Reject a device category that selects the reproduction out

The published device selector is TestFilter=Category=Issue<N>, and
DeviceTestSharedHelpers.GetExcludedTestCategories implements that by
subtraction: it lists the public static string fields of TestCategory,
removes the requested one, and excludes everything left. "Issue<N>" is
deliberately not a TestCategory field, so the removal is a no-op and every
conventional category ends up excluded -- including the one the test itself
declares. The selector then selects the test out rather than in.

The authoring guidance asked for exactly that shape, telling the agent to
add [Category("Issue<N>")] "in addition to any conventional TestCategory".

Reviewers measured the consequence twice: an Android reproduction reported
576 discovered / 3 passed / 573 ignored, and a Mac Catalyst one executed
zero tests. Deleting only the broad category made each exact test run.

Windows is exempt and stays exempt: its runner filters by discovered traits,
so "Issue<N>" is a real category there.

Corrects the guidance, rejects the shape in both the authoring guards and
the publishing gate, and fixes the doc comment that asserted the opposite.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 735ac9a2-7bec-4baa-ad19-c298e5bc795a

Author: Copilot CI

.github/scripts/Replicate-Issue.Tests.ps1

@@ -13595,3 +13595,94 @@ Describe 'A CS0104 ambiguity is resolved, not re-described' {
     }
 }
 
+
+Describe 'An issue-keyed device category is the only category on skip-filtered platforms' {
+    # DeviceTestSharedHelpers.GetExcludedTestCategories implements
+    # "Category=X" by subtraction over the public static string fields of
+    # TestCategory. "Issue<N>" is not one of those fields, so the removal is a
+    # no-op and every conventional category is excluded -- which excludes any
+    # test that also declares one. Measured on PR 533 (Android, Shape +
+    # Issue31330: 576 discovered, 3 passed, 573 ignored) and PR 515
+    # (Mac Catalyst, Accessibility + Issue37140: zero tests executed).
+
+    It 'reports the conventional category that hides the test on <platform>' -ForEach @(
+        @{ platform = 'android' }
+        @{ platform = 'ios' }
+        @{ platform = 'catalyst' }
+    ) {
+        $source = "public class T`n{`n`t[Category(TestCategory.Shape)]`n`t[Category(`"Issue31330`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 31330 -Platform $platform |
+            Should -Be 'TestCategory.Shape'
+    }
+
+    It 'reports a broad category written as a string literal' {
+        # PR 515's shape, verbatim: Accessibility alongside Issue37140.
+        $source = "public class T`n{`n`t[Category(`"Accessibility`")]`n`t[Category(`"Issue37140`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 37140 -Platform 'catalyst' |
+            Should -Be '"Accessibility"'
+    }
+
+    It 'reports a conventional category combined into one attribute' {
+        # The exact shape the old guidance recommended.
+        $source = "public class T`n{`n`t[Category(TestCategory.Entry, `"Issue37275`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 37275 -Platform 'android' |
+            Should -Be 'TestCategory.Entry'
+    }
+
+    It 'accepts the issue-keyed category on its own' {
+        $source = "public class T`n{`n`t[Category(`"Issue31330`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 31330 -Platform 'android' |
+            Should -BeNullOrEmpty
+    }
+
+    It 'exempts windows, which selects from discovered traits' {
+        # ControlsHeadlessTestRunner collects tc.Traits["Category"], so
+        # "Issue31330" is a real category there. PR 525 selected its single
+        # Windows test correctly with a second category present.
+        $source = "public class T`n{`n`t[Category(TestCategory.Shape)]`n`t[Category(`"Issue31330`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 31330 -Platform 'windows' |
+            Should -BeNullOrEmpty
+    }
+
+    It 'ignores a commented-out conventional category' {
+        $source = "public class T`n{`n`t// [Category(TestCategory.Shape)]`n`t[Category(`"Issue31330`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 31330 -Platform 'android' |
+            Should -BeNullOrEmpty
+    }
+
+    It 'ignores a conventional category inside a block comment' {
+        # The line anchor alone cannot reject this one: the attribute does
+        # start its own line, so only comment stripping removes it.
+        $source = "public class T`n{`n/*`n[Category(TestCategory.Shape)]`n*/`n`t[Category(`"Issue31330`")]`n`tpublic void M() { }`n}"
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content $source -Path 'a.cs' -Issue 31330 -Platform 'android' |
+            Should -BeNullOrEmpty
+    }
+
+    It 'says nothing about empty content' {
+        Assert-ReplicationDeviceCategoryIsExclusive `
+            -Content '' -Path 'a.cs' -Issue 31330 -Platform 'android' |
+            Should -BeNullOrEmpty
+    }
+
+    It 'is wired into the device-test authoring guards' {
+        $orchestrator = Get-Content -LiteralPath (
+            Join-Path $PSScriptRoot 'Replicate-Issue.ps1') -Raw
+        $orchestrator | Should -Match 'Assert-ReplicationDeviceCategoryIsExclusive'
+        # The remedy has to name the offending category, or the author cannot
+        # act on it without guessing which attribute to delete.
+        $orchestrator | Should -Match 'Declare the issue-keyed category on its'
+    }
+
+    It 'tells the author to keep the category alone' {
+        $orchestrator = Get-Content -LiteralPath (
+            Join-Path $PSScriptRoot 'Replicate-Issue.ps1') -Raw
+        $orchestrator | Should -Match 'that must be the ONLY category the test carries'
+    }
+}

.github/scripts/Replicate-Issue.ps1

@@ -3703,6 +3703,24 @@ function Assert-GeneratedTestContent {
                                 -Issue $Issue) {
                             $deviceTestIsSelectable = $true
                         }
+                        $conflict = Assert-ReplicationDeviceCategoryIsExclusive `
+                            -Content $content `
+                            -Path $file `
+                            -Issue $Issue `
+                            -Platform $TargetPlatform
+                        if ($conflict) {
+                            $conflictMessage = (
+                                "Generated device test '$file' declares [Category($conflict)] " +
+                                "alongside [Category(`"Issue$Issue`")]. On $TargetPlatform the " +
+                                'runner implements "Category=X" by excluding every other ' +
+                                'TestCategory field, and "Issue' + $Issue + '" is not one of ' +
+                                "them, so [Category($conflict)] lands in the excluded list and " +
+                                'the test is skipped. Declare the issue-keyed category on its ' +
+                                'own so the published selector selects it.')
+                            if (-not $guardFailures.Contains($conflictMessage)) {
+                                $guardFailures.Add($conflictMessage)
+                            }
+                        }
                     } catch {
                         $message = $_.Exception.Message
                         if (-not $guardFailures.Contains($message)) { $guardFailures.Add($message) }
@@ -5963,7 +5981,7 @@ If the issue requests a new public event, property, method, or other API that do
 Use testFilter "Maui$IssueNumber" only for XAML; otherwise use "Issue$IssueNumber".
 Never assert an environment precondition. A test that calls Assert.True(OperatingSystem.IsIOSVersionAtLeast(26), ...) turns red on every device below that floor before its oracle runs, so the failure reports the lane rather than the defect and survives a complete product fix. When the reported behavior needs an OS floor, skip instead: "if (!OperatingSystem.IsIOSVersionAtLeast(26)) return;" -- the shape this repository uses at 49 sites. The same applies to throwing or Assert.Fail from an unmet version gate.
 
-A device test must also declare [Category("Issue$IssueNumber")] on its test class, in addition to any conventional TestCategory it already carries. CategoryAttribute takes params string[] and allows multiples, so this adds a category without editing the shared TestCategory file. The stock device-test runner honours only "Category=X" and "SkipCategories=X,Y", so without this category the published selector cannot isolate the reproduction and the whole suite runs instead.
+A device test must also declare [Category("Issue$IssueNumber")] on its test class, and on android, ios and catalyst that must be the ONLY category the test carries. Do not add a conventional TestCategory next to it. The stock device-test runner honours only "Category=X" and "SkipCategories=X,Y", and it implements "Category=X" by subtraction: it lists the public static string fields of TestCategory, removes X, and excludes every one that remains. "Issue$IssueNumber" is not a TestCategory field, so removing it removes nothing and every conventional category ends up excluded -- a test that also declares [Category(TestCategory.Shape)] then carries an excluded category and is skipped. Reviewers measured this twice: an Android reproduction reported 576 discovered / 3 passed / 573 ignored, and a Mac Catalyst one executed zero tests; deleting only the broad category made each exact test run. Windows selects from discovered traits instead, so a second category is harmless there, but keep the issue-keyed category alone on every platform for one publishable selector. Without this category the published selector cannot isolate the reproduction and the whole suite runs instead.
 List 1-10 exact new repository-relative .cs or .xaml files. Every filename must contain "$IssueNumber", every parent directory must already exist, and every path must be under one of these roots:
 $approvedRoots
 $existingIssueGuidance

.github/scripts/shared/Assert-ReplicationTestGuard.ps1

@@ -2217,9 +2217,11 @@ function Assert-ReplicationDeviceTestIsSelectable {
         sibling from muddying the verdict.
 
         CategoryAttribute takes params string[] and allows multiples, so an
-        issue-keyed category sits alongside the conventional
+        issue-keyed category can sit alongside the conventional
         [Category(TestCategory.Entry)] without touching TestCategory -- which
-        matters, because editing that shared file is not add-only.
+        matters, because editing that shared file is not add-only. On the
+        skip-filtered platforms that second category makes the test
+        unselectable; Assert-ReplicationDeviceCategoryIsExclusive rejects it.
 
         With [Category("Issue<N>")] present, the token names a real discovered
         category, so the selector published in the pull request is one the
@@ -2242,6 +2244,63 @@ function Assert-ReplicationDeviceTestIsSelectable {
     return [bool]([regex]::IsMatch($Content, $pattern))
 }
 
+function Assert-ReplicationDeviceCategoryIsExclusive {
+    <#
+        .SYNOPSIS
+        Reports a conventional category that makes an issue-keyed device test
+        unselectable on the skip-filtered platforms.
+
+        .DESCRIPTION
+        DeviceTestSharedHelpers.GetExcludedTestCategories implements
+        "TestFilter=Category=X" by *subtraction*: it lists the public static
+        string fields of TestCategory, removes X, and excludes everything that
+        is left. "Issue<N>" is deliberately not a TestCategory field, so
+        removing it removes nothing and every conventional category ends up in
+        the excluded list. A test that also declares [Category(TestCategory.Shape)]
+        therefore carries an excluded category and is skipped -- the published
+        selector selects it out rather than in.
+
+        Reviewers measured exactly this twice: PR 533 (Android, Shape +
+        Issue31330) reported 576 discovered / 3 passed / 573 ignored, and
+        PR 515 (Mac Catalyst, Accessibility + Issue37140) executed zero tests.
+        In both cases removing only the broad category made the exact test run.
+
+        Windows is exempt. Its runner filters by *discovered* traits
+        (ControlsHeadlessTestRunner collects tc.Traits["Category"]), so
+        "Issue<N>" is a real category there and a second one is harmless --
+        which is why PR 525 selected its single Windows test correctly.
+
+        Returns the offending category argument, or an empty string when the
+        issue-keyed category is the only one.
+    #>
+    param(
+        [Parameter(Mandatory = $true)][AllowEmptyString()][string]$Content,
+        [Parameter(Mandatory = $true)][string]$Path,
+        [Parameter(Mandatory = $true)][int]$Issue,
+        [Parameter(Mandatory = $true)][AllowEmptyString()][string]$Platform
+    )
+
+    if ([string]::IsNullOrWhiteSpace($Content)) { return '' }
+    if ($Platform -notin @('android', 'ios', 'catalyst')) { return '' }
+
+    # A commented-out attribute declares nothing.
+    $source = Get-ReplicationCommentFreeText -Text $Content -Path $Path
+    $token = '"Issue' + $Issue + '"'
+
+    foreach ($match in [regex]::Matches(
+            $source,
+            '(?m)^\s*\[\s*(?:(?:[A-Za-z_]\w*)\.)*Category\s*\(([^)]*)\)')) {
+        foreach ($argument in ($match.Groups[1].Value -split ',')) {
+            $trimmed = $argument.Trim()
+            if (-not $trimmed) { continue }
+            if ($trimmed -ceq $token) { continue }
+            return $trimmed
+        }
+    }
+
+    return ''
+}
+
 function Get-ReplicationEnvironmentCapabilityPattern {
     # Calls that report which lane the test landed in, not what the product did.
     return '(?:OperatingSystem\.Is[A-Za-z]*VersionAtLeast|UIDevice\.CurrentDevice\.CheckSystemVersion|Build\.VERSION\.SdkInt)'

.github/scripts/shared/Validate-ReplicationCandidate.ps1

@@ -2056,6 +2056,30 @@ function Assert-ReplicationCandidateSources {
             ) {
                 $deviceTestIsSelectable = $true
             }
+            if ($Manifest.TestType -ceq 'DeviceTest') {
+                # A second category does not merely dilute the selector, it
+                # inverts it: "Category=Issue<N>" is implemented by excluding
+                # every other TestCategory field, so the conventional category
+                # this test also carries lands in the excluded list and the
+                # test is skipped. Publishing that selector ships a
+                # reproduction nobody can run.
+                $categoryConflict = Assert-ReplicationDeviceCategoryIsExclusive `
+                    -Content $file.Content `
+                    -Path $file.Path `
+                    -Issue ([int]$Manifest.IssueNumber) `
+                    -Platform ([string]$Manifest.Platform)
+                if ($categoryConflict) {
+                    throw (
+                        "Candidate device test '$($file.Path)' declares " +
+                        "[Category($categoryConflict)] alongside " +
+                        "[Category(`"Issue$($Manifest.IssueNumber)`")]. On " +
+                        "$($Manifest.Platform) the runner implements " +
+                        '"Category=X" by excluding every other TestCategory ' +
+                        'field, so that conventional category is excluded and ' +
+                        'the test is skipped. Declare the issue-keyed ' +
+                        'category on its own.')
+                }
+            }
         }
         Assert-SourceTextIsSafe `
             -Content $file.Content `