XPath expression for parsing WiX Processing-Instructions as MsBuild properties - xpath

Question

I have the following wix include VersionFile.wxi
<?xml version="1.0" encoding="utf-8"?>
<Include>
<?define ProductVersionMajor = "1" ?>
<?define ProductVersionMinor = "00" ?>
<?define ProductName= "MyProduct" ?>
<?define UpgradeCode = "myUpgradeCode" ?>
</Include>
Now I want to get e.g. the ProductVersionMajor as "1" or ProductName "MyProduct" (without quotes) using XmlPeek and a XPath query. With following code
<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<Target Name="Test">
<XmlPeek XmlInputPath="VersionFile.wxi"
Query="//processing-instruction('define')[starts-with(., "ProductVersionMajor =")]">
<Output TaskParameter="Result" ItemName="Peeked" />
</XmlPeek>
<XmlPeek XmlInputPath="VersionFile.wxi"
Query="//processing-instruction('define')[starts-with(., "ProductVersionMajor=")]">
<Output TaskParameter="Result" ItemName="Peeked" />
</XmlPeek>
<Message Text="#(Peeked)"/>
</Target>
</Project>
I already got it down to
<?define ProductVersionMajor = "1" ?>
But goal would be
1
Any help how to tweak the XPath query highly appreciated. Also it'll be great to have a placeholder "ProductVersionMajor*=" instead using XmlPeek twice.
<XmlPeek XmlInputPath="ProductVersion.wxi"
Query="substring-before(substring-after(//processing-instruction("define")[starts-with(., "ProductVersionMajor=")],"),")">
<Output TaskParameter="Result" ItemName="Peeked" />
</XmlPeek>
unfortunately only produces an
error MSB3734: XPath Query "substring-before(substring-after(//processing-instruction("define")[starts-with(., "ProductVersionMajor=")],"),")" cannot be loaded. 'substring-before(substring-after(//processing-instruction("define")[starts-with(., "ProductVersionMajor=")],"),")' has an invalid token.
Assume that XmlPeek needs some more custom XPath syntax possibly?
Yes. Tried it as well. Now also tried
Query="substring-before(substring-after(//processing-instruction('define')[starts-with(., 'ProductVersionMajor =')],&apos;"&apos;),&apos;"&apos;) ">
Also no success. Error is
error MSB4018: The "XmlPeek" task failed unexpectedly.\r
error MSB4018: System.Xml.XPath.XPathException: Expression must evaluate to a node-set.\r
error MSB4018: at System.Xml.XPath.XPathNavigator.Select(XPathExpression expr)\r
error MSB4018: at Microsoft.Build.Tasks.XmlPeek.Execute()\r
error MSB4018: at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()\r
error MSB4018: at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, Task
LoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask, Boolean& taskResult)

Answer 1

Form the xpath point of view the following should do:
Query='substring-before(
substring-after(
//processing-instruction("define")[starts-with(., "ProductVersionMajor =")]
,
'"'
)
,
'"'
)'

Answer 2

I solved this problem with this approach. Hope it helps:
<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
<UsingTask TaskName="GetWixDefine"
TaskFactory="CodeTaskFactory"
AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v4.0.dll">
<ParameterGroup>
<File ParameterType="System.String" Required="true" Output="false" />
<DefineName ParameterType="System.String" Required="true" Output="false" />
<Value ParameterType="System.String" Output="true" />
</ParameterGroup>
<Task>
<Reference Include="System.Xml" />
<Using Namespace="System" />
<Using Namespace="System.Text.RegularExpressions" />
<Using Namespace="System.Xml" />
<Code Type="Fragment" Language="cs">
<![CDATA[
this.Value = string.Empty;
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(this.File);
string selector = string.Format("//processing-instruction('define')[starts-with(., '{0}')]", this.DefineName);
XmlNode defineNode = xmlDoc.SelectSingleNode(selector);
if (defineNode == null)
throw new Exception("define not found");
string regex = string.Format("{0}[ ]*=[ ]*\"(?<value>.*)\"", DefineName);
Match match = Regex.Match(defineNode.InnerText, regex);
if (!match.Success)
throw new Exception("cannot match correctly");
this.Value = match.Groups["value"].Value;
]]>
</Code>
</Task>
</UsingTask>
<Target Name="BeforeBuild">
<GetWixDefine File="VersionFile.wxi" DefineName="ProductVersion">
<Output TaskParameter="Value" ItemName="ProductVersionValue"/>
</GetWixDefine>
<Message Importance="High" Text="ProductVersion: #(ProductVersionValue)"/>
</Target>
</Project>