git merge-tree

gistfile1.sh

MacBook-Pro:review tibor$ gl
* 3a48299 (origin/alice, alice) alice fix
| * 8dc2ba1 (origin/bob, bob) bob fix
|/
* af5062b (HEAD, origin/master, master) first commit

MacBook-Pro:review tibor$ ls
test.js

MacBook-Pro:review tibor$ cat test.js
// flat fees and taxes
var customsFee          = 5.5;
var immigrationFee      = 7;
var federalTransportTax = .025;

function calculateAirfare(baseFare) {
	var fare = baseFare;
	fare += immigrationFee;
	fare *= (1 + federalTransportTax);
	return fare;
}

MacBook-Pro:review tibor$ # customsFee is not used, so both bob and alice will fix it without knowing the other is fixing it

MacBook-Pro:review tibor$ git diff master..alice
diff --git a/test.js b/test.js
index cbc9ef2..d3358c8 100644
--- a/test.js
+++ b/test.js
@@ -5,6 +5,7 @@ var federalTransportTax = .025;

 function calculateAirfare(baseFare) {
        var fare = baseFare;
+       fare += customsFee;
        fare += immigrationFee;
        fare *= (1 + federalTransportTax);
        return fare;

MacBook-Pro:review tibor$ git diff master..bob
diff --git a/test.js b/test.js
index cbc9ef2..d6cbcac 100644
--- a/test.js
+++ b/test.js
@@ -6,6 +6,7 @@ var federalTransportTax = .025;
 function calculateAirfare(baseFare) {
        var fare = baseFare;
        fare += immigrationFee;
+       fare += customsFee;
        fare *= (1 + federalTransportTax);
        return fare;
 }

MacBook-Pro:review tibor$ # they both fixed it, but not on the same line
MacBook-Pro:review tibor$ # let's say alice's fix got merged first

MacBook-Pro:review tibor$ git merge alice
Updating af5062b..3a48299
Fast-forward
 test.js | 1 +
 1 file changed, 1 insertion(+)

MacBook-Pro:review tibor$ gl
* 3a48299 (HEAD, origin/alice, master, alice) alice fix
| * 8dc2ba1 (origin/bob, bob) bob fix
|/
* af5062b (origin/master) first commit

MacBook-Pro:review tibor$ git diff master..bob
diff --git a/test.js b/test.js
index d3358c8..d6cbcac 100644
--- a/test.js
+++ b/test.js
@@ -5,8 +5,8 @@ var federalTransportTax = .025;

 function calculateAirfare(baseFare) {
        var fare = baseFare;
-       fare += customsFee;
        fare += immigrationFee;
+       fare += customsFee;
        fare *= (1 + federalTransportTax);
        return fare;
 }

MacBook-Pro:review tibor$ # this is incorrect, it's not what's going to happen if we merge bob's fix

MacBook-Pro:review tibor$ git diff master...bob
diff --git a/test.js b/test.js
index cbc9ef2..d6cbcac 100644
--- a/test.js
+++ b/test.js
@@ -6,6 +6,7 @@ var federalTransportTax = .025;
 function calculateAirfare(baseFare) {
        var fare = baseFare;
        fare += immigrationFee;
+       fare += customsFee;
        fare *= (1 + federalTransportTax);
        return fare;
 }

MacBook-Pro:review tibor$ # triple dot is even more so incorrect, since we don't see alice's fix
MacBook-Pro:review tibor$ # the only way to see this is to merge in memory and do diff, that's what merge-tree does apparently

MacBook-Pro:review tibor$ git merge-tree $(git merge-base master bob) master bob
changed in both
  base   100644 cbc9ef2e2fb0c86c79a7494494072e0c720e8d79 test.js
  our    100644 d3358c8350fa76ad69cbe52fabd82b3378c92bac test.js
  their  100644 d6cbcac7c826c79ea7629e3077f9266fa909d80e test.js
@@ -7,6 +7,7 @@
 	var fare = baseFare;
 	fare += customsFee;
 	fare += immigrationFee;
+	fare += customsFee;
 	fare *= (1 + federalTransportTax);
 	return fare;
 }

MacBook-Pro:review tibor$ # there we can see the correct diff, however it is not in the usual git diff format