fix(scripts/releaser): fix tag sorting and changelog blurb for older branches (#24798)

Fixes two bugs in the release tool.

## 1. RC tags chosen over release tags on release branches

`allSemverTags()` and `mergedSemverTags()` rely on `git tag
--sort=-v:refname` for ordering. Git's version sort treats pre-release
suffixes (e.g. `-rc.0`) as *greater* than the base release version,
which is the opposite of semver where `v2.32.0 > v2.32.0-rc.0`.

When the release branch code iterates the tag list looking for the first
matching `major.minor`, it finds the RC tag first, leading to incorrect
version suggestions (e.g. suggesting `v2.32.0` again instead of
`v2.32.1`).

**Fix:** Re-sort parsed tags using the existing `GreaterThan` method via
a new `sortVersionsDesc` helper.

## 2. Misleading mainline changelog blurb on ESR/older branch patches

When releasing a patch on an older branch (e.g. `release/2.29` for ESR),
the version is neither mainline nor stable. Declining the stable prompt
would always produce the mainline changelog note ("This is a mainline
Coder release..."), which is incorrect.

**Fix:** Only emit the mainline note when the version's minor matches
the current mainline series. For older branches the changelog omits the
note entirely.

> Generated by Coder Agents

scripts/releaser/release.go

@@ -631,9 +631,15 @@ func runRelease(ctx context.Context, inv *serpent.Invocation, executor ReleaseEx
 		fmt.Fprintln(&notes, "> [!NOTE]")
 		fmt.Fprintln(&notes, "> This is a **release candidate** (RC) for testing purposes. It is not recommended for production use. Please report any issues you encounter. Learn more about our [Release Schedule](https://coder.com/docs/install/releases).")
 	case "mainline":
-		fmt.Fprintln(&notes)
+		// Only show the mainline blurb when the version is
-		fmt.Fprintln(&notes, "> [!NOTE]")
+		// actually the current mainline series. Patches on
-		fmt.Fprintln(&notes, "> This is a mainline Coder release. We advise enterprise customers without a staging environment to install our [latest stable release](https://github.com/coder/coder/releases/latest) while we refine this version. Learn more about our [Release Schedule](https://coder.com/docs/install/releases).")
+		// older branches (e.g. ESR) are neither mainline nor
+		// stable, so we omit the note entirely.
+		if latestMainline != nil && newVersion.Minor == latestMainline.Minor {
+			fmt.Fprintln(&notes)
+			fmt.Fprintln(&notes, "> [!NOTE]")
+			fmt.Fprintln(&notes, "> This is a mainline Coder release. We advise enterprise customers without a staging environment to install our [latest stable release](https://github.com/coder/coder/releases/latest) while we refine this version. Learn more about our [Release Schedule](https://coder.com/docs/install/releases).")
+		}
 	}
 
 	hasContent := false

scripts/releaser/version.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"regexp"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -85,6 +86,17 @@ func (v version) Equal(b version) bool {
 	return v.Major == b.Major && v.Minor == b.Minor && v.Patch == b.Patch && v.Pre == b.Pre
 }
 
+// sortVersionsDesc sorts a slice of versions in descending order
+// using semver-correct comparison. This is necessary because git's
+// --sort=-v:refname treats pre-release suffixes (e.g. -rc.0) as
+// greater than the release version, which is the opposite of semver
+// where v2.32.0 > v2.32.0-rc.0.
+func sortVersionsDesc(tags []version) {
+	sort.Slice(tags, func(i, j int) bool {
+		return tags[i].GreaterThan(tags[j])
+	})
+}
+
 // allSemverTags returns all semver tags sorted descending.
 func allSemverTags() ([]version, error) {
 	out, err := gitOutput("tag", "--sort=-v:refname")
@@ -100,6 +112,7 @@ func allSemverTags() ([]version, error) {
 			tags = append(tags, v)
 		}
 	}
+	sortVersionsDesc(tags)
 	return tags, nil
 }
 
@@ -119,5 +132,6 @@ func mergedSemverTags() ([]version, error) {
 			tags = append(tags, v)
 		}
 	}
+	sortVersionsDesc(tags)
 	return tags, nil
 }

scripts/releaser/version_test.go

@@ -165,3 +165,76 @@ func TestVersionEqual(t *testing.T) {
 		})
 	}
 }
+
+func TestSortVersionsDesc(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		input []version
+		want  []version
+	}{
+		{
+			// This is the exact scenario that triggered the bug:
+			// git's --sort=-v:refname places v2.32.0-rc.0 before
+			// v2.32.0, but semver says v2.32.0 > v2.32.0-rc.0.
+			name: "release_sorts_before_rc",
+			input: []version{
+				{2, 32, 0, "rc.0"},
+				{2, 32, 0, ""},
+				{2, 31, 2, ""},
+			},
+			want: []version{
+				{2, 32, 0, ""},
+				{2, 32, 0, "rc.0"},
+				{2, 31, 2, ""},
+			},
+		},
+		{
+			name: "multiple_rcs_and_releases",
+			input: []version{
+				{2, 33, 0, "rc.1"},
+				{2, 33, 0, "rc.0"},
+				{2, 32, 0, "rc.0"},
+				{2, 32, 0, ""},
+				{2, 32, 1, ""},
+				{2, 31, 0, ""},
+			},
+			want: []version{
+				{2, 33, 0, "rc.1"},
+				{2, 33, 0, "rc.0"},
+				{2, 32, 1, ""},
+				{2, 32, 0, ""},
+				{2, 32, 0, "rc.0"},
+				{2, 31, 0, ""},
+			},
+		},
+		{
+			name:  "already_sorted",
+			input: []version{{3, 0, 0, ""}, {2, 0, 0, ""}, {1, 0, 0, ""}},
+			want:  []version{{3, 0, 0, ""}, {2, 0, 0, ""}, {1, 0, 0, ""}},
+		},
+		{
+			name:  "empty",
+			input: []version{},
+			want:  []version{},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			got := make([]version, len(tt.input))
+			copy(got, tt.input)
+			sortVersionsDesc(got)
+			if len(got) != len(tt.want) {
+				t.Fatalf("sortVersionsDesc() returned %d elements, want %d", len(got), len(tt.want))
+			}
+			for i := range got {
+				if !got[i].Equal(tt.want[i]) {
+					t.Fatalf("sortVersionsDesc()[%d] = %s, want %s\n  full result: %v", i, got[i], tt.want[i], got)
+				}
+			}
+		})
+	}
+}