Fix ranges containing only removals

Author: paleite

src/__fixtures__/diff.ts

@@ -34,3 +34,14 @@ index 4d2637c..99dc494 100644
 @@ -10,0 +7,2 @@ if (!myFunc(true == myVar))
 +if (!myFunc(true == myVar)) (myRes = false), (someotherThing = null);
 +unrelated = true;`;
+
+export const includingOnlyRemovals = `diff --git a/dirty.js b/dirty.js
+index cb3c131..874b8f9 100644
+--- a/dirty.js
++++ b/dirty.js
+@@ -1,0 +2,2 @@ if (new Date().getTime()) console.log("curly");
++if (new Date().getTime()) console.log("curly");
++if (new Date().getTime()) console.log("curly");
+@@ -17,2 +16,0 @@ import { a } from "../components/a";
+-import { b } from "../context/b";
+-import { c } from "../context/c";`;

src/__snapshots__/git.test.ts.snap

@@ -16,3 +16,12 @@ Array [
   },
 ]
 `;
+
+exports[`git should work for hunks which include only-removal-ranges 1`] = `
+Array [
+  Range {
+    "exclusiveUpperBound": 4,
+    "inclusiveLowerBound": 2,
+  },
+]
+`;

src/git.test.ts

@@ -1,7 +1,7 @@
 import * as child_process from "child_process";
 import { mocked } from "ts-jest/utils";
 import { getDiffForFile, getRangesForDiff } from "./git";
-import { hunks } from "./__fixtures__/diff";
+import { hunks, includingOnlyRemovals } from "./__fixtures__/diff";
 
 jest.mock("child_process");
 
@@ -12,6 +12,10 @@ describe("git", () => {
     expect(getRangesForDiff(hunks)).toMatchSnapshot();
   });
 
+  it("should work for hunks which include only-removal-ranges", () => {
+    expect(getRangesForDiff(includingOnlyRemovals)).toMatchSnapshot();
+  });
+
   it("should get the staged diff of a file", () => {
     mockedChildProcess.execSync.mockReturnValue(Buffer.from(hunks));
 

src/git.ts

@@ -36,14 +36,22 @@ const getRangeForChangedLines = (line: string) => {
     range.groups?.linesCountDelimiter && range.groups?.linesCount
       ? parseInt(range.groups.linesCount)
       : 1;
+
+  const hasAddedLines = linesCount !== 0;
   const start: number = parseInt(range.groups?.start);
   const end = start + linesCount;
 
-  return new Range(start, end);
+  return hasAddedLines ? new Range(start, end) : null;
 };
 
+const removeNullRanges = (r: Range | null): r is Range => r !== null;
+
 const getRangesForDiff = (diff: string): Range[] => {
-  return diff.split("\n").filter(isHunkHeader).map(getRangeForChangedLines);
+  return diff
+    .split("\n")
+    .filter(isHunkHeader)
+    .map(getRangeForChangedLines)
+    .filter(removeNullRanges);
 };
 
 export { getDiffForFile, getRangesForDiff };