fix: fq_message_name should begin with one dot

When package name is empty, but type_path is filled, the fq_message_name should begin with a single dot.

Two duplicate implementations are moved to a separate function.

prost-build/src/code_generator.rs

@@ -122,18 +122,7 @@ impl<'a> CodeGenerator<'a> {
         debug!("  message: {:?}", message.name());
 
         let message_name = message.name().to_string();
-        let fq_message_name = format!(
-            "{}{}{}{}.{}",
-            if self.package.is_empty() && self.type_path.is_empty() {
-                ""
-            } else {
-                "."
-            },
-            self.package.trim_matches('.'),
-            if self.type_path.is_empty() { "" } else { "." },
-            self.type_path.join("."),
-            message_name,
-        );
+        let fq_message_name = self.fq_name(&message_name);
 
         // Skip external types.
         if self.extern_paths.resolve_ident(&fq_message_name).is_some() {
@@ -699,18 +688,7 @@ impl<'a> CodeGenerator<'a> {
         let enum_name = to_upper_camel(proto_enum_name);
 
         let enum_values = &desc.value;
-        let fq_proto_enum_name = format!(
-            "{}{}{}{}.{}",
-            if self.package.is_empty() && self.type_path.is_empty() {
-                ""
-            } else {
-                "."
-            },
-            self.package.trim_matches('.'),
-            if self.type_path.is_empty() { "" } else { "." },
-            self.type_path.join("."),
-            proto_enum_name,
-        );
+        let fq_proto_enum_name = self.fq_name(proto_enum_name);
 
         if self
             .extern_paths
@@ -1063,6 +1041,18 @@ impl<'a> CodeGenerator<'a> {
             .as_ref()
             .map_or(false, FieldOptions::deprecated)
     }
+
+    /// Returns the fully-qualified name, starting with a dot
+    fn fq_name(&self, message_name: &str) -> String {
+        format!(
+            "{}{}{}{}.{}",
+            if self.package.is_empty() { "" } else { "." },
+            self.package.trim_matches('.'),
+            if self.type_path.is_empty() { "" } else { "." },
+            self.type_path.join("."),
+            message_name,
+        )
+    }
 }
 
 /// Returns `true` if the repeated field type can be packed.