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Clarify 'Values of Correct Type' rule relates to literals #1118

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Clarify 'Values of Correct Type' rule relates to literals #1118

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7fe1b5a
Clarify 'Values of Correct Type' rule does not apply to variables.
benjie Oct 17, 2024
7d86799
Clarify nested variable usages in Values of Correct Type
benjie Oct 17, 2024
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15 changes: 12 additions & 3 deletions spec/Section 5 -- Validation.md
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Expand Up @@ -1303,14 +1303,23 @@ fragment resourceFragment on Resource {

**Formal Specification**

- For each input Value {value} in the document:
- For each literal Input Value {value} in the document:
- Let {type} be the type expected in the position {value} is found.
- {value} must be coercible to {type}.
- {value} must be coercible to {type} (with the assumption that any
{variableUsage} nested within {value} will represent a runtime value of the
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There are two conditions mentioned below, that the variable usage is allowed and that the variable value will coerce at runtime, but only one assumption is mentioned here. Is that intentional?

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{variableUsage} nested within {value} will represent a runtime value of the
{variableUsage} nested within {value} is allowed and will represent a runtime value of the

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It is deliberate: coercion happens at runtime where variables are already resolved; for us to run coercion during validation we need to run a slightly modified coercion - the modification being that it assumes (singular assumption) each variable reference it sees (something coercion would not normally understand) is equivalent to an arbitrary runtime value of that variable's type. It does not need to assume that the variable is allowed, from its point of view the variable exists whether it's allowed or not.

The foundation of that singular assumption is the behaviour of "All Variable Usages Are Allowed" combined with "Coercing Variable Values" - these aren't assumptions, these are specified behaviours.

referenced variable's type).

**Explanatory Text**

Literal values must be compatible with the type expected in the position they
are found as per the coercion rules defined in the Type System chapter.
are found as per the coercion rules defined in the Type System chapter. Variable
values are handled by the rule
[All Variable Usages Are Allowed](#sec-All-Variable-Usages-Are-Allowed).
{ListValue} and {ObjectValue} may nest additional Input Values, some of which
may be a {variableUsage}. Each nested {variableUsage} will be coerced during
execution - see [Coercing Variable Values](#sec-Coercing-Variable-Values) - thus
we assume their runtime value will coerce to the type of the referenced
variable.

The type expected in a position includes the type defined by the argument a
value is provided for, the type defined by an input object field a value is
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