From f01338fa338c3efdd628cc45970593a091de1b9f Mon Sep 17 00:00:00 2001
From: Ryan Cavanaugh <RyanCavanaugh@users.noreply.github.com>
Date: Mon, 14 May 2018 18:27:21 -0700
Subject: [PATCH] Comments/naming

---
 src/server/session.ts    |  7 +++++++
 src/services/services.ts | 12 ++++++------
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/server/session.ts b/src/server/session.ts
index 6cd3a7df560..d0c58b20922 100644
--- a/src/server/session.ts
+++ b/src/server/session.ts
@@ -700,6 +700,13 @@ namespace ts.server {
             return definitions.map(def => this.toFileSpan(def.fileName, def.textSpan, project));
         }
 
+        /*
+         * When we map a .d.ts location to .ts, Visual Studio gets confused because there's no associated Roslyn Document in
+         * the same project which corresponds to the file. VS Code has no problem with this, and luckily we have two protocols.
+         * This retains the existing behavior for the "simplified" (VS Code) protocol but stores the .d.ts location in a
+         * set of additional fields, and does the reverse for VS (store the .d.ts location where
+         * it used to be and stores the .ts location in the additional fields).
+        */
         private static mapToOriginalLocation<T extends DocumentSpan>(def: T): T {
             if (def.originalFileName) {
                 Debug.assert(def.originalTextSpan !== undefined, "originalTextSpan should be present if originalFileName is");
diff --git a/src/services/services.ts b/src/services/services.ts
index 628892960af..3fcd4e8e151 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1600,10 +1600,10 @@ namespace ts {
 
         function makeGetTargetOfMappedPosition<TIn>(
             extract: (original: TIn) => sourcemaps.SourceMappableLocation,
-            create: (result: sourcemaps.SourceMappableLocation, original: TIn, firstOriginal: TIn) => TIn
+            create: (result: sourcemaps.SourceMappableLocation, unmapped: TIn, original: TIn) => TIn
         ) {
             return getTargetOfMappedPosition;
-            function getTargetOfMappedPosition(input: TIn, firstOriginal = input): TIn {
+            function getTargetOfMappedPosition(input: TIn, original = input): TIn {
                 const info = extract(input);
                 if (endsWith(info.fileName, Extension.Dts)) {
                     let file: SourceFileLike = program.getSourceFile(info.fileName);
@@ -1617,7 +1617,7 @@ namespace ts {
                     const mapper = getSourceMapper(info.fileName, file);
                     const newLoc = mapper.getOriginalPosition(info);
                     if (newLoc === info) return input;
-                    return getTargetOfMappedPosition(create(newLoc, input, firstOriginal), firstOriginal);
+                    return getTargetOfMappedPosition(create(newLoc, input, original), original);
                 }
                 return input;
             }
@@ -1625,7 +1625,7 @@ namespace ts {
 
         const getTargetOfMappedDeclarationInfo = makeGetTargetOfMappedPosition(
             (info: DefinitionInfo) => ({ fileName: info.fileName, position: info.textSpan.start }),
-            (newLoc, info, firstOriginal) => ({
+            (newLoc, info, original) => ({
                 containerKind: info.containerKind,
                 containerName: info.containerName,
                 fileName: newLoc.fileName,
@@ -1635,8 +1635,8 @@ namespace ts {
                     start: newLoc.position,
                     length: info.textSpan.length
                 },
-                originalFileName: firstOriginal.fileName,
-                originalTextSpan: firstOriginal.textSpan
+                originalFileName: original.fileName,
+                originalTextSpan: original.textSpan
             })
         );