Allow file descriptor be generated without --include_source_info (#786)

* Allow file descriptor be generated without --include_source_info

The file descriptor sets generated by rules_proto in bazel don't have
this by default, so this allows some flexibility for users to reuse
results that are already available to them.  It's fairly trivial
adjustment so it seemed reasonable to me to allow the flexibility.

* revert breaking changes and add default

prost-build/src/ast.rs

@@ -5,7 +5,7 @@ use pulldown_cmark::{CodeBlockKind, Event, Options, Parser, Tag};
 use regex::Regex;
 
 /// Comments on a Protobuf item.
-#[derive(Debug, Clone)]
+#[derive(Debug, Default, Clone)]
 pub struct Comments {
     /// Leading detached blocks of comments.
     pub leading_detached: Vec<Vec<String>>,

prost-build/src/code_generator.rs

@@ -29,7 +29,7 @@ enum Syntax {
 pub struct CodeGenerator<'a> {
     config: &'a mut Config,
     package: String,
-    source_info: SourceCodeInfo,
+    source_info: Option<SourceCodeInfo>,
     syntax: Syntax,
     message_graph: &'a MessageGraph,
     extern_paths: &'a ExternPaths,
@@ -51,16 +51,14 @@ impl<'a> CodeGenerator<'a> {
         file: FileDescriptorProto,
         buf: &mut String,
     ) {
-        let mut source_info = file
-            .source_code_info
-            .expect("no source code info in request");
-        source_info.location.retain(|location| {
-            let len = location.path.len();
-            len > 0 && len % 2 == 0
+        let source_info = file.source_code_info.map(|mut s| {
+            s.location.retain(|loc| {
+                let len = loc.path.len();
+                len > 0 && len % 2 == 0
+            });
+            s.location.sort_by(|a, b| a.path.cmp(&b.path));
+            s
         });
-        source_info
-            .location
-            .sort_by_key(|location| location.path.clone());
 
         let syntax = match file.syntax.as_ref().map(String::as_str) {
             None | Some("proto2") => Syntax::Proto2,
@@ -569,14 +567,13 @@ impl<'a> CodeGenerator<'a> {
         self.buf.push_str("}\n");
     }
 
-    fn location(&self) -> &Location {
-        let idx = self
-            .source_info
+    fn location(&self) -> Option<&Location> {
+        let source_info = self.source_info.as_ref()?;
+        let idx = source_info
             .location
             .binary_search_by_key(&&self.path[..], |location| &location.path[..])
             .unwrap();
-
-        &self.source_info.location[idx]
+        Some(&source_info.location[idx])
     }
 
     fn append_doc(&mut self, fq_name: &str, field_name: Option<&str>) {
@@ -589,7 +586,9 @@ impl<'a> CodeGenerator<'a> {
             self.config.disable_comments.get(fq_name).next().is_none()
         };
         if append_doc {
-            Comments::from_location(self.location()).append_with_indent(self.depth, self.buf)
+            if let Some(comments) = self.location().map(Comments::from_location) {
+                comments.append_with_indent(self.depth, self.buf);
+            }
         }
     }
 
@@ -715,7 +714,7 @@ impl<'a> CodeGenerator<'a> {
 
         for variant in variant_mappings.iter() {
             self.push_indent();
-            self.buf.push_str("\"");
+            self.buf.push('\"');
             self.buf.push_str(variant.proto_name);
             self.buf.push_str("\" => Some(Self::");
             self.buf.push_str(&variant.generated_variant_name);
@@ -742,7 +741,10 @@ impl<'a> CodeGenerator<'a> {
         let name = service.name().to_owned();
         debug!("  service: {:?}", name);
 
-        let comments = Comments::from_location(self.location());
+        let comments = self
+            .location()
+            .map(Comments::from_location)
+            .unwrap_or_default();
 
         self.path.push(2);
         let methods = service
@@ -751,8 +753,12 @@ impl<'a> CodeGenerator<'a> {
             .enumerate()
             .map(|(idx, mut method)| {
                 debug!("  method: {:?}", method.name());
+
                 self.path.push(idx as i32);
-                let comments = Comments::from_location(self.location());
+                let comments = self
+                    .location()
+                    .map(Comments::from_location)
+                    .unwrap_or_default();
                 self.path.pop();
 
                 let name = method.name.take().unwrap();

prost-build/src/lib.rs

@@ -664,8 +664,7 @@ impl Config {
 
     /// In combination with with `file_descriptor_set_path`, this can be used to provide a file
     /// descriptor set as an input file, rather than having prost-build generate the file by calling
-    /// protoc.  Prost-build does require that the descriptor set was generated with
-    /// --include_source_info.
+    /// protoc.
     ///
     /// In `build.rs`:
     ///