From bcca1ba7cfce95929a3757c6cbcdd46a2fa09c3b Mon Sep 17 00:00:00 2001 From: mjmahone Date: Mon, 2 Jan 2023 17:45:26 -0500 Subject: [PATCH] RFC: Fragment Arguments --- spec/Appendix B -- Grammar Summary.md | 6 +- spec/Section 2 -- Language.md | 73 ++++++++- spec/Section 5 -- Validation.md | 227 ++++++++++++++++++++++---- spec/Section 6 -- Execution.md | 53 +++++- 4 files changed, 307 insertions(+), 52 deletions(-) diff --git a/spec/Appendix B -- Grammar Summary.md b/spec/Appendix B -- Grammar Summary.md index 2291ee35f..23ddf92d1 100644 --- a/spec/Appendix B -- Grammar Summary.md +++ b/spec/Appendix B -- Grammar Summary.md @@ -168,12 +168,12 @@ Arguments[Const] : ( Argument[?Const]+ ) Argument[Const] : Name : Value[?Const] -FragmentSpread : ... FragmentName Directives? +FragmentSpread : ... FragmentName Arguments? Directives? InlineFragment : ... TypeCondition? Directives? SelectionSet -FragmentDefinition : fragment FragmentName TypeCondition Directives? -SelectionSet +FragmentDefinition : fragment FragmentName VariablesDefinition? TypeCondition +Directives? SelectionSet FragmentName : Name but not `on` diff --git a/spec/Section 2 -- Language.md b/spec/Section 2 -- Language.md index 1aca650a8..4a9c6b399 100644 --- a/spec/Section 2 -- Language.md +++ b/spec/Section 2 -- Language.md @@ -516,10 +516,10 @@ which returns the result: ## Fragments -FragmentSpread : ... FragmentName Directives? +FragmentSpread : ... FragmentName Arguments? Directives? -FragmentDefinition : fragment FragmentName TypeCondition Directives? -SelectionSet +FragmentDefinition : fragment FragmentName VariablesDefinition? TypeCondition +Directives? SelectionSet FragmentName : Name but not `on` @@ -1209,13 +1209,70 @@ size `60`: **Variable Use Within Fragments** -Variables can be used within fragments. Variables have global scope with a given -operation, so a variable used within a fragment must be declared in any -top-level operation that transitively consumes that fragment. If a variable is -referenced in a fragment and is included by an operation that does not define -that variable, that operation is invalid (see +Variables can be used within fragments. Operation-defined variables have global +scope with a given operation, so a variable used within a fragment must either +be declared in any top-level operation that transitively consumes that fragment, +or by that same fragment as a fragment variable definition. If a variable is +referenced in a fragment is included by an operation where neither the fragment +nor the operation defines that variable, that operation is invalid (see [All Variable Uses Defined](#sec-All-Variable-Uses-Defined)). +## Fragment Variable Definitions + +Fragments may define locally scoped variables. This allows fragments to be +reused while enabling the caller to specify the fragment's behavior. + +For example, the profile picture may need to be a different size depending on +the parent context: + +```graphql example +query withFragmentArguments { + user(id: 4) { + ...dynamicProfilePic(size: 100) + friends(first: 10) { + id + name + ...dynamicProfilePic + } + } +} + +fragment dynamicProfilePic($size: Int! = 50) on User { + profilePic(size: $size) +} +``` + +In this case the `user` will have a larger `profilePic` than those found in the +list of `friends`. + +A fragment-defined variable is scoped to the fragment that defines it. +Fragment-defined variables are allowed to shadow operation-defined variables. + +```graphql example +query withShadowedVariables($size: Int) { + user(id: 4) { + ...variableProfilePic + } + secondUser: user(id: 5) { + ...dynamicProfilePic(size: 10) + } +} + +fragment variableProfilePic on User { + ...dynamicProfilePic(size: $size) +} + +fragment dynamicProfilePic($size: Int!) on User { + profilePic(size: $size) +} +``` + +The profilePic for `user` will be determined by the variables set by the +operation, while `secondUser` will always have a profilePic of size 10. In this +case, the fragment `variableProfilePic` uses the operation-defined variable, +while `dynamicProfilePic` uses the value passed in via the fragment spread's +argument `size`. + ## Type References Type : diff --git a/spec/Section 5 -- Validation.md b/spec/Section 5 -- Validation.md index dceec126b..3f9d7449f 100644 --- a/spec/Section 5 -- Validation.md +++ b/spec/Section 5 -- Validation.md @@ -418,8 +418,15 @@ fragment directFieldSelectionOnUnion on CatOrDog { FieldsInSetCanMerge(set): +- Let {visitedSelections} be the selections in {set} including visiting + fragments and inline fragments and applying any supplied fragment spread + arguments. +- Let {spreadsForName} be the set of fragment spreads with a given name in + {visitedSelections}. +- Given each pair of members {spreadA} and {spreadB} in {spreadsForName}: + - {spreadA} and {spreadB} must have identical sets of arguments. - Let {fieldsForName} be the set of selections with a given response name in - {set} including visiting fragments and inline fragments. + {visitedSelections}. - Given each pair of members {fieldA} and {fieldB} in {fieldsForName}: - {SameResponseShape(fieldA, fieldB)} must be true. - If the parent types of {fieldA} and {fieldB} are equal or if either is not @@ -570,6 +577,50 @@ fragment conflictingDifferingResponses on Pet { } ``` +Fragment spread arguments can also cause fields to fail to merge. + +While the following is valid: + +```graphql example +fragment commandFragment($command: DogCommand!) on Dog { + doesKnowCommand(dogCommand: $command) +} + +fragment potentiallyConflictingArguments( + $commandOne: DogCommand! + $commandTwo: DogCommand! +) on Dog { + ...commandFragment(command: $commandOne) + ...commandFragment(command: $commandTwo) +} + +fragment safeFragmentArguments on Dog { + ...potentiallyConflictingArguments(commandOne: SIT, commandTwo: SIT) +} +``` + +it is only valid because `safeFragmentArguments` uses +`potentiallyConflictingArguments` with the same value for the fragment-defined +variables `commandOne` and `commandTwo`. Therefore `commandFragment` resolves +`doesKnowCommand`'s `dogCommand` argument value to `SIT` in both cases. + +However, by changing the fragment spread argument values: + +```graphql counter-example +fragment conflictingFragmentArguments on Dog { + ...potentiallyConflictingArguments(commandOne: SIT, commandTwo: DOWN) +} +``` + +the response will have two conflicting versions of the `doesKnowCommand` +fragment that cannot merge. + +If two fragment spreads with the same name supply different argument values, +their fields will not be able to merge. In this case, validation fails because +the fragment spread `...commandFragment(command: SIT)` and +`...commandFragment(command: DOWN)` are part of the visited selections that will +be merged. + ### Leaf Field Selections **Formal Specification** @@ -647,8 +698,8 @@ query directQueryOnObjectWithSubFields { ## Arguments -Arguments are provided to both fields and directives. The following validation -rules apply in both cases. +Arguments are provided to fields, fragment spreads and directives. The following +validation rules apply in each case. ### Argument Names @@ -656,14 +707,16 @@ rules apply in both cases. - For each {argument} in the document: - Let {argumentName} be the Name of {argument}. - - Let {argumentDefinition} be the argument definition provided by the parent - field or definition named {argumentName}. + - If the parent is a field or directive: + - Let {argumentDefinition} be the argument or variable definition named + {argumentName} provided by the parent field definition, directive definition + or fragment definition. - {argumentDefinition} must exist. **Explanatory Text** -Every argument provided to a field or directive must be defined in the set of -possible arguments of that field or directive. +Every argument provided to a field or directive or fragment spread must be +defined in the set of possible arguments of that field, directive or fragment. For example the following are valid: @@ -675,9 +728,18 @@ fragment argOnRequiredArg on Dog { fragment argOnOptional on Dog { isHouseTrained(atOtherHomes: true) @include(if: true) } + +fragment withFragmentArg($command: DogCommand) on Dog { + doesKnowCommand(dogCommand: $command) +} + +fragment usesFragmentArg on Dog { + ...withFragmentArg(command: DOWN) +} ``` -the following is invalid since `command` is not defined on `DogCommand`. +The following is invalid since `command` is not defined on +`Dog.doesKnowCommand`. ```graphql counter-example fragment invalidArgName on Dog { @@ -685,6 +747,15 @@ fragment invalidArgName on Dog { } ``` +and this is also invalid as the variable `dogCommand` is not defined on fragment +`withFragmentArg`. + +```graphql counter-example +fragment invalidFragmentArgName on Dog { + ...withFragmentArg(dogCommand: SIT) +} +``` + and this is also invalid as `unless` is not defined on `@include`. ```graphql counter-example @@ -727,9 +798,9 @@ fragment multipleArgsReverseOrder on Arguments { ### Argument Uniqueness -Fields and directives treat arguments as a mapping of argument name to value. -More than one argument with the same name in an argument set is ambiguous and -invalid. +Fields, fragment spreads and directives treat arguments as a mapping of argument +name to value. More than one argument with the same name in an argument set is +ambiguous and invalid. **Formal Specification** @@ -741,10 +812,11 @@ invalid. #### Required Arguments -- For each Field or Directive in the document: - - Let {arguments} be the arguments provided by the Field or Directive. +- For each Field, Fragment Spread or Directive in the document: + - Let {arguments} be the arguments provided by the Field, Directive or + Fragment Spread. - Let {argumentDefinitions} be the set of argument definitions of that Field - or Directive. + or Directive, or the variable definitions of that Fragment. - For each {argumentDefinition} in {argumentDefinitions}: - Let {type} be the expected type of {argumentDefinition}. - Let {defaultValue} be the default value of {argumentDefinition}. @@ -1523,18 +1595,19 @@ query ($foo: Boolean = true, $bar: Boolean = false) { **Formal Specification** -- For every {operation} in the document: - - For every {variable} defined on {operation}: +- For every {operation} and {fragment} in the document: + - Let {operationOrFragment} be that {operation} or {fragment}. + - For every {variable} defined on {operationOrFragment}: - Let {variableName} be the name of {variable}. - Let {variables} be the set of all variables named {variableName} on - {operation}. + {operationOrFragment}. - {variables} must be a set of one. **Explanatory Text** -If any operation defines more than one variable with the same name, it is -ambiguous and invalid. It is invalid even if the type of the duplicate variable -is the same. +If any operation or fragment defines more than one variable with the same name, +it is ambiguous and invalid. It is invalid even if the type of the duplicate +variable is the same. ```graphql counter-example query houseTrainedQuery($atOtherHomes: Boolean, $atOtherHomes: Boolean) { @@ -1563,12 +1636,36 @@ fragment HouseTrainedFragment on Query { } ``` +Likewise, it is valid for both an operation and a fragment to define a variable +with the same name: + +```graphql example +query C($atOtherHomes: Boolean) { + ...HouseTrainedFragment + aDog: dog { + ...HouseTrainedDog + } +} + +fragment HouseTrainedDog($atOtherHomes: Boolean) on Dog { + isHouseTrained(atOtherHomes: $atOtherHomes) +} +``` + +Fragment-defined variables are scoped locally to the fragment that defines them, +and override any operation-defined variable values, so there is never ambiguity +about which value to use. In this case, the value of the argument `atOtherHomes` +within `HouseTrainedFragment` will be the operation-set value, and within +`HouseTrainedDog` will resolve to `null`, as the argument is not set by the +fragment spread in the query `C`. + ### Variables Are Input Types **Formal Specification** -- For every {operation} in a {document}: - - For every {variable} on each {operation}: +- For every {operation} and {fragment} in a {document}: + - Let {operationOrFragment} be that {operation} or {fragment}. + - For every {variable} defined on {operationOrFragment}: - Let {variableType} be the type of {variable}. - {IsInputType(variableType)} must be {true}. @@ -1636,13 +1733,14 @@ query takesCatOrDog($catOrDog: CatOrDog) { transitively. - For each {fragment} in {fragments}: - For each {variableUsage} in scope of {fragment}, variable must be in - {operation}'s variable list. + {fragment}'s or {operation}'s variable list. **Explanatory Text** -Variables are scoped on a per-operation basis. That means that any variable used -within the context of an operation must be defined at the top level of that -operation +Operation-defined Variables are scoped on a per-operation basis, while +Fragment-defined Variables are scoped locally to the fragment. That means that +any variable used within the context of an operation must either be defined at +the top level of that operation or on the fragment that uses that variable. For example: @@ -1669,9 +1767,10 @@ query variableIsNotDefined { ${atOtherHomes} is not defined by the operation. Fragments complicate this rule. Any fragment transitively included by an -operation has access to the variables defined by that operation. Fragments can -appear within multiple operations and therefore variable usages must correspond -to variable definitions in all of those operations. +operation has access to the variables defined by that operation and defined on +the fragment. Fragments can appear within multiple operations and therefore +variable usages not defined on the fragment must correspond to variable +definitions in all of those operations. For example the following is valid: @@ -1768,7 +1867,7 @@ This is because {houseTrainedQueryTwoNotDefined} does not define a variable ${atOtherHomes} but that variable is used by {isHouseTrainedFragment} which is included in that operation. -### All Variables Used +### All Operation Variables Used **Formal Specification** @@ -1776,7 +1875,7 @@ included in that operation. - Let {variables} be the variables defined by that {operation}. - Each {variable} in {variables} must be used at least once in either the operation scope itself or any fragment transitively referenced by that - operation. + operation, excluding fragments that define the same name as an argument. **Explanatory Text** @@ -1828,6 +1927,29 @@ fragment isHouseTrainedWithoutVariableFragment on Dog { } ``` +Fragment arguments can shadow operation variables: fragments that use an +argument are not using the operation-defined variable of the same name. + +Likewise, it would be invalid if the variable was shadowed by a fragment +argument: + +```graphql counter-example +query variableNotUsedWithinFragment($atOtherHomes: Boolean) { + dog { + ...shadowedVariableFragment + } +} + +fragment shadowedVariableFragment($atOtherHomes: Boolean) on Dog { + isHouseTrained(atOtherHomes: $atOtherHomes) +} +``` + +because +{$atOtherHomes} is only referenced in a fragment that defines it as a +locally scoped argument, the operation-defined {$atOtherHomes} +variable is never used. + All operations in a document must use all of their variables. As a result, the following document does not validate. @@ -1853,6 +1975,41 @@ fragment isHouseTrainedFragment on Dog { This document is not valid because {queryWithExtraVar} defines an extraneous variable. +### All Fragment Variables Used + +**Formal Specification** + +- For every {fragment} in the document: + - Let {variables} be the variables defined by that {fragment}. + - Each {variable} in {variables} must be used at least once in the fragment's + scope. + +**Explanatory Text** + +All variables defined by a fragment must be used in that same fragment. Because +fragment-defined variables are scoped to the fragment they are defined on, if +the fragment does not use the variable, then the variable definition is +superfluous. + +For example, the following is invalid: + +```graphql counter-example +query queryWithFragmentArgUnused($atOtherHomes: Boolean) { + dog { + ...fragmentArgUnused(atOtherHomes: $atOtherHomes) + } +} + +fragment fragmentArgUnused($atOtherHomes: Boolean) on Dog { + isHouseTrained +} +``` + +This document is invalid: even though `fragmentArgUnused` is spread with the +argument `atOtherHomes` and `$atOtherHomes` is defined as an operation variable, +there is never a variable `$atOtherHomes` used within the scope of +`fragmentArgUnused`. + ### All Variable Usages Are Allowed **Formal Specification** @@ -1861,8 +2018,12 @@ variable. - Let {variableUsages} be all usages transitively included in the {operation}. - For each {variableUsage} in {variableUsages}: - Let {variableName} be the name of {variableUsage}. - - Let {variableDefinition} be the {VariableDefinition} named {variableName} - defined within {operation}. + - If the usage is within a {fragment} that defines a {variableDefinition} + for {variableName}: + - Let {variableDefinition} be the {VariableDefinition} named + {variableName} defined within {fragment}. + - Otherwise, let {variableDefinition} be the {VariableDefinition} named + {variableName} defined within {operation}. - {IsVariableUsageAllowed(variableDefinition, variableUsage)} must be {true}. diff --git a/spec/Section 6 -- Execution.md b/spec/Section 6 -- Execution.md index 28862ea89..be4758414 100644 --- a/spec/Section 6 -- Execution.md +++ b/spec/Section 6 -- Execution.md @@ -513,17 +513,23 @@ CollectFields(objectType, selectionSet, variableValues, visitedFragments): - Append {selection} to the {groupForResponseKey}. - If {selection} is a {FragmentSpread}: - Let {fragmentSpreadName} be the name of {selection}. - - If {fragmentSpreadName} is in {visitedFragments}, continue with the next - {selection} in {selectionSet}. - - Add {fragmentSpreadName} to {visitedFragments}. - Let {fragment} be the Fragment in the current Document whose name is {fragmentSpreadName}. - If no such {fragment} exists, continue with the next {selection} in {selectionSet}. + - Let {arguments} be the set of arguments on {selection}. + - Let {fragmentSpreadKey} be a unique key of {fragmentSpreadName} and + {arguments}. + - If {fragmentSpreadKey} is in {visitedFragments}, continue with the next + {selection} in {selectionSet}. + - Add {fragmentSpreadKey} to {visitedFragments}. - Let {fragmentType} be the type condition on {fragment}. - If {DoesFragmentTypeApply(objectType, fragmentType)} is false, continue with the next {selection} in {selectionSet}. - - Let {fragmentSelectionSet} be the top-level selection set of {fragment}. + - Let {fragmentWithArgumentSubstitutions} be the result of calling + {SubstituteFragmentArguments(fragment, arguments)}. + - Let {fragmentSelectionSet} be the top-level selection set of + {fragmentWithArgumentSubstitutions}. - Let {fragmentGroupedFieldSet} be the result of calling {CollectFields(objectType, fragmentSelectionSet, variableValues, visitedFragments)}. @@ -562,9 +568,36 @@ DoesFragmentTypeApply(objectType, fragmentType): - if {objectType} is a possible type of {fragmentType}, return {true} otherwise return {false}. +SubstituteFragmentArguments(fragment, arguments): + +- Let {variablesToSubstitute} be initialized to an empty map. +- For each {variableDefinition} in {fragment}: + - Let {variableName} be the name of {variableDefinition}. + - If {variableName} is a key in {arguments}: + - Let {argumentValue} be the value of {variableName} in {arguments}. + - Add {argumentValue} to {variablesToSubstitute} at key {variableName}. + - Otherwise if {variableDefinition} has a default value {defaultValue}: + - Add {defaultValue} to {variablesToSubstitute} at key {variableName}. + - Otherwise: + - Set the key {variableName} in {variableToSubstitute} to a value indicating + the variable is unset. +- Let {substitutedFragment} be a copy of {fragment} where: + - For each {variable} in the selection set of {fragment}: + - Let {variableUsageName} be the name of {variable}. + - If {variableUsageName} is in {variablesToSubstitute}: + - Replace {variable} with the value of {variableUsageName} in + {variablesToSubstitute}. +- Return {substitutedFragment}. + Note: The steps in {CollectFields()} evaluating the `@skip` and `@include` directives may be applied in either order since they apply commutatively. +Note: The unset value used to replace unset fragment-defined arguments in +{SubstituteFragmentArguments()} must not be a variable defined by any operation +that includes the fragment. An example would be to use a variable with a +reserved prefix, like `$__UNSET`, to replace all unset fragment-defined +variables. + ## Executing Fields Each field requested in the grouped field set that is defined on the selected @@ -577,8 +610,8 @@ ExecuteField(objectType, objectValue, fieldType, fields, variableValues): - Let {field} be the first entry in {fields}. - Let {fieldName} be the field name of {field}. -- Let {argumentValues} be the result of {CoerceArgumentValues(objectType, field, - variableValues)} +- Let {argumentValues} be the result of {CoerceFieldArgumentValues(objectType, + field, variableValues)} - Let {resolvedValue} be {ResolveFieldValue(objectType, objectValue, fieldName, argumentValues)}. - Return the result of {CompleteValue(fieldType, fields, resolvedValue, @@ -593,13 +626,17 @@ the type system to have a specific input type. At each argument position in an operation may be a literal {Value}, or a {Variable} to be provided at runtime. -CoerceArgumentValues(objectType, field, variableValues): +CoerceFieldArgumentValues(objectType, field, variableValues): -- Let {coercedValues} be an empty unordered Map. - Let {argumentValues} be the argument values provided in {field}. - Let {fieldName} be the name of {field}. - Let {argumentDefinitions} be the arguments defined by {objectType} for the field named {fieldName}. +- Return {CoerceArgumentValues(argumentDefinitions, argumentValues, + variableValues)} + +CoerceArgumentValues(argumentDefinitions, argumentValues, variableValues): + - For each {argumentDefinition} in {argumentDefinitions}: - Let {argumentName} be the name of {argumentDefinition}. - Let {argumentType} be the expected type of {argumentDefinition}.