList())
-                );
-            }
-        }
-    }
-
     public List<DataType> getDataTypeForStringLiteralConversion(Class<? extends Function> clazz) {
-        return DATA_TYPES_FOR_STRING_LITERAL_CONVERSIONS.get(clazz);
+        return dataTypesForStringLiteralConversions.get(clazz);
     }
 
     private static class SnapshotFunctionRegistry extends EsqlFunctionRegistry {
@@ -733,6 +720,7 @@ private static class SnapshotFunctionRegistry extends EsqlFunctionRegistry {
                 throw new IllegalStateException("build snapshot function registry for non-snapshot build");
             }
             register(snapshotFunctions());
+            buildDataTypesForStringLiteralConversion(snapshotFunctions());
         }
 
     }
@@ -793,6 +781,18 @@ void register(FunctionDefinition... functions) {
         );
     }
 
+    protected void buildDataTypesForStringLiteralConversion(FunctionDefinition[]... groupFunctions) {
+        for (FunctionDefinition[] group : groupFunctions) {
+            for (FunctionDefinition def : group) {
+                FunctionDescription signature = description(def);
+                dataTypesForStringLiteralConversions.put(
+                    def.clazz(),
+                    signature.args().stream().map(EsqlFunctionRegistry.ArgSignature::targetDataType).collect(Collectors.toList())
+                );
+            }
+        }
+    }
+
     protected FunctionDefinition cloneDefinition(String name, FunctionDefinition definition) {
         return new FunctionDefinition(name, emptyList(), definition.clazz(), definition.builder());
     }

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/util/Delay.java

@@ -21,6 +21,7 @@
 import org.elasticsearch.xpack.esql.core.tree.Source;
 import org.elasticsearch.xpack.esql.core.type.DataType;
 import org.elasticsearch.xpack.esql.evaluator.mapper.EvaluatorMapper;
+import org.elasticsearch.xpack.esql.expression.function.FunctionInfo;
 import org.elasticsearch.xpack.esql.expression.function.Param;
 import org.elasticsearch.xpack.esql.expression.function.scalar.UnaryScalarFunction;
 
@@ -38,6 +39,7 @@
 public class Delay extends UnaryScalarFunction {
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "Delay", Delay::new);
 
+    @FunctionInfo(returnType = { "boolean" }, description = "Sleeps for a duration for every row. For debug purposes only.")
     public Delay(Source source, @Param(name = "ms", type = { "time_duration" }, description = "For how long") Expression ms) {
         super(source, ms);
     }