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Fix ambiguity about optional variables in non-null args #520

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Merged
merged 2 commits into from
Jul 5, 2019
Merged

Fix ambiguity about optional variables in non-null args #520

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d155188
Fix ambiguity about optional variables in non-null args
leebyron Oct 2, 2018
4d73e50
Review feedback. Now hopefully with even less ambiguity!
Oct 2, 2018
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16 changes: 10 additions & 6 deletions spec/Section 5 -- Validation.md
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Original file line number Diff line number Diff line change
Expand Up @@ -1938,6 +1938,10 @@ A notable exception to typical variable type compatibility is allowing a
variable definition with a nullable type to be provided to a non-null location
as long as either that variable or that location provides a default value.

In the example below, an optional variable `$booleanArg` is allowed to be used
in the non-null argument `optionalBooleanArg` because the field argument is
optional since it provides a default value in the schema.

```graphql example
query booleanArgQueryWithDefault($booleanArg: Boolean) {
arguments {
Expand All @@ -1946,7 +1950,12 @@ query booleanArgQueryWithDefault($booleanArg: Boolean) {
}
```

In the example above, an optional variable is allowed to be used in an non-null argument which provides a default value.
In the example below, an optional variable `$booleanArg` is allowed to be used
in the non-null argument (`nonNullBooleanArg`) because the variable provides
a default value in the query. This behavior is explicitly supported for
compatibility with earlier editions of this specification. GraphQL authoring
tools may wish to report this is a warning with the suggestion to replace
`Boolean` with `Boolean!` to avoid ambiguity.

```graphql example
query booleanArgQueryWithDefault($booleanArg: Boolean = true) {
Expand All @@ -1956,10 +1965,5 @@ query booleanArgQueryWithDefault($booleanArg: Boolean = true) {
}
```

In the example above, a variable provides a default value and can be used in a
non-null argument. This behavior is explicitly supported for compatibility with
earlier editions of this specification. GraphQL authoring tools may wish to
report this is a warning with the suggestion to replace `Boolean` with `Boolean!`.

Note: The value {null} could still be provided to a such a variable at runtime.
A non-null argument must produce a field error if provided a {null} value.