FnResolver & add support for constrained decimal (#1378)

Author: yliuuuu

CHANGELOG.md

@@ -28,8 +28,10 @@ Thank you to all who have contributed!
 ## [Unreleased]
 
 ### Added
+- Added constrained decimal as valid parameter type to functions that take in numeric parameters. 
 
 ### Changed
+- Function resolution logic: Now the function resolver would match all possible candidate(based on if the argument can be coerced to the Signature parameter type). If there are multiple match it will first attempt to pick the one requires the least cast, then pick the function with the highest precedence. 
 
 ### Deprecated
 

partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/FnResolver.kt

@@ -5,6 +5,7 @@ import org.partiql.planner.internal.ir.Agg
 import org.partiql.planner.internal.ir.Fn
 import org.partiql.planner.internal.ir.Identifier
 import org.partiql.planner.internal.ir.Rex
+import org.partiql.planner.internal.typer.FnResolver.Companion.compareTo
 import org.partiql.types.AnyOfType
 import org.partiql.types.NullType
 import org.partiql.types.StaticType
@@ -247,15 +248,28 @@ internal class FnResolver(private val header: Header) {
 
     /**
      * Functions are sorted by precedence (which is not rigorously defined/specified at the moment).
+     *
+     * This function first attempts to find all possible match for given args
+     * If there are multiple matches, then
+     *   - return the matches that requires the lowest number of coercion
+     *          - This is to match edges like concat(symbol, symbol) which should return symbol
+     *             but because string has higher precedence,
+     *             we also would have concat(cast(symbol as string), cast(symbol as string))
+     *             added to the map first.
+     *   - return the matches which has the highest argument precedence.
      */
     private fun <T : FunctionSignature> match(signatures: List<T>, args: Args): Match<T>? {
+        val candidates = mutableListOf<Match<T>>()
         for (signature in signatures) {
             val mapping = match(signature, args)
             if (mapping != null) {
-                return Match(signature, mapping)
+                candidates.add(Match(signature, mapping))
             }
         }
-        return null
+
+        // Sorted By is stable, we don't have to resort based on parameter type precedence
+        candidates.sortBy { it.mapping.filterNotNull().size }
+        return candidates.firstOrNull()
     }
 
     /**
@@ -288,14 +302,7 @@ internal class FnResolver(private val header: Header) {
                 }
             }
         }
-        // if all elements requires casting, then no match
-        // because there must be another function definition that requires no casting
-        return if (mapping.isEmpty() || mapping.contains(null)) {
-            // we made a match
-            mapping
-        } else {
-            null
-        }
+        return mapping
     }
 
     /**

partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/TypeLattice.kt

@@ -86,6 +86,7 @@ internal class TypeLattice private constructor(
         INT32,
         INT64,
         INT,
+        DECIMAL,
         DECIMAL_ARBITRARY,
         FLOAT32,
         FLOAT64,

partiql-planner/src/main/kotlin/org/partiql/planner/internal/typer/TypeUtils.kt

@@ -121,9 +121,15 @@ private fun StaticType.asRuntimeType(): PartiQLValueType = when (this) {
     is ListType -> PartiQLValueType.LIST
     is SexpType -> PartiQLValueType.SEXP
     is DateType -> PartiQLValueType.DATE
-    is DecimalType -> when (this.precisionScaleConstraint) {
-        is DecimalType.PrecisionScaleConstraint.Constrained -> PartiQLValueType.DECIMAL
-        DecimalType.PrecisionScaleConstraint.Unconstrained -> PartiQLValueType.DECIMAL_ARBITRARY
+    // TODO: Run time decimal type does not model precision scale constraint yet
+    //  despite that we match to Decimal vs Decimal_ARBITRARY (PVT) here
+    //  but when mapping it back to Static Type, (i.e, mapping function return type to Value Type)
+    //  we can only map to Unconstrained decimal (Static Type)
+    is DecimalType -> {
+        when (this.precisionScaleConstraint) {
+            is DecimalType.PrecisionScaleConstraint.Constrained -> PartiQLValueType.DECIMAL
+            DecimalType.PrecisionScaleConstraint.Unconstrained -> PartiQLValueType.DECIMAL_ARBITRARY
+        }
     }
     is FloatType -> PartiQLValueType.FLOAT64
     is GraphType -> error("Graph type missing from runtime types")