PowerShell · iSazonov · Oct 18, 2018 · Oct 13, 2018 · Oct 13, 2018 · Oct 15, 2018
diff --git a/src/System.Management.Automation/engine/ErrorPackage.cs b/src/System.Management.Automation/engine/ErrorPackage.cs
@@ -1670,6 +1670,19 @@ public override string ToString()
 
     } // class ErrorRecord
 
+    /// <summary>
+    /// Dummy generic class for type inference purposes on typed catch blocks.
+    /// </summary>
+    /// <typeparam name="TException">Anything that inherits Exception.</typeparam>
+    internal class ErrorRecord<TException> : ErrorRecord where TException : Exception
+    {
+        public new TException Exception { get; }
+
+        public ErrorRecord(Exception exception, string errorId, ErrorCategory errorCategory, object targetObject) : base(exception, errorId, errorCategory, targetObject)
+        {
+        }
+    }
+
     /// <summary>
     /// Implemented by exception classes which contain additional
     /// <see cref="System.Management.Automation.ErrorRecord"/>

@@ -1803,7 +1803,7 @@ private void InferTypeFrom(VariableExpressionAst variableExpressionAst, List<PST
                 // $_ is special, see if we're used in a script block in some pipeline.
                 while (parent != null)
                 {
-                    if (parent is ScriptBlockExpressionAst)
+                    if (parent is ScriptBlockExpressionAst || parent is CatchClauseAst)
                     {
                         break;
                     }
@@ -1832,6 +1832,27 @@ private void InferTypeFrom(VariableExpressionAst variableExpressionAst, List<PST
                         parent = parent.Parent;
                     }
 
+                    if (parent is CatchClauseAst catchBlock)
+                    {
+                        if (catchBlock.CatchTypes.Count > 0)
+                        {
+                            foreach (TypeConstraintAst catchType in catchBlock.CatchTypes)
+                            {
+                                Type exceptionType = catchType.TypeName.GetReflectionType();
+                                if (exceptionType != null && typeof(Exception).IsAssignableFrom(exceptionType))
+                                {
+                                    inferredTypes.Add(new PSTypeName(typeof(ErrorRecord<>).MakeGenericType(exceptionType)));
+                                }
+                            }
+                        }
+                        else
+                        {
+                            inferredTypes.Add(new PSTypeName(typeof(ErrorRecord)));
+                        }
+
+                        return;
+                    }
+
                     if (parent.Parent is CommandAst commandAst)
                     {
                         // We found a command, see if there is a previous command in the pipeline.

diff --git a/test/powershell/engine/Api/TypeInference.Tests.ps1 b/test/powershell/engine/Api/TypeInference.Tests.ps1
@@ -926,6 +926,90 @@ Describe "Type inference Tests" -tags "CI" {
         $res.Name | Should -Be System.Int32
     }
 
+    It 'Infers type of variable $_ in catch block' {
+        $variableAst = { try {} catch { $_ } }.Ast.Find({ param($a) $a -is [System.Management.Automation.Language.VariableExpressionAst] }, $true)
+        $res = [AstTypeInference]::InferTypeOf($variableAst)
+
+        $res | Should -HaveCount 1
+        $res.Name | Should -Be System.Management.Automation.ErrorRecord
+    }
+
+    It 'Infers type of untyped $_.Exception in catch block' {
+        $memberAst = { try {} catch { $_.Exception } }.Ast.Find({ param($a) $a -is [System.Management.Automation.Language.MemberExpressionAst] }, $true)
+        $res = [AstTypeInference]::InferTypeOf($memberAst)
+
+        $res | Should -HaveCount 1
+        $res.Name | Should -Be System.Exception
+    }
+
+    $catchClauseTypes = @(
+        @{ Type = 'System.ArgumentException' }
+        @{ Type = 'System.ArgumentNullException' }
+        @{ Type = 'System.ArgumentOutOfRangeException' }
+        @{ Type = 'System.Collections.Generic.KeyNotFoundException' }
+        @{ Type = 'System.DivideByZeroException' }
+        @{ Type = 'System.FormatException' }
+        @{ Type = 'System.IndexOutOfRangeException' }
+        @{ Type = 'System.InvalidOperationException' }
+        @{ Type = 'System.IO.DirectoryNotFoundException' }
+        @{ Type = 'System.IO.DriveNotFoundException' }
+        @{ Type = 'System.IO.FileNotFoundException' }
+        @{ Type = 'System.IO.PathTooLongException' }
+        @{ Type = 'System.Management.Automation.CommandNotFoundException' }
+        @{ Type = 'System.Management.Automation.JobFailedException' }
+        @{ Type = 'System.Management.Automation.RuntimeException' }
+        @{ Type = 'System.Management.Automation.ValidationMetadataException' }
+        @{ Type = 'System.NotImplementedException' }
+        @{ Type = 'System.NotSupportedException' }
+        @{ Type = 'System.ObjectDisposedException' }
+        @{ Type = 'System.OverflowException' }
+        @{ Type = 'System.PlatformNotSupportedException' }
+        @{ Type = 'System.RankException' }
+        @{ Type = 'System.TimeoutException' }
+        @{ Type = 'System.UriFormatException' }
+    )
+
+    It 'Infers type of $_.Exception in [<Type>] typed catch block' -TestCases $catchClauseTypes {
+        param($Type)
+
+        $memberAst = [scriptblock]::Create("try {} catch [$Type] { `$_.Exception }").Ast.Find(
+            { param($a) $a -is [System.Management.Automation.Language.MemberExpressionAst] },
+            $true
+        )
+        $res = [AstTypeInference]::InferTypeOf($memberAst)
+
+        $res | Should -HaveCount 1
+        $res.Name | Should -Be $Type
+    }
+
+    It 'Infers possible types of $_.Exception in multi-typed catch block' {
+        $memberAst = { try {} catch [System.ArgumentException], [System.NotImplementedException] { $_.Exception } }.Ast.Find(
+            { param($a) $a -is [System.Management.Automation.Language.MemberExpressionAst] },
+            $true
+        )
+        $res = [AstTypeInference]::InferTypeOf($memberAst)
+
+        $res | Should -HaveCount 2
+        $res[0].Name | Should -Be System.ArgumentException
+        $res[1].Name | Should -Be System.NotImplementedException
+    }
+
+    It 'Infers type of $_.Exception in each successive catch block' {
+        $memberAst = {
+            try {}
+            catch [System.ArgumentException] { $_.Exception }
+            catch { $_.Exception }
+        }.Ast.FindAll(
+            { param($a) $a -is [System.Management.Automation.Language.MemberExpressionAst] },
+            $true
+        )
+        $res = foreach ($item in $memberAst) { [AstTypeInference]::InferTypeOf($item) }
+
+        $res | Should -HaveCount 2
+        $res[0].Name | Should -Be System.ArgumentException
+        $res[1].Name | Should -Be System.Exception
+    }
+
     It 'Infers type of function member' {
         $res = [AstTypeInference]::InferTypeOf( {
                 class X {