mirror of
https://github.com/letic/terraform-provider-google.git
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292 lines
9.2 KiB
Go
292 lines
9.2 KiB
Go
package function
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import (
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"fmt"
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"github.com/zclconf/go-cty/cty"
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)
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// Function represents a function. This is the main type in this package.
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type Function struct {
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spec *Spec
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}
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// Spec is the specification of a function, used to instantiate
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// a new Function.
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type Spec struct {
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// Params is a description of the positional parameters for the function.
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// The standard checking logic rejects any calls that do not provide
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// arguments conforming to this definition, freeing the function
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// implementer from dealing with such inconsistencies.
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Params []Parameter
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// VarParam is an optional specification of additional "varargs" the
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// function accepts. If this is non-nil then callers may provide an
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// arbitrary number of additional arguments (after those matching with
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// the fixed parameters in Params) that conform to the given specification,
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// which will appear as additional values in the slices of values
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// provided to the type and implementation functions.
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VarParam *Parameter
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// Type is the TypeFunc that decides the return type of the function
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// given its arguments, which may be Unknown. See the documentation
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// of TypeFunc for more information.
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//
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// Use StaticReturnType if the function's return type does not vary
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// depending on its arguments.
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Type TypeFunc
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// Impl is the ImplFunc that implements the function's behavior.
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//
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// Functions are expected to behave as pure functions, and not create
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// any visible side-effects.
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//
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// If a TypeFunc is also provided, the value returned from Impl *must*
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// conform to the type it returns, or a call to the function will panic.
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Impl ImplFunc
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}
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// New creates a new function with the given specification.
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//
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// After passing a Spec to this function, the caller must no longer read from
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// or mutate it.
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func New(spec *Spec) Function {
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f := Function{
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spec: spec,
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}
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return f
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}
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// TypeFunc is a callback type for determining the return type of a function
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// given its arguments.
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//
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// Any of the values passed to this function may be unknown, even if the
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// parameters are not configured to accept unknowns.
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//
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// If any of the given values are *not* unknown, the TypeFunc may use the
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// values for pre-validation and for choosing the return type. For example,
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// a hypothetical JSON-unmarshalling function could return
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// cty.DynamicPseudoType if the given JSON string is unknown, but return
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// a concrete type based on the JSON structure if the JSON string is already
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// known.
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type TypeFunc func(args []cty.Value) (cty.Type, error)
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// ImplFunc is a callback type for the main implementation of a function.
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//
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// "args" are the values for the arguments, and this slice will always be at
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// least as long as the argument definition slice for the function.
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//
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// "retType" is the type returned from the Type callback, included as a
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// convenience to avoid the need to re-compute the return type for generic
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// functions whose return type is a function of the arguments.
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type ImplFunc func(args []cty.Value, retType cty.Type) (cty.Value, error)
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// StaticReturnType returns a TypeFunc that always returns the given type.
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//
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// This is provided as a convenience for defining a function whose return
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// type does not depend on the argument types.
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func StaticReturnType(ty cty.Type) TypeFunc {
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return func([]cty.Value) (cty.Type, error) {
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return ty, nil
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}
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}
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// ReturnType returns the return type of a function given a set of candidate
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// argument types, or returns an error if the given types are unacceptable.
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//
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// If the caller already knows values for at least some of the arguments
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// it can be better to call ReturnTypeForValues, since certain functions may
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// determine their return types from their values and return DynamicVal if
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// the values are unknown.
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func (f Function) ReturnType(argTypes []cty.Type) (cty.Type, error) {
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vals := make([]cty.Value, len(argTypes))
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for i, ty := range argTypes {
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vals[i] = cty.UnknownVal(ty)
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}
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return f.ReturnTypeForValues(vals)
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}
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// ReturnTypeForValues is similar to ReturnType but can be used if the caller
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// already knows the values of some or all of the arguments, in which case
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// the function may be able to determine a more definite result if its
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// return type depends on the argument *values*.
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//
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// For any arguments whose values are not known, pass an Unknown value of
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// the appropriate type.
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func (f Function) ReturnTypeForValues(args []cty.Value) (ty cty.Type, err error) {
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var posArgs []cty.Value
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var varArgs []cty.Value
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if f.spec.VarParam == nil {
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if len(args) != len(f.spec.Params) {
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return cty.Type{}, fmt.Errorf(
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"wrong number of arguments (%d required; %d given)",
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len(f.spec.Params), len(args),
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)
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}
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posArgs = args
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varArgs = nil
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} else {
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if len(args) < len(f.spec.Params) {
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return cty.Type{}, fmt.Errorf(
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"wrong number of arguments (at least %d required; %d given)",
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len(f.spec.Params), len(args),
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)
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}
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posArgs = args[0:len(f.spec.Params)]
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varArgs = args[len(f.spec.Params):]
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}
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for i, spec := range f.spec.Params {
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val := posArgs[i]
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if val.IsNull() && !spec.AllowNull {
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return cty.Type{}, NewArgErrorf(i, "must not be null")
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}
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// AllowUnknown is ignored for type-checking, since we expect to be
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// able to type check with unknown values. We *do* still need to deal
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// with DynamicPseudoType here though, since the Type function might
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// not be ready to deal with that.
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if val.Type() == cty.DynamicPseudoType {
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if !spec.AllowDynamicType {
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return cty.DynamicPseudoType, nil
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}
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} else if errs := val.Type().TestConformance(spec.Type); errs != nil {
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// For now we'll just return the first error in the set, since
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// we don't have a good way to return the whole list here.
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// Would be good to do something better at some point...
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return cty.Type{}, NewArgError(i, errs[0])
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}
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}
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if varArgs != nil {
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spec := f.spec.VarParam
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for i, val := range varArgs {
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realI := i + len(posArgs)
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if val.IsNull() && !spec.AllowNull {
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return cty.Type{}, NewArgErrorf(realI, "must not be null")
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}
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if val.Type() == cty.DynamicPseudoType {
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if !spec.AllowDynamicType {
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return cty.DynamicPseudoType, nil
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}
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} else if errs := val.Type().TestConformance(spec.Type); errs != nil {
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// For now we'll just return the first error in the set, since
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// we don't have a good way to return the whole list here.
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// Would be good to do something better at some point...
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return cty.Type{}, NewArgError(i, errs[0])
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}
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}
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}
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// Intercept any panics from the function and return them as normal errors,
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// so a calling language runtime doesn't need to deal with panics.
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defer func() {
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if r := recover(); r != nil {
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ty = cty.NilType
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err = errorForPanic(r)
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}
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}()
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return f.spec.Type(args)
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}
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// Call actually calls the function with the given arguments, which must
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// conform to the function's parameter specification or an error will be
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// returned.
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func (f Function) Call(args []cty.Value) (val cty.Value, err error) {
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expectedType, err := f.ReturnTypeForValues(args)
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if err != nil {
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return cty.NilVal, err
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}
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// Type checking already dealt with most situations relating to our
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// parameter specification, but we still need to deal with unknown
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// values.
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posArgs := args[:len(f.spec.Params)]
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varArgs := args[len(f.spec.Params):]
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for i, spec := range f.spec.Params {
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val := posArgs[i]
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if !val.IsKnown() && !spec.AllowUnknown {
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return cty.UnknownVal(expectedType), nil
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}
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}
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if f.spec.VarParam != nil {
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spec := f.spec.VarParam
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for _, val := range varArgs {
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if !val.IsKnown() && !spec.AllowUnknown {
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return cty.UnknownVal(expectedType), nil
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}
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}
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}
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var retVal cty.Value
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{
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// Intercept any panics from the function and return them as normal errors,
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// so a calling language runtime doesn't need to deal with panics.
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defer func() {
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if r := recover(); r != nil {
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val = cty.NilVal
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err = errorForPanic(r)
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}
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}()
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retVal, err = f.spec.Impl(args, expectedType)
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if err != nil {
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return cty.NilVal, err
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}
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}
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// Returned value must conform to what the Type function expected, to
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// protect callers from having to deal with inconsistencies.
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if errs := retVal.Type().TestConformance(expectedType); errs != nil {
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panic(fmt.Errorf(
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"returned value %#v does not conform to expected return type %#v: %s",
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retVal, expectedType, errs[0],
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))
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}
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return retVal, nil
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}
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// ProxyFunc the type returned by the method Function.Proxy.
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type ProxyFunc func(args ...cty.Value) (cty.Value, error)
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// Proxy returns a function that can be called with cty.Value arguments
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// to run the function. This is provided as a convenience for when using
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// a function directly within Go code.
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func (f Function) Proxy() ProxyFunc {
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return func(args ...cty.Value) (cty.Value, error) {
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return f.Call(args)
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}
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}
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// Params returns information about the function's fixed positional parameters.
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// This does not include information about any variadic arguments accepted;
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// for that, call VarParam.
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func (f Function) Params() []Parameter {
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new := make([]Parameter, len(f.spec.Params))
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copy(new, f.spec.Params)
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return new
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}
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// VarParam returns information about the variadic arguments the function
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// expects, or nil if the function is not variadic.
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func (f Function) VarParam() *Parameter {
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if f.spec.VarParam == nil {
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return nil
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}
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ret := *f.spec.VarParam
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return &ret
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}
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