internal/task: add detection for repeated task runs

The expected happy path is that the "between freeze start and RC 1"
workflow is run once to completion and not again. Still, it might
happen that we run it more than once, intentionally or accidentally.
Add logic, within reason, to detect repeated runs and avoid taking
inappropriate actions.

For golang/go#70655.

Change-Id: Ifb4bcc4e5aea0087784337fc3e84a90e54a1af18
Reviewed-on: https://go-review.googlesource.com/c/build/+/633755
Reviewed-by: Michael Knyszek <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: dmitshur

internal/task/releasecycle.go

@@ -6,6 +6,7 @@ package task
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io/fs"
 	"path"
@@ -55,6 +56,18 @@ func (t ReleaseCycleTasks) PromoteNextAPI(ctx *wf.TaskContext, version int, revi
 	}
 	ctx.Printf("Using commit %q as the branch head.", commit)
 
+	// Confirm that "api/go1.{version}.txt" hasn't already been made.
+	promotedAPIFile := path.Join("api", fmt.Sprintf("go1.%d.txt", version))
+	_, err = t.Gerrit.ReadFile(ctx, "go", commit, promotedAPIFile)
+	if err == nil {
+		ctx.Printf("The %s file is already created, so refusing to run this task (and tasks that depend on it).", promotedAPIFile)
+		return PromotedAPI{}, fmt.Errorf("%s already exists; the scope of this task is to create that file only", promotedAPIFile)
+	} else if errors.Is(err, gerrit.ErrResourceNotExist) {
+		// OK. We'll be creating it below.
+	} else if err != nil {
+		return PromotedAPI{}, err
+	}
+
 	// Read api/next files at commit.
 	var files = make(map[string]string)
 	des, err := t.Gerrit.ReadDir(ctx, "go", commit, "api/next")
@@ -89,7 +102,7 @@ func (t ReleaseCycleTasks) PromoteNextAPI(ctx *wf.TaskContext, version int, revi
 	for _, api := range promoted.APIs {
 		fmt.Fprintln(&buf, api)
 	}
-	files[path.Join("api", fmt.Sprintf("go1.%d.txt", version))] = buf.String()
+	files[promotedAPIFile] = buf.String()
 
 	// Beyond this point we want retries to be done manually, not automatically.
 	ctx.DisableRetries()
@@ -238,6 +251,24 @@ func (t ReleaseCycleTasks) MergeNextRelnoteAndAddToWebsite(ctx *wf.TaskContext,
 	}
 	ctx.Printf("Using commit %q as the branch head.", commit)
 
+	// Confirm that fragments haven't been merged into "_content/doc/go1.{version}.md" yet.
+	const (
+		// knownSubstringForPlaceholder is a substring used to identify when go1.N.md is still
+		// just a placeholder template like in CL 600179, without release note fragments merged in.
+		// We need some way of detecting whether the merge happened, and this will have to do.
+		knownSubstringForPlaceholder = "Eventually the release note fragments in doc/next will be merged"
+	)
+	mergedRelnoteFile := fmt.Sprintf("_content/doc/go1.%d.md", version)
+	b, err := t.Gerrit.ReadFile(ctx, "website", commit.String(), mergedRelnoteFile)
+	if err == nil && !bytes.Contains(b, []byte(knownSubstringForPlaceholder)) {
+		ctx.Printf("Release note fragments seem to be merged into %s in x/website, so refusing to run this task (and tasks that depend on it).", mergedRelnoteFile)
+		return NextRelnote{}, fmt.Errorf("%s already has merged fragments; the scope of this task is to merge fragments into that file only", mergedRelnoteFile)
+	} else if errors.Is(err, gerrit.ErrResourceNotExist) {
+		// OK. We'll be creating it below.
+	} else if err != nil {
+		return NextRelnote{}, err
+	}
+
 	// Collect all doc/next files to merge.
 	root, err := goRepo.CloneHash(commit)
 	if err != nil {
@@ -251,7 +282,7 @@ func (t ReleaseCycleTasks) MergeNextRelnoteAndAddToWebsite(ctx *wf.TaskContext,
 	if err != nil {
 		return NextRelnote{}, fmt.Errorf("relnote.Merge: %v", err)
 	}
-	mergedRelnote := fmt.Sprintf(`---
+	mergedRelnoteContent := fmt.Sprintf(`---
 title: Go 1.%d Release Notes
 template: false
 ---
@@ -269,9 +300,7 @@ template: false
 Using doc/next content as of %s (commit %s).
 
 For golang/go#%d.`, version, time.Now().Format(time.DateOnly), commit, releaseNotesIssue),
-	}, reviewers, map[string]string{
-		fmt.Sprintf("_content/doc/go1.%d.md", version): mergedRelnote,
-	})
+	}, reviewers, map[string]string{mergedRelnoteFile: mergedRelnoteContent})
 	if err != nil {
 		return NextRelnote{}, err
 	}