SQL AST: ifnull/nullif improvements (#592)

Co-authored-by: Markus Staab <[email protected]>

Author: hemberger

src/SqlAst/IfNullReturnTypeExtension.php

@@ -13,20 +13,79 @@ final class IfNullReturnTypeExtension implements QueryFunctionReturnTypeExtensio
 {
     public function isFunctionSupported(FunctionCall $expression): bool
     {
-        return \in_array($expression->getFunction()->getName(), [BuiltInFunction::IFNULL, BuiltInFunction::NULLIF], true);
+        return \in_array($expression->getFunction()->getName(), [BuiltInFunction::IFNULL], true);
     }
 
-    public function getReturnType(FunctionCall $expression, QueryScope $scope): Type
+    public function getReturnType(FunctionCall $expression, QueryScope $scope): ?Type
     {
         $args = $expression->getArguments();
 
-        $results = [];
-        foreach ($args as $arg) {
-            $argType = $scope->getType($arg);
+        if (2 !== \count($args)) {
+            return null;
+        }
+
+        $argType1 = $scope->getType($args[0]);
+        $argType2 = $scope->getType($args[1]);
+
+        // If arg1 is literal null, arg2 is always returned
+        if ($argType1->isNull()->yes()) {
+            return $argType2;
+        }
 
-            $results[] = $argType;
+        $arg1ContainsNull = TypeCombinator::containsNull($argType1);
+        $arg2ContainsNull = TypeCombinator::containsNull($argType2);
+        $argType1NoNull = TypeCombinator::removeNull($argType1);
+        $argType2NoNull = TypeCombinator::removeNull($argType2);
+
+        // If arg1 can be null, the result can be arg1 or arg2;
+        // otherwise, the result can only be arg1.
+        if ($arg1ContainsNull) {
+            $resultType = TypeCombinator::union($argType1NoNull, $argType2NoNull);
+        } else {
+            $resultType = $argType1;
+        }
+
+        // The result type is always the "more general" of the two args
+        // in the order: string, float, integer.
+        // see https://dev.mysql.com/doc/refman/5.7/en/flow-control-functions.html#function_ifnull
+        if ($this->isResultString($argType1NoNull, $argType2NoNull)) {
+            $resultType = $resultType->toString();
+        } elseif ($this->isResultFloat($argType1NoNull, $argType2NoNull)) {
+            $resultType = $resultType->toFloat();
         }
 
-        return TypeCombinator::union(...$results);
+        // Re-add null if arg2 can contain null
+        if ($arg2ContainsNull) {
+            $resultType = TypeCombinator::addNull($resultType);
+        }
+        return $resultType;
+    }
+
+    private function isResultString(Type $type1, Type $type2): bool
+    {
+        return (
+            // If either arg is a string, the result is a string
+            $type1->isString()->yes() ||
+            $type2->isString()->yes() ||
+
+            // Special case where args are a constant float and an int
+            // results in a numeric string
+            (
+                $type1->isConstantScalarValue()->yes() &&
+                $type1->isFloat()->yes() &&
+                $type2->isInteger()->yes()
+            ) ||
+            (
+                $type2->isConstantScalarValue()->yes() &&
+                $type2->isFloat()->yes() &&
+                $type1->isInteger()->yes()
+            )
+        );
+    }
+
+    private function isResultFloat(Type $type1, Type $type2): bool
+    {
+        // If either arg is a float, the result is a float
+        return $type1->isFloat()->yes() || $type2->isFloat()->yes();
     }
 }

src/SqlAst/NullIfReturnTypeExtension.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace staabm\PHPStanDba\SqlAst;
+
+use PHPStan\Type\NullType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+use SqlFtw\Sql\Expression\BuiltInFunction;
+use SqlFtw\Sql\Expression\FunctionCall;
+
+final class NullIfReturnTypeExtension implements QueryFunctionReturnTypeExtension
+{
+    public function isFunctionSupported(FunctionCall $expression): bool
+    {
+        return \in_array($expression->getFunction()->getName(), [BuiltInFunction::NULLIF], true);
+    }
+
+    public function getReturnType(FunctionCall $expression, QueryScope $scope): ?Type
+    {
+        $args = $expression->getArguments();
+
+        if (2 !== \count($args)) {
+            return null;
+        }
+
+        $argType1 = $scope->getType($args[0]);
+        $argType2 = $scope->getType($args[1]);
+
+        // Return null type if scalar constants are equal
+        if (
+            $argType1->isConstantScalarValue()->yes() &&
+            $argType1->equals($argType2)
+        ) {
+            return new NullType();
+        }
+
+        // If the types *can* be equal, we return the first type or null type
+        if ($argType1->isSuperTypeOf($argType2)->yes() || $argType2->isSuperTypeOf($argType1)->yes()) {
+            return TypeCombinator::addNull($argType1);
+        }
+
+        // Otherwise the first type is returned
+        return $argType1;
+    }
+}

src/SqlAst/QueryScope.php

@@ -59,6 +59,7 @@ public function __construct(Table $fromTable, array $joinedTables)
             new PositiveIntReturnTypeExtension(),
             new CoalesceReturnTypeExtension(),
             new IfNullReturnTypeExtension(),
+            new NullIfReturnTypeExtension(),
             new IfReturnTypeExtension(),
             new ConcatReturnTypeExtension(),
             new InstrReturnTypeExtension(),