git blame --reverse doesn't find line in HEAD

From: Nick Snyder <nick@sourcegraph.com>
Date: Nov 29, 2017, 08:06 UTC
Message-ID: <CA+SQVf1W6BhNyB6bGxh7WfCwb6+E3pNjHLeS4xDYPJ6BLT8cng@mail.gmail.com>

I have a repo that reproduces a behavior with `git blame --reverse` that surprises me. https://github.com/nicksnyder/git-blame-bug

The readme explains the observed behavior and what I expected to happen. I will inline the readme at the bottom of this message for convenience.

Am I misunderstanding --reverse or is this a bug?

Thanks! Nick

$ git --version git version 2.15.0

Blame of L465 in Tree.tsx at HEAD (ca0fb5) points to L463 at 199ee7

$ git blame -p -L465,465 Tree.tsx
199ee75d1240ae72cd965f62aceeb301ab64e1bd 463 465 1
filename Tree.tsx
            public shouldComponentUpdate(nextProps: TileProps): boolean {

EXPECTED: Reverse blame of L463 at 199ee7 points to L465 at the
lastest commit in the repo (at least ca0fb5).
ACTUAL: Reverse blame of L463 at 199ee7 points to L463 at 199ee7.

$ git blame -p -L463,463 --reverse 199ee7.. Tree.tsx
199ee75d1240ae72cd965f62aceeb301ab64e1bd 463 463 1
boundary
previous ca0fb5a2d61cb16909bcb06f49dd5448a26f32b1 Tree.tsx
filename Tree.tsx
            public shouldComponentUpdate(nextProps: TileProps): boolean {

The line in question is in the diff (git diff 199ee7..ca0fb5), but that particular line is neither added nor deleted, so I don't know why blame would think it is deleted.

Relevant hunk in diff:

@@ -452,28 +462,17 @@ export class LayerTile extends
React.Component<TileProps, {}> {
         }
     }

-    public validTokenRange(props: TileProps): boolean {
-        if (props.selectedPath === '') {
-            return true
-        }
-        const token = props.selectedPath.split('/').pop()!
-        return token >= this.first && token <= this.last
-    }
-
     public shouldComponentUpdate(nextProps: TileProps): boolean {
-        const lastValid = this.validTokenRange(this.props)
-        const nextValid = this.validTokenRange(nextProps)
-        if (!lastValid && !nextValid) {
-            // short circuit
-            return false
+        if (isEqualOrAncestor(this.props.selectedDir,
this.props.currSubpath)) {
+            return true
         }
-        if (isEqualOrAncestor(this.props.selectedDir,
this.props.currSubpath) && lastValid) {
+        if (nextProps.selectedDir === nextProps.currSubpath) {
             return true
         }
-        if (nextProps.selectedDir === nextProps.currSubpath &&
this.validTokenRange(nextProps)) {
+        if (getParentDir(nextProps.selectedDir) === nextProps.currSubpath) {
             return true
         }
-        if (getParentDir(nextProps.selectedDir) ===
nextProps.currSubpath && this.validTokenRange(nextProps)) {
+        if (!isEqual(nextProps.pathSplits, this.props.pathSplits)) {
             return true
         }
         return false