[Conductor] Add documentation to individual files (#121277)

* add documentation to files

* Update dev/conductor/core/lib/src/stdio.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/start.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/repository.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/next.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/git.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update dev/conductor/core/lib/src/git.dart
Co-authored-by: Christopher Fujino <fujino@google.com>

* Update stdio.dart

---------
Co-authored-by: Christopher Fujino <fujino@google.com>

dev/conductor/core/lib/src/git.dart

@@ -9,6 +9,12 @@ import 'package:process/process.dart';
 import './globals.dart';
 
 /// A wrapper around git process calls that can be mocked for unit testing.
+///
+/// The `Git` class is a relatively (compared to `Repository`) lightweight
+/// abstraction over invocations to the `git` cli tool. The main
+/// motivation for creating this class was so that it could be overridden in
+/// tests. However, now that tests rely on the [FakeProcessManager] this
+/// abstraction is redundant.
 class Git {
   const Git(this.processManager);
 

dev/conductor/core/lib/src/next.dart

@@ -18,6 +18,11 @@ const String kStateOption = 'state-file';
 const String kYesFlag = 'yes';
 
 /// Command to proceed from one [pb.ReleasePhase] to the next.
+///
+/// After `conductor start`, the rest of the release steps are initiated by the
+/// user via `conductor next`. Thus this command's behavior is conditional upon
+/// which phase of the release the user is currently in. This is implemented
+/// with a switch case statement.
 class NextCommand extends Command<void> {
   NextCommand({
     required this.checkouts,

dev/conductor/core/lib/src/repository.dart

@@ -60,6 +60,39 @@ class Remote {
 }
 
 /// A source code repository.
+///
+/// This class is an abstraction over a git
+/// repository on the local disk. Ideally this abstraction would hide from
+/// the outside libraries what git calls were needed to either read or update
+/// data in the underlying repository. In practice, most of the bugs in the
+/// conductor codebase are related to the git calls made from this and its
+/// subclasses.
+///
+/// Two factors that make this code more complicated than it would otherwise
+/// need to be are:
+/// 1. That any particular invocation of the conductor may or may not already
+/// have the git checkout present on disk, depending on what commands were
+/// previously run; and
+/// 2. The need to provide overrides for integration tests (in particular
+/// the ability to mark a [Repository] instance as a [localUpstream] made
+/// integration tests more hermetic, at the cost of complexity in the
+/// implementation).
+///
+/// The only way to simplify the first factor would be to change the behavior of
+/// the conductor tool to be a long-lived dart process that keeps all of its
+/// state in memory and blocks on user input. This would add the constraint that
+/// the user would need to keep the process running for the duration of a
+/// release, which could potentially take multiple days and users could not
+/// manually change the state of the release process (via editing the JSON
+/// config file). However, these may be reasonable trade-offs to make the
+/// codebase simpler and easier to reason about.
+///
+/// The way to simplify the second factor would be to not put any special
+/// handling in this library for integration tests. This would make integration
+/// tests more difficult/less hermetic, but the production code more reliable.
+/// This is probably the right trade-off to make, as the integration tests were
+/// still not hermetic or reliable, and the main integration test was ultimately
+/// deleted in #84354.
 abstract class Repository {
   Repository({
     required this.name,

dev/conductor/core/lib/src/start.dart

@@ -34,6 +34,16 @@ const String kVersionOverrideOption = 'version-override';
 const String kGithubUsernameOption = 'github-username';
 
 /// Command to print the status of the current Flutter release.
+///
+/// This command has many required options which the user must provide
+/// via command line arguments (or optionally environment variables).
+///
+/// This command is the one with the worst user experience (as the user has to
+/// carefully type out many different options into their terminal) and the one
+/// that would benefit the most from a GUI frontend. This command will
+/// optionally read its options from an environment variable to facilitate a workflow
+/// in which configuration is provided by editing a bash script that sets environment
+/// variables and then invokes the conductor tool.
 class StartCommand extends Command<void> {
   StartCommand({
     required this.checkouts,

dev/conductor/core/lib/src/state.dart

@@ -33,6 +33,19 @@ const String stablePostReleaseMsg = """
   '\t 4. Post announcement flutter release hotline chat room',
   '\t\t Chatroom: ${globals.flutterReleaseHotline}',
 """;
+// The helper functions in `state.dart` wrap the code-generated dart files in
+// `lib/src/proto/`. The most interesting of these functions is:
+
+// * `pb.ConductorState readStateFromFile(File)` - uses the code generated
+// `.mergeFromProto3Json()` method to deserialize the JSON content from the
+// config file into a Dart instance of the `ConductorState` class.
+// * `void writeStateFromFile(File, pb.ConductorState, List<String>)`
+// - similarly calls the `.toProto3Json()` method to serialize a
+// * `ConductorState` instance to a JSON string which is then written to disk.
+// `String phaseInstructions(pb.ConductorState state)` - returns instructions
+// for what the user is supposed to do next based on `state.currentPhase`.
+// * `String presentState(pb.ConductorState state)` - pretty print the state file.
+// This is a little easier to read than the raw JSON.
 
 String luciConsoleLink(String channel, String groupName) {
   assert(

dev/conductor/core/lib/src/stdio.dart

@@ -6,6 +6,14 @@ import 'dart:io' as io;
 
 import 'package:meta/meta.dart';
 
+/// An interface for presenting text output to the user.
+///
+/// Although this could have been simplified by calling `print()`
+/// from the tool, this abstraction allows unit tests to verify output
+/// and allows a GUI frontend to provide an alternative implementation.
+///
+/// User input probably should be part of this class–however it is currently
+/// part of context.dart.
 abstract class Stdio {
   final List<String> logs = <String>[];