From 925582d03487b2ca3c2454527c9bedca60ccec6c Mon Sep 17 00:00:00 2001
From: Ben Lichtman <belichtm@microsoft.com>
Date: Tue, 17 Dec 2019 17:04:54 -0800
Subject: [PATCH 1/3] Add asserts to narrow down position issue

---
 src/server/scriptInfo.ts | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/server/scriptInfo.ts b/src/server/scriptInfo.ts
index 15ab756887c..4f471d6ab37 100644
--- a/src/server/scriptInfo.ts
+++ b/src/server/scriptInfo.ts
@@ -622,7 +622,10 @@ namespace ts.server {
         }
 
         positionToLineOffset(position: number): protocol.Location {
-            return this.textStorage.positionToLineOffset(position);
+            const location = this.textStorage.positionToLineOffset(position);
+            Debug.assert(typeof location.line === "number" && location.line > 0, `Expected line ${location.line} to be greater than 0.`);
+            Debug.assert(typeof location.offset === "number" && location.offset > 0, `Expected offset ${location.offset} to be greater than 0.`);
+            return location;
         }
 
         public isJavaScript() {

From 42dc4155ce13d80f31875d2525f64e31e4180927 Mon Sep 17 00:00:00 2001
From: Ben Lichtman <belichtm@microsoft.com>
Date: Tue, 17 Dec 2019 17:41:38 -0800
Subject: [PATCH 2/3] Refactor to make failure messages more consistent

---
 src/server/scriptInfo.ts | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/server/scriptInfo.ts b/src/server/scriptInfo.ts
index 4f471d6ab37..e3f4bd2d195 100644
--- a/src/server/scriptInfo.ts
+++ b/src/server/scriptInfo.ts
@@ -623,8 +623,7 @@ namespace ts.server {
 
         positionToLineOffset(position: number): protocol.Location {
             const location = this.textStorage.positionToLineOffset(position);
-            Debug.assert(typeof location.line === "number" && location.line > 0, `Expected line ${location.line} to be greater than 0.`);
-            Debug.assert(typeof location.offset === "number" && location.offset > 0, `Expected offset ${location.offset} to be greater than 0.`);
+            failIfInvalidLocation(location);
             return location;
         }
 
@@ -645,4 +644,13 @@ namespace ts.server {
             }
         }
     }
+
+    /*@internal*/
+    function failIfInvalidLocation(location: protocol.Location) {
+        Debug.assert(typeof location.line === "number", `Expected line ${location.line} to be a number.`);
+        Debug.assert(typeof location.offset === "number", `Expected offset ${location.offset} to be a number.`);
+
+        Debug.assert(location.line > 0, `Expected line to be non-${location.line === 0 ? "zero" : "negative"}`);
+        Debug.assert(location.offset > 0, `Expected offset to be non-${location.offset === 0 ? "zero" : "negative"}`);
+    }
 }

From 9f1e389441bb5ec92338c216df45efbcd0a008de Mon Sep 17 00:00:00 2001
From: Ben Lichtman <belichtm@microsoft.com>
Date: Wed, 18 Dec 2019 10:44:40 -0800
Subject: [PATCH 3/3] Remove unnecessary internal tags, handle bad input

---
 src/server/scriptInfo.ts | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/server/scriptInfo.ts b/src/server/scriptInfo.ts
index e3f4bd2d195..53bbc6cba75 100644
--- a/src/server/scriptInfo.ts
+++ b/src/server/scriptInfo.ts
@@ -622,6 +622,7 @@ namespace ts.server {
         }
 
         positionToLineOffset(position: number): protocol.Location {
+            failIfInvalidPosition(position);
             const location = this.textStorage.positionToLineOffset(position);
             failIfInvalidLocation(location);
             return location;
@@ -645,7 +646,11 @@ namespace ts.server {
         }
     }
 
-    /*@internal*/
+    function failIfInvalidPosition(position: number) {
+        Debug.assert(typeof position === "number", `Expected position ${position} to be a number.`);
+        Debug.assert(position >= 0, `Expected position to be non-negative.`);
+    }
+
     function failIfInvalidLocation(location: protocol.Location) {
         Debug.assert(typeof location.line === "number", `Expected line ${location.line} to be a number.`);
         Debug.assert(typeof location.offset === "number", `Expected offset ${location.offset} to be a number.`);