Discover next version by probing feed instead of hardcoded progression

Replace GetNextVersion (which hardcoded preview.7 → rc.1, rc.2 → ga)
with GetNextVersionFromFeed that queries the NuGet feed to find the
actual next milestone. This handles any number of previews or RCs
without assumptions about the release cadence.

When no newer version exists on the same major, the function probes
the next major version's feed automatically.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jeffhandley

release-notes/RunApiDiff.ps1

@@ -207,32 +207,80 @@ Function FindLatestApiDiff {
     Return ($entries | Sort-Object { $_.SortKey } | Select-Object -Last 1)
 }
 
-## Given a version milestone, return the next one in the progression
-## preview.1 → preview.2 → ... → preview.7 → rc.1 → rc.2 → ga → {next major}.0 preview.1
-Function GetNextVersion {
+## Probe the NuGet feed to find the next version after a given milestone
+Function GetNextVersionFromFeed {
     Param (
         [string] $majorMinor,
-        [string] $prereleaseLabel
+        [string] $prereleaseLabel,
+        [string] $feedUrl
     )
-    $parsed = ParsePrereleaseLabel $prereleaseLabel
-    $kind = $parsed.ReleaseKind
-    $number = [int]$parsed.PreviewRCNumber
 
-    If ($kind -eq "preview" -and $number -lt 7) {
-        Return @{ MajorMinor = $majorMinor; PrereleaseLabel = "preview.$($number + 1)" }
+    $currentParsed = ParsePrereleaseLabel $prereleaseLabel
+    $currentWeight = GetMilestoneSortWeight $currentParsed.ReleaseKind ([int]$currentParsed.PreviewRCNumber)
+
+    $serviceIndex = Invoke-RestMethod -Uri $feedUrl
+    $flatContainer = $serviceIndex.resources | Where-Object { $_.'@type' -match 'PackageBaseAddress' } | Select-Object -First 1
+    If (-not $flatContainer) { Return $null }
+
+    $baseUrl = $flatContainer.'@id'
+    $versionsUrl = "${baseUrl}microsoft.netcore.app.ref/index.json"
+
+    try {
+        $versionsResult = Invoke-RestMethod -Uri $versionsUrl
+    }
+    catch { Return $null }
+
+    If (-not $versionsResult.versions -or $versionsResult.versions.Count -eq 0) { Return $null }
+
+    # Find versions for the same MajorMinor that come after the current milestone
+    $candidates = @()
+    ForEach ($v in $versionsResult.versions) {
+        $parsed = $null
+        try { $parsed = ParseVersionString $v "probe" } catch { Continue }
+        If ($parsed.MajorMinor -ne $majorMinor) { Continue }
+
+        $milestoneParsed = ParsePrereleaseLabel $parsed.PrereleaseLabel
+        $weight = GetMilestoneSortWeight $milestoneParsed.ReleaseKind ([int]$milestoneParsed.PreviewRCNumber)
+        If ($weight -gt $currentWeight) {
+            $candidates += @{ MajorMinor = $parsed.MajorMinor; PrereleaseLabel = $parsed.PrereleaseLabel; Weight = $weight }
+        }
     }
-    If ($kind -eq "preview") {
-        Return @{ MajorMinor = $majorMinor; PrereleaseLabel = "rc.1" }
+
+    If ($candidates.Count -gt 0) {
+        Return ($candidates | Sort-Object { $_.Weight } | Select-Object -First 1)
     }
-    If ($kind -eq "rc" -and $number -lt 2) {
-        Return @{ MajorMinor = $majorMinor; PrereleaseLabel = "rc.$($number + 1)" }
+
+    # No newer milestone found on the same major — try the next major's feed
+    $nextMajor = [int]($majorMinor.Split(".")[0]) + 1
+    $nextMajorMinor = "$nextMajor.0"
+    $nextFeedUrl = "https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet${nextMajor}/nuget/v3/index.json"
+
+    Write-Color cyan "No newer milestone found for $majorMinor on feed. Probing next major feed for $nextMajorMinor..."
+
+    try {
+        $nextServiceIndex = Invoke-RestMethod -Uri $nextFeedUrl
+        $nextFlatContainer = $nextServiceIndex.resources | Where-Object { $_.'@type' -match 'PackageBaseAddress' } | Select-Object -First 1
+        If (-not $nextFlatContainer) { Return $null }
+
+        $nextBaseUrl = $nextFlatContainer.'@id'
+        $nextVersionsUrl = "${nextBaseUrl}microsoft.netcore.app.ref/index.json"
+        $nextVersionsResult = Invoke-RestMethod -Uri $nextVersionsUrl
+
+        If ($nextVersionsResult.versions -and $nextVersionsResult.versions.Count -gt 0) {
+            ForEach ($v in $nextVersionsResult.versions) {
+                $parsed = $null
+                try { $parsed = ParseVersionString $v "probe" } catch { Continue }
+                If ($parsed.MajorMinor -eq $nextMajorMinor) {
+                    Return @{ MajorMinor = $parsed.MajorMinor; PrereleaseLabel = $parsed.PrereleaseLabel }
+                }
+            }
+        }
     }
-    If ($kind -eq "rc") {
-        Return @{ MajorMinor = $majorMinor; PrereleaseLabel = "" }
+    catch {
+        Write-Color yellow "Could not probe next major feed: $_"
     }
-    # GA → next major preview.1
-    $major = [int]($majorMinor.Split(".")[0])
-    Return @{ MajorMinor = "$($major + 1).0"; PrereleaseLabel = "preview.1" }
+
+    Return $null
 }
 
 Function DiscoverVersionFromFeed {
@@ -950,11 +998,19 @@ If ([System.String]::IsNullOrWhiteSpace($CurrentMajorMinor) -and [System.String]
         $latestDesc = If ($latestApiDiff.PrereleaseLabel) { "$($latestApiDiff.MajorMinor)-$($latestApiDiff.PrereleaseLabel)" } Else { "$($latestApiDiff.MajorMinor) GA" }
         Write-Color cyan "Latest existing api-diff: $latestDesc"
 
-        $next = GetNextVersion $latestApiDiff.MajorMinor $latestApiDiff.PrereleaseLabel
-        $CurrentMajorMinor = $next.MajorMinor
-        $CurrentPrereleaseLabel = $next.PrereleaseLabel
-        $nextDesc = If ($CurrentPrereleaseLabel) { "$CurrentMajorMinor-$CurrentPrereleaseLabel" } Else { "$CurrentMajorMinor GA" }
-        Write-Color green "Inferred current version: $nextDesc"
+        # Probe the feed for the next version after the latest api-diff
+        $latestMajorVersion = $latestApiDiff.MajorMinor.Split(".")[0]
+        $probeFeedUrl = "https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet${latestMajorVersion}/nuget/v3/index.json"
+        $next = GetNextVersionFromFeed $latestApiDiff.MajorMinor $latestApiDiff.PrereleaseLabel $probeFeedUrl
+
+        If ($next) {
+            $CurrentMajorMinor = $next.MajorMinor
+            $CurrentPrereleaseLabel = $next.PrereleaseLabel
+            $nextDesc = If ($CurrentPrereleaseLabel) { "$CurrentMajorMinor-$CurrentPrereleaseLabel" } Else { "$CurrentMajorMinor GA" }
+            Write-Color green "Discovered next version from feed: $nextDesc"
+        } Else {
+            Write-Error "Could not discover the next version from feed '$probeFeedUrl' after $latestDesc. Specify -CurrentMajorMinor and -CurrentPrereleaseLabel explicitly." -ErrorAction Stop
+        }
 
         # Also infer previous from the latest api-diff if not explicitly provided
         If ([System.String]::IsNullOrWhiteSpace($PreviousMajorMinor) -and [System.String]::IsNullOrWhiteSpace($PreviousPrereleaseLabel) -and [System.String]::IsNullOrWhiteSpace($PreviousVersion)) {