For enum values starting with a digit, prefix the generated symbol with an underscore.

Author: deven

Diff for: codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/rustlang/RustReservedWords.kt

@@ -78,7 +78,8 @@ class RustReservedWordSymbolProvider(
                     return base.toSymbol(shape)
                 }
                 val previousName = base.toMemberName(shape)
-                val escapedName = this.toMemberName(shape)
+                // Prefix leading digit with an underscore to avoid invalid identifiers; allow extra leading underscores.
+                val escapedName = this.toMemberName(shape).replace(Regex("^(_*\\d)"), "_$1")
                 // if the names don't match and it isn't a simple escaping with `r#`, record a rename
                 renamedSymbol.toBuilder().name(escapedName)
                     .letIf(escapedName != previousName && !escapedName.contains("r#")) {

Diff for: codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/EnumGenerator.kt

@@ -102,7 +102,8 @@ class EnumMemberModel(
             parentShape: Shape,
             definition: EnumDefinition,
         ): MaybeRenamed? {
-            val name = definition.name.orNull()?.toPascalCase() ?: return null
+            // Prefix leading digit with an underscore to avoid invalid identifiers; allow extra leading underscores.
+            val name = definition.name.orNull()?.toPascalCase()?.replace(Regex("^(_*\\d)"), "_$1") ?: return null
             // Create a fake member shape for symbol look up until we refactor to use EnumShape
             val fakeMemberShape =
                 MemberShape.builder().id(parentShape.id.withMember(name)).target("smithy.api#String").build()

Diff for: codegen-core/src/test/kotlin/software/amazon/smithy/rust/codegen/core/rustlang/RustReservedWordsTest.kt

@@ -206,5 +206,7 @@ internal class RustReservedWordSymbolProviderTest {
         expectEnumRename("SelfValue", MaybeRenamed("SelfValue_", "SelfValue"))
         expectEnumRename("SelfOther", MaybeRenamed("SelfOther", null))
         expectEnumRename("SELF", MaybeRenamed("SelfValue", "Self"))
+
+        expectEnumRename("_2DBarcode", MaybeRenamed("_2DBarcode", "2DBarcode"))
     }
 }

Diff for: codegen-core/src/test/kotlin/software/amazon/smithy/rust/codegen/core/smithy/generators/EnumGeneratorTest.kt

@@ -50,6 +50,9 @@ class EnumGeneratorTest {
                 { value: "some-value-2",
                   name: "someName2",
                   documentation: "More documentation #escape" },
+                { value: "2D_BARCODE",
+                  name: "_2D_BARCODE",
+                  documentation: "Example with leading digit." },
                 { value: "unknown",
                   name: "unknown",
                   documentation: "It has some docs that #need to be escaped" }
@@ -80,6 +83,14 @@ class EnumGeneratorTest {
             }
         }
 
+        @Test
+        fun `it prefixes enum names with underscore to avoid generating invalid identifiers starting with a digit`() {
+            model("_2D_BARCODE").also { member ->
+                member.derivedName() shouldBe "_2DBarcode"
+                member.name()!!.renamedFrom shouldBe "2DBarcode"
+            }
+        }
+
         @Test
         fun `it should render documentation`() {
             val rendered = RustWriter.forModule("model").also { model("some_name_1").render(it) }.toString()