Fix

Author: ondrejmirtes

src/Type/StrictMixedType.php

@@ -163,12 +163,12 @@ public function hasOffsetValueType(Type $offsetType): TrinaryLogic
 
 	public function getOffsetValueType(Type $offsetType): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function setOffsetValueType(?Type $offsetType, Type $valueType, bool $unionValues = true): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function isCallable(): TrinaryLogic
@@ -193,27 +193,27 @@ public function toBoolean(): BooleanType
 
 	public function toNumber(): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function toInteger(): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function toFloat(): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function toString(): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function toArray(): Type
 	{
-		return $this;
+		return new ErrorType();
 	}
 
 	public function inferTemplateTypes(Type $receivedType): TemplateTypeMap

tests/PHPStan/Levels/data/arrayDimFetches-9.json

@@ -0,0 +1,7 @@
+[
+    {
+        "message": "Parameter #1 (mixed) of echo cannot be converted to string.",
+        "line": 15,
+        "ignorable": true
+    }
+]