git branch - Spurious change when using git diff <base>...<feature> -

github seems use triple dot comparison on pull requests, tricked me today showing spurious change between feature , base branch.

here base branch (abbreviated):

git show upstream/develop:script.sql  field in (          [001*a], [001*d], [001*y], [001*x], [001*z],          [004*a],          [008*a], [008*d], [008*j], [008*l], [008*o],          [009*a], [009*b], [009*g], [009*x], [009*u],          [041*a], [041*c], 

here feature branch (abbreviated):

git show feature:script.sql  field in (          [001*a], [001*d], [001*y], [001*x], [001*z],          [004*a],          [008*a], [008*d], [008*j], [008*l], [008*o],          [009*a], [009*b], [009*g], [009*x], [009*u],          [041*a], [041*c], 

here output plain diff:

git diff upstream/develop feature script.sql 

(no output.)

here output "changed on feature branch"-triple dot operator diff:

git diff upstream/develop...feature script.sql   field in (           [001*a], [001*d], [001*y], [001*x], [001*z], +         [004*a],           [008*a], [008*d], [008*j], [008*l], [008*o], 

why?

there no change on line. adding -w shouldn't necessary since plain diff above run without , reported no change.

from git diff

git diff [--options] [--] [...]

this view changes between 2 arbitrary < commit >.

...

git diff [--options] ... [--] [...]

this form view changes on branch containing , second , starting @ common ancestor of both . "git diff a...b" equivalent "git diff $(git-merge-base b) b". can omit 1 of , has same effect using head instead.

...

however, "diff" comparing 2 endpoints, not ranges, , range notations (".." , "...") not mean range defined in "specifying ranges" section in git-rev-parse(1)

assuming have 2 branches

a-b-c-d (branch1)    \     e-f (branch2)  

git diff branch1 branch2 myfile give diff between file content in d , f.

git diff branch1...branch2 give diff between file content in b , f.

in case [004*a], may have been included in both branches, after b.