Improve nullability detection in new type inference

sqlparser/lib/src/analysis/types/data.dart

@@ -26,11 +26,17 @@ class ResolvedType {
 
   const ResolvedType(
       {this.type, this.hint, this.nullable = false, this.isArray = false});
-  const ResolvedType.bool({bool nullable})
+  const ResolvedType.bool({bool nullable = false})
       : this(type: BasicType.int, hint: const IsBoolean(), nullable: nullable);
 
+  ResolvedType get withoutNullabilityInfo {
+    return nullable == null
+        ? this
+        : ResolvedType(type: type, hint: hint, isArray: isArray);
+  }
+
   ResolvedType withNullable(bool nullable) {
-    return copyWith(nullable: nullable);
+    return nullable == this.nullable ? this : copyWith(nullable: nullable);
   }
 
   ResolvedType toArray(bool array) {

sqlparser/lib/src/analysis/types2/graph/relationships.dart

@@ -56,9 +56,10 @@ class HaveSameType extends TypeRelation {
 class DefaultType extends TypeRelation implements DirectedRelation {
   @override
   final Typeable target;
-  final ResolvedType defaultType;
+  final ResolvedType /*?*/ defaultType;
+  final bool /*?*/ isNullable;
 
-  DefaultType(this.target, this.defaultType);
+  DefaultType(this.target, {this.defaultType, this.isNullable});
 }
 
 enum CastMode { numeric, boolean }

sqlparser/lib/src/analysis/types2/graph/type_graph.dart

@@ -12,13 +12,17 @@ class TypeGraph {
   final Set<MultiSourceRelation> _multiSources = {};
   final List<DefaultType> _defaultTypes = [];
 
-  TypeGraph();
-
   ResolvedType operator [](Typeable t) {
     final normalized = variables.normalize(t);
 
     if (_knownTypes.containsKey(normalized)) {
-      return _knownTypes[normalized];
+      final type = _knownTypes[normalized];
+      final nullability = _knownNullability[normalized];
+
+      if (nullability != null) {
+        return type.withNullable(nullability);
+      }
+      return type;
     }
 
     return null;
@@ -28,7 +32,7 @@ class TypeGraph {
     final normalized = variables.normalize(t);
     _knownTypes[normalized] = type;
 
-    if (type.nullable != null) {
+    if (type.nullable != null && !_knownNullability.containsKey(normalized)) {
       // nullability is known
       _knownNullability[normalized] = type.nullable;
     }
@@ -40,6 +44,10 @@ class TypeGraph {
     _relations.add(relation);
   }
 
+  void markNullability(Typeable t, bool isNullable) {
+    _knownNullability[variables.normalize(t)] = isNullable;
+  }
+
   void performResolve() {
     _indexRelations();
 
@@ -55,8 +63,16 @@ class TypeGraph {
 
     // apply default types
     for (final applyDefault in _defaultTypes) {
-      if (!knowsType(applyDefault.target)) {
-        this[applyDefault.target] = applyDefault.defaultType;
+      final target = applyDefault.target;
+
+      final type = applyDefault.defaultType;
+      if (type != null && !knowsType(target)) {
+        this[target] = applyDefault.defaultType;
+      }
+
+      final nullability = applyDefault.isNullable;
+      if (nullability != null && _knownNullability.containsKey(target)) {
+        markNullability(target, nullability);
       }
     }
   }
@@ -87,13 +103,22 @@ class TypeGraph {
   }
 
   void _propagateManyToOne(MultiSourceRelation edge, List<Typeable> resolved) {
-    if (!knowsType(edge.target)) {
-      final fromTypes = edge.from.map((t) => this[t]).where((e) => e != null);
-      final encapsulated = _encapsulate(fromTypes);
-      if (encapsulated != null) {
-        this[edge.target] = encapsulated;
-        resolved.add(edge.target);
+    if (edge is CopyEncapsulating) {
+      if (!knowsType(edge.target)) {
+        final fromTypes = edge.from.map((t) => this[t]).where((e) => e != null);
+        final encapsulated = _encapsulate(fromTypes);
+        if (encapsulated != null) {
+          this[edge.target] = encapsulated;
+          resolved.add(edge.target);
+        }
       }
+    } else if (edge is NullableIfSomeOtherIs &&
+        !_knownNullability.containsKey(edge.target)) {
+      final nullable = edge.from
+          .map((e) => _knownNullability[e])
+          .any((nullable) => nullable == true);
+
+      _knownNullability[edge.target] = nullable;
     }
   }
 
@@ -108,8 +133,27 @@ class TypeGraph {
   }
 
   ResolvedType /*?*/ _encapsulate(Iterable<ResolvedType> targets) {
-    return targets.fold<ResolvedType>(null, (previous, element) {
-      return previous?.union(element) ?? element;
+    return targets.map((e) => e.withoutNullabilityInfo).fold<ResolvedType>(null,
+        (previous, element) {
+      if (previous == null) return element;
+
+      final previousType = previous.type;
+      final elementType = element.type;
+
+      if (previousType == elementType) return previous;
+      if (previousType == BasicType.nullType) return element;
+
+      bool isIntOrNumeric(BasicType type) {
+        return type == BasicType.int || type == BasicType.real;
+      }
+
+      // encapsulate two different numeric types to real
+      if (isIntOrNumeric(previousType) && isIntOrNumeric(elementType)) {
+        return const ResolvedType(type: BasicType.real);
+      }
+
+      // fallback to text if everything else fails
+      return const ResolvedType(type: BasicType.text);
     });
   }
 
@@ -181,19 +225,6 @@ class _ResolvedVariables {
 }
 
 extension on ResolvedType {
-  ResolvedType union(ResolvedType other) {
-    if (other == this) return this;
-
-    if (other.type == type) {
-      final thisNullable = nullable ?? true;
-      final otherNullable = other.nullable ?? true;
-      return withNullable(thisNullable || otherNullable);
-    }
-
-    // fallback. todo: Support more cases
-    return const ResolvedType(type: BasicType.text, nullable: true);
-  }
-
   ResolvedType cast(CastMode mode) {
     switch (mode) {
       case CastMode.numeric:

sqlparser/lib/src/analysis/types2/resolving_visitor.dart

@@ -189,7 +189,7 @@ class TypeResolver extends RecursiveVisitor<TypeExpectation, void> {
     if (resolved != null) {
       session._checkAndResolve(e, resolved, arg);
     } else if (arg is RoughTypeExpectation) {
-      session._addRelation(DefaultType(e, arg.defaultType()));
+      session._addRelation(DefaultType(e, defaultType: arg.defaultType()));
     }
 
     visitChildren(e, arg);
@@ -434,7 +434,7 @@ class TypeResolver extends RecursiveVisitor<TypeExpectation, void> {
         throw AssertionError(); // required so that this switch compiles
       case 'sum':
         session._addRelation(CopyAndCast(e, params.first, CastMode.numeric));
-        session._addRelation(DefaultType(e, _realType));
+        session._addRelation(DefaultType(e, defaultType: _realType));
         nullableIfChildIs();
         return null;
       case 'lower':
@@ -494,6 +494,9 @@ class TypeResolver extends RecursiveVisitor<TypeExpectation, void> {
       case 'coalesce':
       case 'ifnull':
         session._addRelation(CopyEncapsulating(e, params));
+        for (final param in params) {
+          session._addRelation(DefaultType(param, isNullable: true));
+        }
         return null;
       case 'nullif':
         session._hintNullability(e, true);

sqlparser/lib/src/analysis/types2/types.dart

@@ -46,6 +46,7 @@ class TypeInferenceSession {
   /// This is not currently implemented.
   void _hintNullability(Typeable t, bool nullable) {
     assert(nullable != null);
+    graph.markNullability(t, nullable);
   }
 
   /// Asks the underlying [TypeGraph] to propagate known types via known

sqlparser/test/analysis/types2/misc_cases_test.dart

@@ -30,6 +30,8 @@ const Map<String, ResolvedType> _types = {
   'SELECT (3 * 4) = ?': ResolvedType(type: BasicType.int),
   'SELECT (3 / 4) = ?': ResolvedType(type: BasicType.int),
   'SELECT CURRENT_TIMESTAMP = ?': ResolvedType(type: BasicType.text),
+  "SELECT COALESCE(NULL, 'foo') = ?": ResolvedType(type: BasicType.text),
+  'SELECT NULLIF(3, 4) = ?': ResolvedType(type: BasicType.int, nullable: true),
   'INSERT INTO demo DEFAULT VALUES ON CONFLICT (id) WHERE ? DO NOTHING':
       ResolvedType.bool(),
   'INSERT INTO demo DEFAULT VALUES ON CONFLICT DO UPDATE SET id = id WHERE ?':