Add line mappings to project TagHelper attribute values.

- We now create LineMappings for instances where a TagHelper's attribute value is not of a string type.
- This will enable the Razor editor to create projections from .cshtml => .cs for TagHelper attributes.
- Modified the TagHelperCodeGenerator and TagHelperBlockBuiler to accurately track the attribute values start locations so it could flow into code generation.
- Modified existing tests to account for the new line mappings.

#207

Author: N. Taylor Mullen

src/Microsoft.AspNet.Razor/Generator/Compiler/CodeBuilder/CSharp/CSharpTagHelperCodeRenderer.cs

@@ -6,6 +6,7 @@
 using System.Globalization;
 using System.Linq;
 using Microsoft.AspNet.Razor.TagHelpers;
+using Microsoft.AspNet.Razor.Text;
 
 namespace Microsoft.AspNet.Razor.Generator.Compiler.CSharp
 {
@@ -249,7 +250,7 @@ private void RenderBoundHTMLAttributes(IDictionary<string, Chunk> chunkAttribute
 
                             // We aren't a bufferable attribute which means we have no Razor code in our value.
                             // Therefore we can just use the "textValue" as the attribute value.
-                            RenderRawAttributeValue(textValue, attributeDescriptor);
+                            RenderRawAttributeValue(textValue, attributeValueChunk.Start, attributeDescriptor);
                         }
 
                         // End the assignment to the attribute.
@@ -405,13 +406,26 @@ private void RenderBufferedAttributeValue(TagHelperAttributeDescriptor attribute
                 });
         }
 
-        private void RenderRawAttributeValue(string value, TagHelperAttributeDescriptor attributeDescriptor)
+        private void RenderRawAttributeValue(string value,
+                                             SourceLocation documentLocation,
+                                             TagHelperAttributeDescriptor attributeDescriptor)
         {
             RenderAttributeValue(
                 attributeDescriptor,
                 valueRenderer: (writer) =>
                 {
-                    writer.Write(value);
+                    // We only want to do the work of generating a line mapping if we're in design time mode.
+                    if (_context.Host.DesignTimeMode)
+                    {
+                        using (new CSharpLineMappingWriter(_writer, documentLocation, value.Length))
+                        {
+                            writer.Write(value);
+                        }
+                    }
+                    else
+                    {
+                        writer.Write(value);
+                    }
                 });
         }
 

src/Microsoft.AspNet.Razor/Generator/TagHelperCodeGenerator.cs

@@ -3,10 +3,12 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.AspNet.Razor.Generator.Compiler;
 using Microsoft.AspNet.Razor.Parser.SyntaxTree;
 using Microsoft.AspNet.Razor.Parser.TagHelpers;
 using Microsoft.AspNet.Razor.TagHelpers;
+using Microsoft.AspNet.Razor.Text;
 
 namespace Microsoft.AspNet.Razor.Generator
 {
@@ -63,7 +65,8 @@ public override void GenerateStartBlockCode(Block target, CodeGeneratorContext c
 
                 attributes[attribute.Key] = new ChunkBlock
                 {
-                    Children = chunks
+                    Children = chunks,
+                    Start = chunks.FirstOrDefault()?.Start ?? SourceLocation.Zero
                 };
 
                 // Reset the code tree builder so we can build a new one for the next attribute

src/Microsoft.AspNet.Razor/Parser/TagHelpers/TagHelperBlockBuilder.cs

@@ -159,6 +159,8 @@ private static KeyValuePair<string, SyntaxTreeNode> ParseSpan(
                 Kind = span.Kind
             };
             var htmlSymbols = span.Symbols.OfType<HtmlSymbol>().ToArray();
+            var capturedAttributeValueStart = false;
+            var attributeValueStartLocation = span.Start;
             var symbolOffset = 1;
             string name = null;
 
@@ -174,6 +176,16 @@ private static KeyValuePair<string, SyntaxTreeNode> ParseSpan(
                 }
                 else if (afterEquals)
                 {
+                    // When symbols are accepted into SpanBuilders their locations get altered to abide by the 
+                    // parent which is why we need to mark our start location prior to adding the symbol so we know
+                    // the location of the attribute value start within the document.
+                    if (!capturedAttributeValueStart)
+                    {
+                        capturedAttributeValueStart = true;
+
+                        attributeValueStartLocation += symbol.Start;
+                    }
+
                     builder.Accept(symbol);
                 }
                 else if (symbol.Type == HtmlSymbolType.Equals)
@@ -202,6 +214,10 @@ private static KeyValuePair<string, SyntaxTreeNode> ParseSpan(
                 }
             }
 
+            // After all symbols have been added we need to offset the builders start position. Adding symbols to a
+            // SpanBuilder alters its position prior to it being occupied.
+            builder.Start = attributeValueStartLocation;
+
             return CreateMarkupAttribute(name, builder, attributeValueTypes);
         }
 

test/Microsoft.AspNet.Razor.Test/Generator/CSharpTagHelperRenderingTest.cs

@@ -81,7 +81,14 @@ public static TheoryData DesignTimeTagHelperTestData
                                              generatedAbsoluteIndex: 475,
                                              generatedLineIndex: 15,
                                              characterOffsetIndex: 14,
-                                             contentLength: 11)
+                                             contentLength: 11),
+                            BuildLineMapping(documentAbsoluteIndex: 57,
+                                             documentLineIndex: 2,
+                                             documentCharacterOffsetIndex: 28,
+                                             generatedAbsoluteIndex: 927,
+                                             generatedLineIndex: 33,
+                                             generatedCharacterOffsetIndex: 31,
+                                             contentLength: 4)
                         }
                     },
                     {
@@ -95,7 +102,14 @@ public static TheoryData DesignTimeTagHelperTestData
                                              generatedAbsoluteIndex: 475,
                                              generatedLineIndex: 15,
                                              characterOffsetIndex: 14,
-                                             contentLength: 11)
+                                             contentLength: 11),
+                            BuildLineMapping(documentAbsoluteIndex: 189,
+                                             documentLineIndex: 6,
+                                             documentCharacterOffsetIndex: 40,
+                                             generatedAbsoluteIndex: 1599,
+                                             generatedLineIndex: 44,
+                                             generatedCharacterOffsetIndex: 40,
+                                             contentLength: 4)
                         }
                     },
                     {
@@ -125,6 +139,7 @@ public static TheoryData DesignTimeTagHelperTestData
                             BuildLineMapping(218, 9, 13, 1356, 56, 12, 27),
                             BuildLineMapping(346, 12, 1754, 68, 0, 48),
                             BuildLineMapping(440, 15, 46, 2004, 78, 6, 8),
+                            BuildLineMapping(457, 15, 63, 2267, 85, 40, 4),
                             BuildLineMapping(501, 16, 31, 2384, 88, 6, 30),
                             BuildLineMapping(568, 17, 30, 2733, 97, 0, 10),
                             BuildLineMapping(601, 17, 63, 2815, 103, 0, 8),