Add missing container-parameters to Data before BeforeDiscovery

src/Main.ps1

@@ -1712,6 +1712,11 @@ function BeforeDiscovery {
     )
 
     if ($ExecutionContext.SessionState.PSVariable.Get('invokedViaInvokePester')) {
+        if ($state.CurrentBlock.IsRoot -and -not $state.CurrentBlock.FrameworkData.MissingParametersProcessed) {
+            # For undefined parameters in container, add parameter's default value to Data
+            Add-MissingContainerParameters -RootBlock $state.CurrentBlock -Container $container -CallingFunction $PSCmdlet
+        }
+
         . $ScriptBlock
     }
     else {

src/Pester.Runtime.ps1

@@ -2702,4 +2702,6 @@ function Add-MissingContainerParameters ($RootBlock, $Container, $CallingFunctio
             }
         }
     }
+
+    $RootBlock.FrameworkData.MissingParametersProcessed = $true
 }

src/functions/Context.ps1

@@ -96,7 +96,7 @@
     }
 
     if ($ExecutionContext.SessionState.PSVariable.Get('invokedViaInvokePester')) {
-        if ($state.CurrentBlock.IsRoot -and $state.CurrentBlock.Blocks.Count -eq 0) {
+        if ($state.CurrentBlock.IsRoot -and -not $state.CurrentBlock.FrameworkData.MissingParametersProcessed) {
             # For undefined parameters in container, add parameter's default value to Data
             Add-MissingContainerParameters -RootBlock $state.CurrentBlock -Container $container -CallingFunction $PSCmdlet
         }

src/functions/Describe.ps1

@@ -104,7 +104,7 @@
     }
 
     if ($ExecutionContext.SessionState.PSVariable.Get('invokedViaInvokePester')) {
-        if ($state.CurrentBlock.IsRoot -and $state.CurrentBlock.Blocks.Count -eq 0) {
+        if ($state.CurrentBlock.IsRoot -and -not $state.CurrentBlock.FrameworkData.MissingParametersProcessed) {
             # For undefined parameters in container, add parameter's default value to Data
             Add-MissingContainerParameters -RootBlock $state.CurrentBlock -Container $container -CallingFunction $PSCmdlet
         }

tst/Pester.RSpec.ts.ps1

@@ -1540,6 +1540,48 @@ i -PassThru:$PassThru {
                 }
             }
         }
+
+        t "Parameter default values aren't overriden by changes in BeforeDiscovery" {
+            # https://github.com/pester/Pester/issues/2359
+            $sb = {
+                param (
+                    [int] $Value = 123
+                )
+
+                if ($Value -ne 123) {
+                    throw "Expected `$Value to be 123, but it is, '$Value'"
+                }
+
+                # KNOWN ISSUE: Changes to $Value here, outside BeforeDiscovery, would be used as parameter default value in Data.
+                # Can't fix as we don't have a hook beetween script execution and first call to a Pester-function
+
+                BeforeDiscovery {
+                    $Value = 456 # Should not override default value in Data
+                }
+
+                BeforeAll {
+                    if ($Value -ne 123) {
+                        throw "Expected `$Value to be 123 but it is, '$Value'"
+                    }
+                }
+
+                Describe 'd1' {
+                    It 't1' {
+                        if ($Value -ne 123) {
+                            throw "Expected `$Value to be 123 but it is, '$Value'"
+                        }
+                    }
+                }
+            }
+
+            $container = New-PesterContainer -ScriptBlock $sb -Data @{ }
+            $r = Invoke-Pester -Container $container -PassThru
+
+            $r.Containers[0].Data.ContainsKey('Value') | Verify-True
+            $r.Containers[0].Data['Value'] | Verify-Equal 123
+
+            $r.Containers[0].Blocks[0].Tests[0].Result | Verify-Equal 'Passed'
+        }
     }
 
     b "New-PesterContainer" {