Fix name collision in generated union functions

CHANGELOG.md

@@ -1,11 +1,13 @@
 vNext (Month Day, Year)
 -----------------------
+
 **New this week**
 
 - (When complete) Add profile file provider for region (#594, #xyz)
 - Add experimental `dvr` module to smithy-client. This will enable easier testing of HTTP traffic. (#640)
 - Add profile file credential provider implementation. This implementation currently does not support credential sources
   for assume role providers other than environment variables. (#640)
+- :bug: Fix name collision that occurred when a model had both a union and a structure named `Result` (#643)
 
 v0.20 (August 10th, 2021)
 --------------------------

codegen-test/build.gradle.kts

@@ -61,7 +61,13 @@ val CodegenTests = listOf(
     ),
     CodegenTest(
         "crate#Config",
-        "naming_test", """
+        "naming_test_ops", """
+            , "codegen": { "renameErrors": false }
+        """.trimIndent()
+    ),
+    CodegenTest(
+        "naming_obs_structs#NamingObstacleCourseStructs",
+        "naming_test_structs", """
             , "codegen": { "renameErrors": false }
         """.trimIndent()
     )

codegen-test/model/naming-obstacle-course-structs.smithy

@@ -0,0 +1,53 @@
+$version: "1.0"
+namespace naming_obs_structs
+
+use aws.protocols#awsJson1_1
+use aws.api#service
+
+/// Confounds model generation machinery with lots of problematic names
+@awsJson1_1
+@service(sdkId: "NamingObstacleCourseStructs")
+service NamingObstacleCourseStructs {
+    version: "2006-03-01",
+    operations: [
+       Structs,
+    ]
+}
+
+structure SomethingElse {
+    result: Result,
+    resultList: ResultList,
+    option: Option,
+    optionList: OptionList,
+    someUnion: SomeUnion,
+}
+
+union SomeUnion {
+    Result: Result,
+    Option: Option,
+}
+
+structure Result {
+    value: String,
+}
+list ResultList {
+    member: Result,
+}
+structure Option {
+    value: String,
+}
+list OptionList {
+    member: Result,
+}
+
+structure StructsInputOutput {
+    result: Result,
+    resultList: ResultList,
+    option: Option,
+    optionList: OptionList,
+    somethingElse: SomethingElse,
+}
+operation Structs {
+    input: StructsInputOutput,
+    output: StructsInputOutput
+}

codegen/src/main/kotlin/software/amazon/smithy/rust/codegen/smithy/generators/UnionGenerator.kt

@@ -51,7 +51,7 @@ class UnionGenerator(
                 if (sortedMembers.size == 1) {
                     Attribute.Custom("allow(irrefutable_let_patterns)").render(this)
                 }
-                rustBlock("pub fn as_$funcNamePart(&self) -> Result<&#T, &Self>", memberSymbol) {
+                rustBlock("pub fn as_$funcNamePart(&self) -> std::result::Result<&#T, &Self>", memberSymbol) {
                     rust("if let ${unionSymbol.name}::$variantName(val) = &self { Ok(&val) } else { Err(&self) }")
                 }
                 rustBlock("pub fn is_$funcNamePart(&self) -> bool") {