From 9daad20cf979b8f1480af1a59ae758c9ba75e6a5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Jare=C5=A1?= <me@jakubjares.com>
Date: Sun, 19 Jul 2026 12:08:18 +0200
Subject: [PATCH] Skip unused work in discovery post-processing and output
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The WriteScreen plugin flattened the whole discovered tree with View-Flat
on DiscoveryEnd, but the result is only read when Run.SkipRun is set or
verbosity is Detailed/Diagnostic, in the default run it was computed and
thrown away. It is now computed only when one of those consumers can read
it.

The RSpec decoration walk (Add-RSpecTestObjectProperties per test) and
Remove-RSpecNonPublicProperties used Fold-Container/Fold-Run, which pay a
scriptblock dispatch per item and an advanced-function recursion per block.
Both are now direct recursive loops that visit the same items in the same
pre-order.

Format-Nicely2 called Is-DecimalNumber, Is-ScriptBlock, Is-Collection and
Is-Value helpers on every formatted value, on the dispatch path used for
every <template> name expansion. The type checks are inlined, the helpers
stay defined for other callers.

🤖
---
 src/Format2.ps1          | 14 +++++--
 src/Main.ps1             |  4 +-
 src/Pester.RSpec.ps1     | 88 +++++++++++++++++++---------------------
 src/functions/Output.ps1 |  7 +++-
 4 files changed, 59 insertions(+), 54 deletions(-)

diff --git a/src/Format2.ps1 b/src/Format2.ps1
index 64df841ea..35bd93d40 100644
--- a/src/Format2.ps1
+++ b/src/Format2.ps1
@@ -122,11 +122,13 @@ function Format-Nicely2 ($Value, [switch]$Pretty, [int]$Depth = 0) {
         return Format-Type2 -Value $Value
     }
 
-    if (Is-DecimalNumber -Value $Value) {
+    # Inlined Is-DecimalNumber / Is-ScriptBlock to avoid a function call per formatted value on this
+    # hot dispatch path (used for every <template> name expansion). The helpers stay defined for other callers.
+    if ($Value -is [float] -or $Value -is [single] -or $Value -is [double] -or $Value -is [decimal]) {
         return Format-Number2 -Value $Value
     }
 
-    if (Is-ScriptBlock -Value $Value) {
+    if ($Value -is [ScriptBlock]) {
         return Format-ScriptBlock2 -Value $Value
     }
 
@@ -142,11 +144,15 @@ function Format-Nicely2 ($Value, [switch]$Pretty, [int]$Depth = 0) {
         return Get-ShortType2 -Value $Value
     }
 
-    if (Is-Collection -Value $Value) {
+    # Inlined Is-Collection (same LanguagePrimitives::GetEnumerator check the helper runs).
+    if ($null -ne [System.Management.Automation.LanguagePrimitives]::GetEnumerator($Value)) {
         return Format-Collection2 -Value $Value -Pretty:$Pretty -Depth $Depth
     }
 
-    if (Is-Value -Value $Value) {
+    # Inlined Is-Value. The helper's leading `$Value = $($Value)` (which unwraps single-element and empty
+    # collections) is intentionally dropped: any collection was already handled by the Is-Collection branch
+    # above, so here $Value is never a collection and the unwrap is a no-op.
+    if ($Value -is [ValueType] -or $Value -is [string] -or $Value -is [scriptblock]) {
         return $Value
     }
 
diff --git a/src/Main.ps1 b/src/Main.ps1
index cba6dad83..9ecd6ddf9 100644
--- a/src/Main.ps1
+++ b/src/Main.ps1
@@ -853,7 +853,7 @@ function Invoke-Pester {
                     }
 
                     foreach ($c in $rspecResult.Containers) {
-                        Fold-Container -Container $c  -OnTest { param($t) Add-RSpecTestObjectProperties $t }
+                        Add-RSpecTestObjectPropertiesToContainer $c
                         $foldedContainers.Add($c)
                     }
                 }
@@ -931,7 +931,7 @@ function Invoke-Pester {
                 }
 
                 foreach ($c in $rspecContainers) {
-                    Fold-Container -Container $c  -OnTest { param($t) Add-RSpecTestObjectProperties $t }
+                    Add-RSpecTestObjectPropertiesToContainer $c
                 }
             }
 
diff --git a/src/Pester.RSpec.ps1 b/src/Pester.RSpec.ps1
index da2ff4305..e0e30fbb5 100644
--- a/src/Pester.RSpec.ps1
+++ b/src/Pester.RSpec.ps1
@@ -203,6 +203,24 @@ function Add-RSpecBlockObjectProperties ($BlockObject) {
     }
 }
 
+function Add-RSpecTestObjectPropertiesToContainer ($Container) {
+    # Direct walk over the container tree instead of Fold-Container. It visits every test in the
+    # same pre-order (tests of a block before its child blocks), but without the fold's per-item
+    # scriptblock dispatch and per-block advanced-function recursion.
+    foreach ($b in $Container.Blocks) {
+        Add-RSpecTestObjectPropertiesToBlock $b
+    }
+}
+
+function Add-RSpecTestObjectPropertiesToBlock ($Block) {
+    foreach ($t in $Block.Tests) {
+        Add-RSpecTestObjectProperties $t
+    }
+    foreach ($b in $Block.Blocks) {
+        Add-RSpecTestObjectPropertiesToBlock $b
+    }
+}
+
 function PostProcess-RspecTestRun ($TestRun, [switch] $Parallel, [TimeSpan] $RunDuration) {
     $discoveryOnly = $PesterPreference.Run.SkipRun.Value
 
@@ -507,56 +525,32 @@ function Remove-RSpecNonPublicProperties ($run) {
     #     'Duration'
     # )
 
-    Fold-Run $run -OnRun {
-        param($i)
-        # $ps = $i.PsObject.Properties.Name
-        # foreach ($p in $ps) {
-        #     if ($p -like 'Plugin*') {
-        #         $i.PsObject.Properties.Remove($p)
-        #     }
-        # }
+    # Direct walk over the run tree instead of Fold-Run; same visit of every block and test,
+    # without the fold's per-item scriptblock dispatch. Containers need no cleanup.
+    foreach ($r in $run) {
+        $r.PluginConfiguration = $null
+        $r.PluginData = $null
+        $r.Plugins = $null
 
-        $i.PluginConfiguration = $null
-        $i.PluginData = $null
-        $i.Plugins = $null
+        foreach ($c in $r.Containers) {
+            foreach ($b in $c.Blocks) {
+                Remove-RSpecNonPublicPropertiesFromBlock $b
+            }
+        }
+    }
+}
 
-    } -OnContainer {
-        param($i)
-        # $ps = $i.PsObject.Properties.Name
-        # foreach ($p in $ps) {
-        #     if ($p -like 'Own*') {
-        #         $i.PsObject.Properties.Remove($p)
-        #     }
-        # }
-
-        # $i.FrameworkData = $null
-        # $i.PluginConfiguration = $null
-        # $i.PluginData = $null
-        # $i.Plugins = $null
+function Remove-RSpecNonPublicPropertiesFromBlock ($Block) {
+    $Block.FrameworkData = $null
+    $Block.PluginData = $null
 
-    } -OnBlock {
-        param($i)
-        # $ps = $i.PsObject.Properties.Name
-        # foreach ($p in $ps) {
-        #     if ($p -eq 'FrameworkData' -or $p -like 'Own*' -or $p -like 'Plugin*') {
-        #         $i.PsObject.Properties.Remove($p)
-        #     }
-        # }
-
-        $i.FrameworkData = $null
-        $i.PluginData = $null
-
-    } -OnTest {
-        param($i)
-        # $ps = $i.PsObject.Properties.Name
-        # foreach ($p in $ps) {
-        #     if ($p -eq 'FrameworkData' -or $p -like 'Plugin*') {
-        #         $i.PsObject.Properties.Remove($p)
-        #     }
-        # }
-
-        $i.FrameworkData = $null
-        $i.PluginData = $null
+    foreach ($t in $Block.Tests) {
+        $t.FrameworkData = $null
+        $t.PluginData = $null
+    }
+
+    foreach ($b in $Block.Blocks) {
+        Remove-RSpecNonPublicPropertiesFromBlock $b
     }
 }
 
diff --git a/src/functions/Output.ps1 b/src/functions/Output.ps1
index 8f7123643..6c809c9b1 100644
--- a/src/functions/Output.ps1
+++ b/src/functions/Output.ps1
@@ -555,7 +555,12 @@ function Get-WriteScreenPlugin ($Verbosity) {
     $p.DiscoveryEnd = {
         param ($Context)
 
-        $discoveredTests = @(View-Flat -Block $Context.BlockContainers)
+        # flattening the tree costs time proportional to the number of discovered tests, and the
+        # result is only read by the two guarded blocks below, so skip it in the default run
+        # (Normal verbosity, not discovery-only) where neither guard can be entered
+        $discoveredTests = if ($PesterPreference.Run.SkipRun.Value -or $PesterPreference.Output.Verbosity.Value -in 'Detailed', 'Diagnostic') {
+            @(View-Flat -Block $Context.BlockContainers)
+        }
 
         if ($PesterPreference.Run.SkipRun.Value) {
             # Only announce the discovery result on screen when we are not going to run