Add support for operationContextParams Endpoints trait (#3755)

## Motivation and Context
<!--- Why is this change required? What problem does it solve? -->
<!--- If it fixes an open issue, please link to the issue here -->
We have to support the new [`operationContextParams`
trait](https://smithy.io/2.0/additional-specs/rules-engine/parameters.html#smithy-rules-operationcontextparams-trait)
for endpoint resolution. This trait specifies JMESPath expressions for
selecting parameter data from the operation's input type.

## Description
<!--- Describe your changes in detail -->
* Add codegen support for the [JMESPath
`keys`](https://jmespath.org/specification.html#keys) function (required
by the trait
[spec](https://smithy.io/2.0/additional-specs/rules-engine/parameters.html#smithy-rules-operationcontextparams-trait))
* Add codegen support for the trait itself. This is achieved by
generating `get_param_name` functions for each param specified in
`operationContextParams`. These functions pull the data out of the input
object and it is added to the endpoint params in the
`${operationName}EndpointParamsInterceptor`

## Testing
<!--- Please describe in detail how you tested your changes -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->
Updated the existing test suite for JMESPath codegen to test the `keys`
function. Updated the existing EndpointsDecoratorTest with an
`operationContextParams` trait specifying one param of each supported
type to test the codegen.

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

Author: landonxjames

CHANGELOG.next.toml

@@ -9,4 +9,16 @@
 # message = "Fix typos in module documentation for generated crates"
 # references = ["smithy-rs#920"]
 # meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "client | server | all"}
-# author = "rcoh"
+# author = "rcoh"
+
+[[smithy-rs]]
+message = "Support `stringArray` type in endpoints params"
+references = ["smithy-rs#3742"]
+meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "client"}
+author = "landonxjames"
+
+[[smithy-rs]]
+message = "Add support for `operationContextParams` Endpoints trait"
+references = ["smithy-rs#3755"]
+meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "client"}
+author = "landonxjames"

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointParamsGenerator.kt

@@ -120,6 +120,8 @@ internal class EndpointParamsGenerator(
         fun memberName(parameterName: String) = Identifier.of(parameterName).rustName()
 
         fun setterName(parameterName: String) = "set_${memberName(parameterName)}"
+
+        fun getterName(parameterName: String) = "get_${memberName(parameterName)}"
     }
 
     fun paramsStruct(): RuntimeType =
@@ -230,7 +232,9 @@ internal class EndpointParamsGenerator(
 
     private fun generateEndpointParamsBuilder(rustWriter: RustWriter) {
         rustWriter.docs("Builder for [`Params`]")
-        Attribute(derive(RuntimeType.Debug, RuntimeType.Default, RuntimeType.PartialEq, RuntimeType.Clone)).render(rustWriter)
+        Attribute(derive(RuntimeType.Debug, RuntimeType.Default, RuntimeType.PartialEq, RuntimeType.Clone)).render(
+            rustWriter,
+        )
         rustWriter.rustBlock("pub struct ParamsBuilder") {
             parameters.toList().forEach { parameter ->
                 val name = parameter.memberName()
@@ -253,7 +257,8 @@ internal class EndpointParamsGenerator(
                         rustBlockTemplate("#{Params}", "Params" to paramsStruct()) {
                             parameters.toList().forEach { parameter ->
                                 rust("${parameter.memberName()}: self.${parameter.memberName()}")
-                                parameter.default.orNull()?.also { default -> rust(".or_else(||Some(${value(default)}))") }
+                                parameter.default.orNull()
+                                    ?.also { default -> rust(".or_else(||Some(${value(default)}))") }
                                 if (parameter.isRequired) {
                                     rustTemplate(
                                         ".ok_or_else(||#{Error}::missing(${parameter.memberName().dq()}))?",

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/endpoint/generators/EndpointParamsInterceptorGenerator.kt

@@ -5,6 +5,7 @@
 
 package software.amazon.smithy.rust.codegen.client.smithy.endpoint.generators
 
+import software.amazon.smithy.jmespath.JmespathExpression
 import software.amazon.smithy.model.node.ArrayNode
 import software.amazon.smithy.model.node.BooleanNode
 import software.amazon.smithy.model.node.Node
@@ -20,16 +21,23 @@ import software.amazon.smithy.rust.codegen.client.smithy.endpoint.rustName
 import software.amazon.smithy.rust.codegen.client.smithy.generators.EndpointTraitBindings
 import software.amazon.smithy.rust.codegen.client.smithy.generators.config.configParamNewtype
 import software.amazon.smithy.rust.codegen.client.smithy.generators.config.loadFromConfigBag
+import software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.RustJmespathShapeTraversalGenerator
+import software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.TraversalBinding
+import software.amazon.smithy.rust.codegen.client.smithy.generators.waiters.TraversedShape
 import software.amazon.smithy.rust.codegen.core.rustlang.CargoDependency
+import software.amazon.smithy.rust.codegen.core.rustlang.RustType
 import software.amazon.smithy.rust.codegen.core.rustlang.RustWriter
 import software.amazon.smithy.rust.codegen.core.rustlang.Writable
+import software.amazon.smithy.rust.codegen.core.rustlang.asRef
 import software.amazon.smithy.rust.codegen.core.rustlang.rust
+import software.amazon.smithy.rust.codegen.core.rustlang.rustBlockTemplate
 import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
 import software.amazon.smithy.rust.codegen.core.rustlang.withBlockTemplate
 import software.amazon.smithy.rust.codegen.core.rustlang.writable
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType
 import software.amazon.smithy.rust.codegen.core.smithy.RuntimeType.Companion.preludeScope
 import software.amazon.smithy.rust.codegen.core.smithy.generators.enforceRequired
+import software.amazon.smithy.rust.codegen.core.smithy.rustType
 import software.amazon.smithy.rust.codegen.core.util.PANIC
 import software.amazon.smithy.rust.codegen.core.util.dq
 import software.amazon.smithy.rust.codegen.core.util.inputShape
@@ -103,10 +111,16 @@ class EndpointParamsInterceptorGenerator(
                     #{Ok}(())
                 }
             }
+
+            // The get_* functions below are generated from JMESPath expressions in the
+            // operationContextParams trait. They target the operation's input shape.
+
+            #{jmespath_getters}
             """,
             *codegenScope,
             "endpoint_prefix" to endpointPrefix(operationShape),
             "param_setters" to paramSetters(operationShape, endpointTypesGenerator.params),
+            "jmespath_getters" to jmesPathGetters(operationShape),
         )
     }
 
@@ -140,6 +154,33 @@ class EndpointParamsInterceptorGenerator(
             rust(".$setterName(#W)", value)
         }
 
+        idx.getOperationContextParams(operationShape).orNull()?.parameters?.forEach { (name, param) ->
+            val setterName = EndpointParamsGenerator.setterName(name)
+            val getterName = EndpointParamsGenerator.getterName(name)
+            val pathValue = param.path
+            val pathExpression = JmespathExpression.parse(pathValue)
+            val pathTraversal =
+                RustJmespathShapeTraversalGenerator(codegenContext).generate(
+                    pathExpression,
+                    listOf(
+                        TraversalBinding.Global(
+                            "input",
+                            TraversedShape.from(model, operationShape.inputShape(model)),
+                        ),
+                    ),
+                )
+
+            when (pathTraversal.outputType) {
+                is RustType.Vec -> {
+                    rust(".$setterName($getterName(_input))")
+                }
+
+                else -> {
+                    rust(".$setterName($getterName(_input).cloned())")
+                }
+            }
+        }
+
         // lastly, allow these to be overridden by members
         memberParams.forEach { (memberShape, param) ->
             val memberName = codegenContext.symbolProvider.toMemberName(memberShape)
@@ -151,6 +192,39 @@ class EndpointParamsInterceptorGenerator(
         }
     }
 
+    private fun jmesPathGetters(operationShape: OperationShape) =
+        writable {
+            val idx = ContextIndex.of(codegenContext.model)
+            val inputShape = operationShape.inputShape(codegenContext.model)
+            val input = symbolProvider.toSymbol(inputShape)
+
+            idx.getOperationContextParams(operationShape).orNull()?.parameters?.forEach { (name, param) ->
+                val getterName = EndpointParamsGenerator.getterName(name)
+                val pathValue = param.path
+                val pathExpression = JmespathExpression.parse(pathValue)
+                val pathTraversal =
+                    RustJmespathShapeTraversalGenerator(codegenContext).generate(
+                        pathExpression,
+                        listOf(
+                            TraversalBinding.Global(
+                                "input",
+                                TraversedShape.from(model, operationShape.inputShape(model)),
+                            ),
+                        ),
+                    )
+
+                rust("// Generated from JMESPath Expression: $pathValue")
+                rustBlockTemplate(
+                    "fn $getterName(input: #{Input}) -> Option<#{Ret}>",
+                    "Input" to input.rustType().asRef(),
+                    "Ret" to pathTraversal.outputType,
+                ) {
+                    pathTraversal.output(this)
+                    rust("Some(${pathTraversal.identifier})")
+                }
+            }
+        }
+
     private fun Node.toWritable(): Writable {
         val node = this
         return writable {

codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/generators/waiters/RustJmespathShapeTraversalGenerator.kt

@@ -128,6 +128,8 @@ data class GeneratedExpression(
 
     internal fun isStringOrEnum(): Boolean = isString() || isEnum()
 
+    internal fun isObject(): Boolean = outputShape is TraversedShape.Object
+
     /** Dereferences this expression if it is a reference. */
     internal fun dereference(namer: SafeNamer): GeneratedExpression =
         if (outputType is RustType.Reference) {
@@ -278,7 +280,7 @@ class JmesPathTraversalCodegenBugException(msg: String?, what: Throwable? = null
  * - Object projections
  * - Multi-select lists (but only when every item in the list is the exact same type)
  * - And/or/not boolean operations
- * - Functions `contains` and `length`. The `keys` function may be supported in the future.
+ * - Functions `contains`, `length`, and `keys`.
  */
 class RustJmespathShapeTraversalGenerator(
     codegenContext: ClientCodegenContext,
@@ -429,6 +431,41 @@ class RustJmespathShapeTraversalGenerator(
                 }
             }
 
+            "keys" -> {
+                if (expr.arguments.size != 1) {
+                    throw InvalidJmesPathTraversalException("Keys function takes exactly one argument")
+                }
+                val arg = generate(expr.arguments[0], bindings)
+                if (!arg.isObject()) {
+                    throw InvalidJmesPathTraversalException("Argument to `keys` function must be an object type")
+                }
+                GeneratedExpression(
+                    identifier = ident,
+                    outputType = RustType.Vec(RustType.String),
+                    outputShape = TraversedShape.Array(null, TraversedShape.String(null)),
+                    output =
+                        writable {
+                            arg.output(this)
+                            val outputShape = arg.outputShape.shape
+                            when (outputShape) {
+                                is StructureShape -> {
+                                    // Can't iterate a struct in Rust so source the keys from smithy
+                                    val keys =
+                                        outputShape.allMembers.keys.joinToString(",") { "${it.dq()}.to_string()" }
+                                    rust("let $ident = vec![$keys];")
+                                }
+
+                                is MapShape -> {
+                                    rust("let $ident = ${arg.identifier}.keys().map(Clone::clone).collect::<Vec<String>>();")
+                                }
+
+                                else ->
+                                    throw UnsupportedJmesPathException("The shape type for an input to the keys function must be a struct or a map, got ${outputShape?.type}")
+                            }
+                        },
+                )
+            }
+
             else -> throw UnsupportedJmesPathException("The `${expr.name}` function is not supported by smithy-rs")
         }
     }