Escape rust name in enum value variants

CC #257

protobuf-test/src/common/v2/test_ident_pb.proto

@@ -33,3 +33,11 @@ message TestType {
     repeated string struct = 2;
     repeated uint32 ref = 3;
 }
+
+// enum value which is a keyword
+
+enum MyLittleEnum {
+    UNKNOWN = 0;
+    fn = 2;
+    self = 3;
+}

protobuf/src/codegen/enums.rs

@@ -19,18 +19,14 @@ impl EnumValueGen {
         }
     }
 
-    // value name
-    fn name<'a>(&'a self) -> &'a str {
-        self.proto.get_name()
-    }
-
     // enum value
     fn number(&self) -> i32 {
         self.proto.get_number()
     }
 
+    // name of enum variant in generated rust code
     fn rust_name_inner(&self) -> String {
-        self.name().to_string()
+        self.proto.rust_name()
     }
 
     pub fn rust_name_outer(&self) -> String {
@@ -262,7 +258,7 @@ impl<'a> EnumGen<'a> {
                 w.write_line(&format!(
                     "{}::{}",
                     &self.type_name,
-                    &self.enum_with_scope.values()[0].get_name()
+                    &self.enum_with_scope.values()[0].rust_name()
                 ))
             });
         });

protobuf/src/descriptorx.rs

@@ -434,6 +434,21 @@ impl<'a> EnumWithScope<'a> {
     }
 }
 
+pub trait EnumValueDescriptorEx {
+    fn rust_name(&self) -> String;
+}
+
+impl EnumValueDescriptorEx for EnumValueDescriptorProto {
+    fn rust_name(&self) -> String {
+        let mut r = String::new();
+        if rust::is_rust_keyword(self.get_name()) {
+            r.push_str("value_");
+        }
+        r.push_str(self.get_name());
+        r
+    }
+}
+
 impl<'a> WithScope<'a> for EnumWithScope<'a> {
     fn get_scope(&self) -> &Scope<'a> {
         &self.scope