Reduce allocations for cached command lookups

Engine/CommandInfoCache.cs

@@ -69,6 +69,19 @@ public CommandInfo GetCommandInfo(string commandName, CommandTypes? commandTypes
             {
                 return GetCommandInfoInternal(commandName, commandTypes);
             }
+
+            if (_commandInfoCache.TryGetValue(key, out Lazy<CommandInfo> cachedCommand))
+            {
+                return cachedCommand.Value;
+            }
+
+            return AddCommandInfo(key, commandName, commandTypes);
+        }
+
+        private CommandInfo AddCommandInfo(CommandLookupKey key, string commandName, CommandTypes? commandTypes)
+        {
+            // Keep the closure and Lazy allocation off the cache-hit path. Concurrent misses
+            // still share the winning Lazy so command discovery runs once for each key.
             // Atomically either use PowerShell to query a command info object, or fetch it from the cache
             return _commandInfoCache.GetOrAdd(key, new Lazy<CommandInfo>(() => GetCommandInfoInternal(commandName, commandTypes))).Value;
         }
@@ -146,7 +159,7 @@ public override int GetHashCode()
                 unchecked
                 {
                     int hash = 17;
-                    hash = hash * 31 + Name.ToUpperInvariant().GetHashCode();
+                    hash = hash * 31 + StringComparer.OrdinalIgnoreCase.GetHashCode(Name);
                     hash = hash * 31 + CommandTypes.GetHashCode();
                     return hash;
                 }

Tests/Engine/CommandInfoCache.tests.ps1

@@ -0,0 +1,42 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+Describe 'CommandInfoCache' {
+    BeforeEach {
+        $cacheType = [Microsoft.Windows.PowerShell.ScriptAnalyzer.Helper].Assembly.GetType(
+            'Microsoft.Windows.PowerShell.ScriptAnalyzer.CommandInfoCache', $true)
+        $cache = [Activator]::CreateInstance($cacheType)
+    }
+
+    AfterEach {
+        $cache.Dispose()
+    }
+
+    It 'Returns the cached command for differently cased names and equivalent command types' {
+        $command = $cache.GetCommandInfo('Get-Item', $null, $false)
+        $command | Should -Not -BeNullOrEmpty
+        $cached = $cache.GetCommandInfo('gET-iTEM', [System.Management.Automation.CommandTypes]::All, $false)
+        [object]::ReferenceEquals($command, $cached) | Should -BeTrue
+    }
+
+    It 'Keeps command-type filters separate from an existing cache entry' {
+        $cache.GetCommandInfo('Get-Item', [System.Management.Automation.CommandTypes]::Function, $false) |
+            Should -BeNullOrEmpty
+        $command = $cache.GetCommandInfo('Get-Item', [System.Management.Automation.CommandTypes]::Cmdlet, $false)
+        $command.CommandType | Should -Be ([System.Management.Automation.CommandTypes]::Cmdlet)
+        $cache.GetCommandInfo('GET-ITEM', [System.Management.Automation.CommandTypes]::Function, $false) |
+            Should -BeNullOrEmpty
+    }
+
+    It 'Uses ordinal case-insensitive lookup independently of the current culture' {
+        $originalCulture = [System.Threading.Thread]::CurrentThread.CurrentCulture
+        try {
+            $command = $cache.GetCommandInfo('Get-Item', $null, $false)
+            [System.Threading.Thread]::CurrentThread.CurrentCulture = [System.Globalization.CultureInfo]::GetCultureInfo('tr-TR')
+            $cached = $cache.GetCommandInfo('get-item', $null, $false)
+            [object]::ReferenceEquals($command, $cached) | Should -BeTrue
+        } finally {
+            [System.Threading.Thread]::CurrentThread.CurrentCulture = $originalCulture
+        }
+    }
+}