Shift dynamic positional parameters, fix #217

Invoke-Build.ps1

@@ -118,6 +118,11 @@ if ($_.get_Count()) {
 	foreach($p in $_.get_Values()) {
 		if ($c -notcontains ($_ = $p.Name)) {
 			if ($r -contains $_) {throw "Script uses reserved parameter '$_'."}
+			foreach ($a in $p.Attributes) {
+				if ($a -is [System.Management.Automation.ParameterAttribute] -and $a.Position -ne 0x80000000) {
+					$a.Position += 2
+				}
+			}
 			${*}.DP.Add($_, (New-Object System.Management.Automation.RuntimeDefinedParameter $_, $p.ParameterType, $p.Attributes))
 		}
 	}

Release-Notes.md

@@ -2,6 +2,8 @@
 
 ## v5.10.6
 
+Fix cryptic errors on unknown parameters, #217
+
 Minor tweaks, new demo Tasks/Repeat2, etc.
 
 `Show-BuildGraph.ps1`

Tests/Fixed.test.ps1

@@ -490,52 +490,6 @@ task PreserveCheckpoint {
 	Remove-Item z.build.ps1
 }
 
-# Issue #152 (1). Also test the bootstrapping scenario.
-# This used to fail on the second call of z.ps1.
-task DoNotMakeScriptParametersNamed {
-	# self-invoking build script
-	Set-Content z.ps1 {
-		param(
-			[Parameter()]$Tasks
-		)
-		if (!$MyInvocation.ScriptName.EndsWith('Invoke-Build.ps1')) {
-			return Invoke-Build $Tasks $MyInvocation.MyCommand.Path @PSBoundParameters
-		}
-		task Test {}
-	}
-
-	# invoke the script twice with the task name
-	./z.ps1 Test
-	./z.ps1 Test
-
-	remove z.ps1
-}
-
-<#
-	Issue #152 (2). Test positional parameters.
-	Potential problem:
-		- `Task` and `P1` both have position 0.
-		- `File` and `P2` both have position 1.
-	Fortunate current behaviour:
-		PowerShell somehow does what we expect, shift positions of P1, P2, P3.
-		This may change in the future, so let at least cover this by test.
-	Workarounds for the future:
-		- Use `[CmdletBinding(PositionalBinding=$false)]` (PowerShell v3+) to enforce named parameters.
-		- Set parameter positions explicitly starting with 2 (0, 1 are consumed by Task, File).
-#>
-task PositionalParameters {
-	Set-Content z.build.ps1 {
-		param($P1, $P2, $P3)
-		task Parameters {"$P1|$P2|$P3"}
-	}
-
-	# invoke the script with 5 positional parameters
-	($r = Invoke-Build Parameters z.build.ps1 v1 v2 v3)
-	assert ($r -contains 'v1|v2|v3')
-
-	remove z.build.ps1
-}
-
 # Issue #183, introduce $OriginalLocation, where the build starts.
 task OriginalLocation {
 	Set-Location $HOME

Tests/Issues/152-positional-script-parameters/152.test.ps1

@@ -0,0 +1,48 @@
+
+# Issue #152 (1). Also test the bootstrapping scenario.
+# This used to fail on the second call of z.ps1.
+task DoNotMakeScriptParametersNamed {
+	# self-invoking build script
+	Set-Content z.ps1 {
+		param(
+			[Parameter()]$Tasks
+		)
+		if (!$MyInvocation.ScriptName.EndsWith('Invoke-Build.ps1')) {
+			return Invoke-Build $Tasks $MyInvocation.MyCommand.Path @PSBoundParameters
+		}
+		task Test {}
+	}
+
+	# invoke the script twice with the task name
+	./z.ps1 Test
+	./z.ps1 Test
+
+	remove z.ps1
+}
+
+<#
+	Issue #152 (2). Test positional parameters.
+	Potential problem:
+		- `Task` and `P1` both have position 0.
+		- `File` and `P2` both have position 1.
+		UPDATE: yes, it is a problem, see #217
+	Fortunate current behaviour:
+		PowerShell somehow does what we expect, shift positions of P1, P2, P3.
+		This may change in the future, so let at least cover this by test.
+	Workarounds for the future:
+		- Use `[CmdletBinding(PositionalBinding=$false)]` (PowerShell v3+) to enforce named parameters.
+		- Set parameter positions explicitly starting with 2 (0, 1 are consumed by Task, File).
+		UPDATE: This is used by #217 (shift +2)
+#>
+task PositionalParameters {
+	Set-Content z.build.ps1 {
+		param($P1, $P2, $P3)
+		task Parameters {"$P1|$P2|$P3"}
+	}
+
+	# invoke the script with 5 positional parameters
+	($r = Invoke-Build Parameters z.build.ps1 v1 v2 v3)
+	assert ($r -contains 'v1|v2|v3')
+
+	remove z.build.ps1
+}

Tests/Issues/217-bad-error-on-unknown-parameter/217.build.ps1

@@ -0,0 +1,10 @@
+<# https://github.com/nightroman/Invoke-Build/issues/217
+#152 fixed one issue but added another, cryptic errors.
+#217 shifts script parameters positions (+2) avoiding conflicts with IB Task and File.
+#>
+
+param(
+	$MyParam1 #! this parameter position 0 conflicts with IB Task
+)
+
+task .

Tests/Issues/217-bad-error-on-unknown-parameter/217.test.ps1

@@ -0,0 +1,9 @@
+
+task UnknownParameter {
+	try {
+		throw Invoke-Build -bar
+	}
+	catch {
+		equals "$_" "A parameter cannot be found that matches parameter name 'bar'."
+	}
+}