milestone_prs: try to fetch src/version first

src/handlers/milestone_prs.rs

@@ -3,6 +3,7 @@ use crate::{
     handlers::Context,
 };
 use anyhow::Context as _;
+use reqwest::StatusCode;
 
 pub async fn handle(ctx: &Context, event: &Event) -> anyhow::Result<()> {
     let e = if let Event::Issue(e) = event {
@@ -39,8 +40,65 @@ pub async fn handle(ctx: &Context, event: &Event) -> anyhow::Result<()> {
         return Ok(());
     };
 
-    // Fetch channel.rs from the upstream repository
+    // Fetch the version from the upstream repository.
+    let version = if let Some(version) = get_version_standalone(ctx, merge_sha).await? {
+        version
+    } else if let Some(version) = get_version_channelrs(ctx, merge_sha).await? {
+        version
+    } else {
+        log::error!("could not find the version of {:?}", merge_sha);
+        return Ok(());
+    };
+
+    if !version.starts_with("1.") && version.len() < 8 {
+        log::error!("Weird version {:?} for {:?}", version, merge_sha);
+        return Ok(());
+    }
+
+    // Associate this merged PR with the version it merged into.
+    //
+    // Note that this should work for rollup-merged PRs too. It will *not*
+    // auto-update when merging a beta-backport, for example, but that seems
+    // fine; we can manually update without too much trouble in that case, and
+    // eventually automate it separately.
+    e.issue.set_milestone(&ctx.github, &version).await?;
+
+    Ok(())
+}
+
+async fn get_version_standalone(ctx: &Context, merge_sha: &str) -> anyhow::Result<Option<String>> {
+    let resp = ctx
+        .github
+        .raw()
+        .get(&format!(
+            "https://raw.githubusercontent.com/rust-lang/rust/{}/src/version",
+            merge_sha
+        ))
+        .send()
+        .await
+        .with_context(|| format!("retrieving src/version for {}", merge_sha))?;
+
+    match resp.status() {
+        StatusCode::OK => {}
+        // Don't treat a 404 as a failure, we'll try another way to retrieve the version.
+        StatusCode::NOT_FOUND => return Ok(None),
+        status => anyhow::bail!(
+            "unexpected status code {} while retrieving src/version for {}",
+            status,
+            merge_sha
+        ),
+    }
+
+    Ok(Some(
+        resp.text()
+            .await
+            .with_context(|| format!("deserializing src/version for {}", merge_sha))?
+            .trim()
+            .to_string(),
+    ))
+}
 
+async fn get_version_channelrs(ctx: &Context, merge_sha: &str) -> anyhow::Result<Option<String>> {
     let resp = ctx
         .github
         .raw()
@@ -66,28 +124,15 @@ pub async fn handle(ctx: &Context, event: &Event) -> anyhow::Result<()> {
             prefix,
             merge_sha
         );
-        return Ok(());
+        return Ok(None);
     };
     let after = &resp[start..];
     let end = if let Some(idx) = after.find('"') {
         idx
     } else {
         log::error!("No suffix in contents of channel.rs at {:?}", merge_sha);
-        return Ok(());
+        return Ok(None);
     };
-    let version = &after[..end];
-    if !version.starts_with("1.") && version.len() < 8 {
-        log::error!("Weird version {:?} for {:?}", version, merge_sha);
-        return Ok(());
-    }
 
-    // Associate this merged PR with the version it merged into.
-    //
-    // Note that this should work for rollup-merged PRs too. It will *not*
-    // auto-update when merging a beta-backport, for example, but that seems
-    // fine; we can manually update without too much trouble in that case, and
-    // eventually automate it separately.
-    e.issue.set_milestone(&ctx.github, version).await?;
-
-    Ok(())
+    Ok(Some(after[..end].to_string()))
 }