feat: implement the multipleOf keyword

Author: mstream

docs/src/examples/json-schema-change-compatibility-checks.md

@@ -1,4 +1,3 @@
----
 ## JSON Schema Change Compatibility Checks
 **Backward compatibility** - an ability of a system to understand input intended for previous versions of itself
 
@@ -39,6 +38,10 @@ Examples:
 - [Expected JSON value types including integer is extended by number](#expected-json-value-types-including-integer-is-extended-by-number)
 - [Expected JSON value types including integer and number is reduced by integer](#expected-json-value-types-including-integer-and-number-is-reduced-by-integer)
 - [Expected JSON value types including integer and number is reuced by number](#expected-json-value-types-including-integer-and-number-is-reuced-by-number)
+- [the new value of multipleOf is divisible by the old one](#the-new-value-of-multipleof-is-divisible-by-the-old-one)
+- [the old value of multipleOf is divisible by the new one](#the-old-value-of-multipleof-is-divisible-by-the-new-one)
+- [old and new value of multipleOf are not each other's factors](#old-and-new-value-of-multipleof-are-not-each-other's-factors)
+---
 ### No JSON schema differences
 When there is not JSON schema differences, schema change is fully compatible.
 
@@ -51,6 +54,7 @@ no differences
 ```
 full
 ```
+---
 ### Expected JSON value type changes from null to boolean
 Because no boolean value can satisfy null JSON type constraint, and vice versa, such a change is incompatible.
 
@@ -68,6 +72,7 @@ Because no boolean value can satisfy null JSON type constraint, and vice versa,
 ```
 none
 ```
+---
 ### Expected JSON value type changes from integer to number
 Because every integer is a number, but not vice versa, such a change is backward compatible.
 
@@ -85,6 +90,7 @@ Because every integer is a number, but not vice versa, such a change is backward
 ```
 backward
 ```
+---
 ### Expected JSON value type changes from number to integer
 Because every integer is a number, but not vice versa, such a change is forward compatible.
 
@@ -102,6 +108,7 @@ Because every integer is a number, but not vice versa, such a change is forward
 ```
 forward
 ```
+---
 ### Expected JSON value types is extended
 Because more value types than before are accepted, this change is backward compatible.
 
@@ -120,6 +127,7 @@ Because more value types than before are accepted, this change is backward compa
 ```
 backward
 ```
+---
 ### Expected JSON value types is reduced
 Because less value types than before are accepted, this change is forward compatible.
 
@@ -138,6 +146,7 @@ Because less value types than before are accepted, this change is forward compat
 ```
 forward
 ```
+---
 ### Expected JSON value types including number is extended by integer
 Because every integer is a number, such a change is fully compatible.
 
@@ -156,6 +165,7 @@ Because every integer is a number, such a change is fully compatible.
 ```
 full
 ```
+---
 ### Expected JSON value types including integer is extended by number
 Because not every integer is a number, such a change is backward compatible.
 
@@ -174,6 +184,7 @@ Because not every integer is a number, such a change is backward compatible.
 ```
 backward
 ```
+---
 ### Expected JSON value types including integer and number is reduced by integer
 Because every integer is a number, such a change is fully compatible.
 
@@ -192,6 +203,7 @@ Because every integer is a number, such a change is fully compatible.
 ```
 full
 ```
+---
 ### Expected JSON value types including integer and number is reuced by number
 Because not every integer is a number, such a change is forward compatible.
 
@@ -210,3 +222,48 @@ Because not every integer is a number, such a change is forward compatible.
 ```
 forward
 ```
+---
+### the new value of multipleOf is divisible by the old one
+Because every multiple the new value is also a multiple of the old value, such a change is backward compatible
+
+#### Input
+##### JSON schema differences
+```
+-
+  Schema path: #
+  multipleOf changed from 2.0 to 4.0
+```
+#### Output
+```
+backward
+```
+---
+### the old value of multipleOf is divisible by the new one
+Because every multiple the old value is also a multiple of the new value, such a change is forward compatible
+
+#### Input
+##### JSON schema differences
+```
+-
+  Schema path: #
+  multipleOf changed from 4.0 to 2.0
+```
+#### Output
+```
+forward
+```
+---
+### old and new value of multipleOf are not each other's factors
+In this situation, there are potentially some numbers that are not divisible by neither of multipleOf values. Therefore, such a change is incompatible.
+
+#### Input
+##### JSON schema differences
+```
+-
+  Schema path: #
+  multipleOf changed from 2.0 to 5.0
+```
+#### Output
+```
+none
+```

docs/src/examples/json-schema-difference-calculation.md

@@ -1,4 +1,3 @@
----
 ## JSON Schema Difference Calculation
 TODO
 
@@ -8,6 +7,8 @@ Examples:
 
 - [Comparing identical schemata](#comparing-identical-schemata)
 - [Changing expected JSON value type from null to boolean](#changing-expected-json-value-type-from-null-to-boolean)
+- [Changing multipleOf value](#changing-multipleof-value)
+---
 ### Comparing identical schemata
 When two identical schemata are compared, no difference should be found.
 
@@ -24,6 +25,7 @@ false
 ```
 no differences
 ```
+---
 ### Changing expected JSON value type from null to boolean
 Any change in expected JSON value type should be accounted as a difference.
 
@@ -45,3 +47,22 @@ Any change in expected JSON value type should be accounted as a difference.
   to
   - boolean
 ```
+---
+### Changing multipleOf value
+TODO
+
+#### Input
+##### Previous JSON schema
+```json
+{"multipleOf":2,"type":["number"]}
+```
+##### Next JSON schema
+```json
+{"multipleOf":4,"type":["number"]}
+```
+#### Output
+```
+-
+  Schema path: #
+  multipleOf changed from 2.0 to 4.0
+```

docs/src/examples/json-values-validation.md

@@ -1,4 +1,3 @@
----
 ## JSON Values Validation
 TODO
 
@@ -8,9 +7,14 @@ Examples:
 
 - [A null value against a schema accepting only null values](#a-null-value-against-a-schema-accepting-only-null-values)
 - [A boolean value against a schema accepting only null values](#a-boolean-value-against-a-schema-accepting-only-null-values)
+- [An whole number value against a schema accepting only numbers](#an-whole-number-value-against-a-schema-accepting-only-numbers)
+- [A fractional number value against a schema accepting only integers](#a-fractional-number-value-against-a-schema-accepting-only-integers)
 - [A boolean value against a schema accepting only null and string values](#a-boolean-value-against-a-schema-accepting-only-null-and-string-values)
 - [An array with 2 out of 5 items not matching the desired item type](#an-array-with-2-out-of-5-items-not-matching-the-desired-item-type)
 - [An array with forbidden duplicate value.](#an-array-with-forbidden-duplicate-value.)
+- [Number 7.5 against a schema accepting only multiples of 2.5](#number-7.5-against-a-schema-accepting-only-multiples-of-2.5)
+- [Number 7 against a schema accepting only multiples of 2.5](#number-7-against-a-schema-accepting-only-multiples-of-2.5)
+---
 ### A null value against a schema accepting only null values
 A null value conforms to the schema.
 
@@ -27,6 +31,7 @@ null
 ```
 ✓ no violations
 ```
+---
 ### A boolean value against a schema accepting only null values
 A boolean value does not conform to the schema as only null values do.
 
@@ -46,6 +51,44 @@ true
   JSON path: $
   Invalid type. Expected null but got boolean.
 ```
+---
+### An whole number value against a schema accepting only numbers
+All whole number values conform to the schema as every integer is a number.
+
+#### Input
+##### JSON schema
+```json
+{"type":["number"]}
+```
+##### JSON
+```json
+1
+```
+#### Output
+```
+✓ no violations
+```
+---
+### A fractional number value against a schema accepting only integers
+Not all number values conform to the schema as not every number is a integer.
+
+#### Input
+##### JSON schema
+```json
+{"type":["integer"]}
+```
+##### JSON
+```json
+1.5
+```
+#### Output
+```
+✗
+  Schema path: #/type
+  JSON path: $
+  Invalid type. Expected integer but got number.
+```
+---
 ### A boolean value against a schema accepting only null and string values
 A boolean value does not conform to the schema as only null or string values do.
 
@@ -65,6 +108,7 @@ true
   JSON path: $
   Invalid type. Expected null or string but got boolean.
 ```
+---
 ### An array with 2 out of 5 items not matching the desired item type
 When schema requires items to conform to a certain schema, every single value in the array has to.
 
@@ -92,6 +136,7 @@ When schema requires items to conform to a certain schema, every single value in
     JSON path: $[3]
     Invalid type. Expected null but got boolean.
 ```
+---
 ### An array with forbidden duplicate value.
 When schema requires items to be unique, any duplicate occurrence of any value will cause a validation failure.
 
@@ -127,3 +172,40 @@ When schema requires items to be unique, any duplicate occurrence of any value w
     JSON path: $[5]
     Non-unique array item.
 ```
+---
+### Number 7.5 against a schema accepting only multiples of 2.5
+Number 7.5 conforms to the schema as 7.5 is 2.5 times 3.
+
+#### Input
+##### JSON schema
+```json
+{"multipleOf":2.5,"type":["number"]}
+```
+##### JSON
+```json
+7.5
+```
+#### Output
+```
+✓ no violations
+```
+---
+### Number 7 against a schema accepting only multiples of 2.5
+Number 7 does not conform the schema as 7.5 is not a multiple of 2.5.
+
+#### Input
+##### JSON schema
+```json
+{"multipleOf":2.5,"type":["number"]}
+```
+##### JSON
+```json
+7
+```
+#### Output
+```
+✗
+  Schema path: #/multipleOf
+  JSON path: $
+  7.0 is not a multiple of 2.5
+```

src/purs/JsonSchema.purs

@@ -27,6 +27,7 @@ instance Show JsonSchema where
 
 type Keywords =
   { items ∷ Maybe JsonSchema
+  , multipleOf ∷ Maybe Number
   , not ∷ Maybe JsonSchema
   , required ∷ Set String
   , typeKeyword ∷ Maybe (Set JsonValueType)
@@ -36,6 +37,7 @@ type Keywords =
 defaultKeywords ∷ Keywords
 defaultKeywords =
   { items: Nothing
+  , multipleOf: Nothing
   , not: Nothing
   , required: Set.empty
   , typeKeyword: Nothing

src/purs/JsonSchema/Codec/Parsing.purs

@@ -11,8 +11,10 @@ import Data.Maybe (Maybe(..), maybe)
 import Data.Set (Set)
 import Data.Set as Set
 import Data.Traversable (traverse)
+import Foreign.Object (Object)
 import Foreign.Object as Object
 import JsonSchema (JsonSchema(..), JsonValueType(..))
+import JsonSchema as Schema
 
 parseSchema ∷ Json → String \/ JsonSchema
 parseSchema json = parseBooleanSchema json <|> parseObjectSchema json
@@ -30,33 +32,51 @@ parseObjectSchema keywordsJson = do
     (parsingErrorMessage "schema is not a JSON object")
     (A.toObject keywordsJson)
 
-  items ← maybe (Right Nothing)
+  items ← maybe (Right Schema.defaultKeywords.items)
     (map Just <<< parseSchema)
     (Object.lookup "items" schemaObject)
 
-  not ← maybe (Right Nothing)
+  multipleOf ← parseMultipleOf schemaObject
+
+  not ← maybe (Right Schema.defaultKeywords.not)
     (map Just <<< parseSchema)
     (Object.lookup "not" schemaObject)
 
-  required ← maybe (Right Set.empty)
+  required ← maybe (Right Schema.defaultKeywords.required)
     parseRequiredKeywordSpec
     (Object.lookup "required" schemaObject)
 
   typeKeyword ← case Object.lookup "type" schemaObject of
     Just typeKeywordSpecJson →
       Just <$> parseTypeKeywordSpec typeKeywordSpecJson
     Nothing →
-      Right Nothing
+      Right Schema.defaultKeywords.typeKeyword
 
-  uniqueItems ← maybe (Right false)
+  uniqueItems ← maybe (Right Schema.defaultKeywords.uniqueItems)
     ( \json →
-        if A.isNull json then Right false
+        if A.isNull json then Right Schema.defaultKeywords.uniqueItems
         else note "Unique items is not a boolean." $ A.toBoolean json
     )
     (Object.lookup "uniqueItems" schemaObject)
 
   pure $ ObjectSchema
-    { items, not, required, typeKeyword, uniqueItems }
+    { items, multipleOf, not, required, typeKeyword, uniqueItems }
+
+parseMultipleOf ∷ Object Json → String \/ Maybe Number
+parseMultipleOf = Object.lookup "multipleOf" >>> case _ of
+  Just json →
+    if A.isNull json then Right default
+    else case A.toNumber json of
+      Just x →
+        if x > zero then Right $ Just x
+        else Left "multipleOf must be greater than zero."
+      Nothing →
+        Left "multipleOf is not a number."
+  Nothing →
+    Right default
+  where
+  default ∷ Maybe Number
+  default = Schema.defaultKeywords.multipleOf
 
 parseTypeKeywordSpec ∷ Json → String \/ Set JsonValueType
 parseTypeKeywordSpec specJson = do