Parse @bors try commands to replace homu for try builds

src/bors/command/parser.rs

@@ -28,11 +28,22 @@ enum CommandPart<'a> {
 
 pub struct CommandParser {
     prefix: String,
+    parsers: Vec<ParserFn>,
 }
 
 impl CommandParser {
     pub fn new(prefix: String) -> Self {
-        Self { prefix }
+        Self {
+            prefix,
+            parsers: DEFAULT_PARSERS.to_vec(),
+        }
+    }
+
+    pub fn new_try_only(prefix: String) -> Self {
+        Self {
+            prefix,
+            parsers: ONLY_TRY_PARSERS.to_vec(),
+        }
     }
 
     /// Prefix of the bot, used to invoke commands from PR comments.
@@ -52,7 +63,7 @@ impl CommandParser {
             .filter_map(|line| match line.find(&self.prefix) {
                 Some(index) => {
                     let input = &line[index + self.prefix.len()..];
-                    parse_command(input)
+                    parse_command(input, &self.parsers)
                 }
                 None => None,
             })
@@ -116,9 +127,10 @@ fn extract_text_from_markdown(text: &str) -> String {
 }
 
 type ParseResult<T = BorsCommand> = Option<Result<T, CommandParseError>>;
+type ParserFn = fn(&CommandPart<'_>, &[CommandPart<'_>]) -> ParseResult;
 
 // The order of the parsers in the vector is important
-const PARSERS: &[fn(&CommandPart<'_>, &[CommandPart<'_>]) -> ParseResult] = &[
+const DEFAULT_PARSERS: &[ParserFn] = &[
     parser_approval,
     parser_unapprove,
     parser_rollup,
@@ -133,12 +145,14 @@ const PARSERS: &[fn(&CommandPart<'_>, &[CommandPart<'_>]) -> ParseResult] = &[
     parser_tree_ops,
 ];
 
-fn parse_command(input: &str) -> ParseResult {
+const ONLY_TRY_PARSERS: &[ParserFn] = &[parser_try_cancel, parser_try];
+
+fn parse_command(input: &str, parsers: &[ParserFn]) -> ParseResult {
     match parse_parts(input) {
         Ok(parts) => match parts.as_slice() {
             [] => Some(Err(CommandParseError::MissingCommand)),
             [command, arguments @ ..] => {
-                for parser in PARSERS {
+                for parser in parsers {
                     if let Some(result) = parser(command, arguments) {
                         return Some(result);
                     }

src/bors/handlers/mod.rs

@@ -24,7 +24,7 @@ use crate::bors::{BorsContext, Comment, RepositoryState};
 use crate::database::{DelegatedPermission, PullRequestModel};
 use crate::github::{GithubUser, PullRequest, PullRequestNumber};
 use crate::permissions::PermissionType;
-use crate::{PgDbClient, TeamApiClient, load_repositories};
+use crate::{CommandParser, PgDbClient, TeamApiClient, load_repositories};
 use anyhow::Context;
 use octocrab::Octocrab;
 use pr_events::{
@@ -360,7 +360,23 @@ async fn handle_comment(
     use std::fmt::Write;
 
     let pr_number = comment.pr_number;
-    let commands = ctx.parser.parse_commands(&comment.text);
+    let mut commands = ctx.parser.parse_commands(&comment.text);
+
+    // Temporary special case for migration from homu on rust-lang/rust.
+    // Try to parse `@bors try` commands with a hardcoded prefix normally assigned to homu.
+    if repo.repository().owner() == "rust-lang" && repo.repository().name() == "rust" {
+        let homu_commands = CommandParser::new_try_only("@bors".to_string())
+            .parse_commands(&comment.text)
+            .into_iter()
+            .filter(|res| match res {
+                // Let homu handle unknown and missing commands
+                Err(CommandParseError::UnknownCommand(_) | CommandParseError::MissingCommand) => {
+                    false
+                }
+                _ => true,
+            });
+        commands.extend(homu_commands);
+    }
 
     // Bail if no commands
     if commands.is_empty() {