[XSG] Use absolute file paths when generating #line

Author: simonrozsival

src/Controls/src/SourceGen/PrePost.cs

@@ -15,15 +15,16 @@ class PrePost : IDisposable
 	/// <param name="iXmlLineInfo"></param>
 	/// <param name="fileName"></param>
 	/// <returns></returns>
-	public static PrePost NewLineInfo(IndentedTextWriter codeWriter, IXmlLineInfo iXmlLineInfo, string? fileName)
+	public static PrePost NewLineInfo(IndentedTextWriter codeWriter, IXmlLineInfo iXmlLineInfo, ProjectItem? projectItem)
 	{
-		static void LineInfo(IndentedTextWriter codeWriter, IXmlLineInfo iXmlLineInfo, string? fileName)
-			=> codeWriter.WriteLineNoTabs($"#line {(iXmlLineInfo.LineNumber != -1 ? iXmlLineInfo.LineNumber : 1)} \"{fileName}\"");
+		// Emit #line with an absolute path since relative paths have undefined behavior (https://github.com/dotnet/roslyn/issues/71202#issuecomment-1874649780)
+		static void LineInfo(IndentedTextWriter codeWriter, IXmlLineInfo iXmlLineInfo, ProjectItem? projectItem)
+			=> codeWriter.WriteLineNoTabs($"#line {(iXmlLineInfo.LineNumber != -1 ? iXmlLineInfo.LineNumber : 1)} \"{projectItem?.AbsolutePath}\"");
 
 		static void LineDefault(IndentedTextWriter codeWriter, IXmlLineInfo iXmlLineInfo)
 			=> codeWriter.WriteLineNoTabs("#line default");
 
-		return new(() => LineInfo(codeWriter, iXmlLineInfo, fileName), () => LineDefault(codeWriter, iXmlLineInfo));
+		return new(() => LineInfo(codeWriter, iXmlLineInfo, projectItem), () => LineDefault(codeWriter, iXmlLineInfo));
 	}
 
 	public static PrePost NoBlock() =>

src/Controls/src/SourceGen/ProjectItem.cs

@@ -7,6 +7,8 @@
 namespace Microsoft.Maui.Controls.SourceGen;
 record ProjectItem(AdditionalText AdditionalText, AnalyzerConfigOptions Options)
 {
+	private readonly AdditionalText _additionalText = AdditionalText;
+	
 	public string Configuration
 		=> Options.GetValueOrDefault("build_property.Configuration", "Debug");
 
@@ -62,9 +64,12 @@ public string NoWarn
 	public string? RelativePath
 		=> Options.GetValueOrNull("build_metadata.additionalfiles.RelativePath");
 
+	public string? AbsolutePath
+		=> _additionalText.Path;
+
 	public string? TargetFramework
 		=> Options.GetValueOrNull("build_property.targetFramework");
 
 	public string? TargetPath
-		=> Options.GetValueOrDefault("build_metadata.additionalfiles.TargetPath", AdditionalText.Path);
+		=> Options.GetValueOrDefault("build_metadata.additionalfiles.TargetPath", _additionalText.Path);
 }

src/Controls/src/SourceGen/Visitors/SetPropertiesVisitor.cs

@@ -474,14 +474,14 @@ static void Set(IndentedTextWriter writer, LocalVariable parentVar, string local
 
 		if (node is ValueNode valueNode)
 		{
-			using (context.ProjectItem.EnableLineInfo ? PrePost.NewLineInfo(writer, (IXmlLineInfo)node, context.ProjectItem.RelativePath) : PrePost.NoBlock())
+			using (context.ProjectItem.EnableLineInfo ? PrePost.NewLineInfo(writer, (IXmlLineInfo)node, context.ProjectItem) : PrePost.NoBlock())
 			{
 				var valueString = valueNode.ConvertTo(property, context, parentVar);
 				writer.WriteLine($"{parentVar.Name}.{EscapeIdentifier(localName)} = {valueString};");
 			}
 		}
 		else if (node is ElementNode elementNode)
-			using (context.ProjectItem.EnableLineInfo ? PrePost.NewLineInfo(writer, (IXmlLineInfo)node, context.ProjectItem.RelativePath) : PrePost.NoBlock())
+			using (context.ProjectItem.EnableLineInfo ? PrePost.NewLineInfo(writer, (IXmlLineInfo)node, context.ProjectItem) : PrePost.NoBlock())
 				writer.WriteLine($"{parentVar.Name}.{EscapeIdentifier(localName)} = ({property.Type.ToFQDisplayString()}){(HasDoubleImplicitConversion(context.Variables[elementNode].Type, property.Type, context, out var conv) ? "(" + conv!.ReturnType.ToFQDisplayString() + ")" : string.Empty)}{context.Variables[elementNode].Name};");
 	}
 
@@ -610,7 +610,7 @@ static void Add(IndentedTextWriter writer, LocalVariable parentVar, XmlName prop
 		if (HasDoubleImplicitConversion(context.Variables[valueNode].Type, itemType, context, out var conv))
 			cast = "(" + conv!.ReturnType.ToFQDisplayString() + ")";
 
-		using (context.ProjectItem.EnableLineInfo ? PrePost.NewLineInfo(writer, (IXmlLineInfo)valueNode, context.ProjectItem.RelativePath) : PrePost.NoBlock())
+		using (context.ProjectItem.EnableLineInfo ? PrePost.NewLineInfo(writer, (IXmlLineInfo)valueNode, context.ProjectItem) : PrePost.NoBlock())
 			writer.WriteLine($"{parentObj}.Add(({itemType.ToFQDisplayString()}){cast}{context.Variables[valueNode].Name});");
 	}
 

src/Controls/tests/SourceGen.UnitTests/InitializeComponent/LineInfoTests.cs

@@ -0,0 +1,36 @@
+using System;
+using System.IO;
+using System.Linq;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.Controls.SourceGen.UnitTests.InitializeComponent;
+
+public class LineInfoTests : SourceGenXamlInitializeComponentTestBase
+{
+    [Test]
+    public void DiagnosticShowsLocationInInputXamlFile()
+    {
+        var xaml =
+"""
+<?xml version="1.0" encoding="UTF-8"?>
+<ContentPage
+    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+    x:Class="Test.TestPage">
+    <ContentPage.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceDictionary Source="Resources/Styles\Colors.xaml" />
+            </ResourceDictionary.MergedDictionaries>
+        </ResourceDictionary>
+    </ContentPage.Resources>
+</ContentPage>
+""";
+
+        var (result, _) = RunGenerator(xaml, string.Empty);
+
+        var generatedCode = result.GeneratedTrees.Single(tree => tree.FilePath.EndsWith("_Test.xaml.xsg.cs")).ToString();
+        var expectedFilePath = Path.Combine(Environment.CurrentDirectory, "Test.xaml");
+        Assert.IsTrue(generatedCode.Contains(@$"#line 9 ""{expectedFilePath}""", StringComparison.Ordinal));
+    }
+}

src/Controls/tests/SourceGen.UnitTests/InitializeComponent/SourceGenXamlInitializeComponentTests.cs

@@ -1,3 +1,5 @@
+using System;
+using System.IO;
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -16,7 +18,9 @@ protected record AdditionalXamlFile(string Path, string Content, string? Relativ
 	{
 		var compilation = CreateMauiCompilation();
 		compilation = compilation.AddSyntaxTrees(CSharpSyntaxTree.ParseText(code));
-		var result = RunGenerator<CodeBehindGenerator>(compilation, new AdditionalXamlFile("Test.xaml", xaml, TargetFramework: targetFramework, NoWarn: noWarn));
+		var workingDirectory = Environment.CurrentDirectory;
+		var xamlFile = new AdditionalXamlFile(Path.Combine(workingDirectory, "Test.xaml"), xaml, RelativePath: "Test.xaml", TargetFramework: targetFramework, NoWarn: noWarn);
+		var result = RunGenerator<CodeBehindGenerator>(compilation, xamlFile);
 		var generated = result.Results.SingleOrDefault().GeneratedSources.SingleOrDefault(gs => gs.HintName.EndsWith(".xsg.cs")).SourceText?.ToString();
 
 		return (result, generated);