git-commit-vandalism/t/t3033-merge-toplevel.sh
Junio C Hamano e379fdf34f merge: refuse to create too cool a merge by default
While it makes sense to allow merging unrelated histories of two
projects that started independently into one, in the way "gitk" was
merged to "git" itself aka "the coolest merge ever", such a merge is
still an unusual event.	 Worse, if somebody creates an independent
history by starting from a tarball of an established project and
sends a pull request to the original project, "git merge" however
happily creates such a merge without any sign of something unusual
is happening.

Teach "git merge" to refuse to create such a merge by default,
unless the user passes a new "--allow-unrelated-histories" option to
tell it that the user is aware that two unrelated projects are
merged.

Because such a "two project merge" is a rare event, a configuration
option to always allow such a merge is not added.

We could add the same option to "git pull" and have it passed
through to underlying "git merge".  I do not have a fundamental
opposition against such a feature, but this commit does not do so
and instead leaves it as low-hanging fruit for others, because such
a "two project merge" would be done after fetching the other project
into some location in the working tree of an existing project and
making sure how well they fit together, it is sufficient to allow a
local merge without such an option pass-through from "git pull" to
"git merge".  Many tests that are updated by this patch does the
pass-through manually by turning:

	git pull something

into its equivalent:

	git fetch something &&
	git merge --allow-unrelated-histories FETCH_HEAD

If somebody is inclined to add such an option, updated tests in this
change need to be adjusted back to:

	git pull --allow-unrelated-histories something

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-03-23 12:04:48 -07:00

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#!/bin/sh
test_description='"git merge" top-level frontend'
. ./test-lib.sh
t3033_reset () {
git checkout -B master two &&
git branch -f left three &&
git branch -f right four
}
test_expect_success setup '
test_commit one &&
git branch left &&
git branch right &&
test_commit two &&
git checkout left &&
test_commit three &&
git checkout right &&
test_commit four &&
git checkout --orphan five &&
test_commit five &&
git checkout master
'
# Local branches
test_expect_success 'merge an octopus into void' '
t3033_reset &&
git checkout --orphan test &&
git rm -fr . &&
test_must_fail git merge left right &&
test_must_fail git rev-parse --verify HEAD &&
git diff --quiet &&
test_must_fail git rev-parse HEAD
'
test_expect_success 'merge an octopus, fast-forward (ff)' '
t3033_reset &&
git reset --hard one &&
git merge left right &&
# one is ancestor of three (left) and four (right)
test_must_fail git rev-parse --verify HEAD^3 &&
git rev-parse HEAD^1 HEAD^2 | sort >actual &&
git rev-parse three four | sort >expect &&
test_cmp expect actual
'
test_expect_success 'merge octopus, non-fast-forward (ff)' '
t3033_reset &&
git reset --hard one &&
git merge --no-ff left right &&
# one is ancestor of three (left) and four (right)
test_must_fail git rev-parse --verify HEAD^4 &&
git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
git rev-parse one three four | sort >expect &&
test_cmp expect actual
'
test_expect_success 'merge octopus, fast-forward (does not ff)' '
t3033_reset &&
git merge left right &&
# two (master) is not an ancestor of three (left) and four (right)
test_must_fail git rev-parse --verify HEAD^4 &&
git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
git rev-parse two three four | sort >expect &&
test_cmp expect actual
'
test_expect_success 'merge octopus, non-fast-forward' '
t3033_reset &&
git merge --no-ff left right &&
test_must_fail git rev-parse --verify HEAD^4 &&
git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
git rev-parse two three four | sort >expect &&
test_cmp expect actual
'
# The same set with FETCH_HEAD
test_expect_success 'merge FETCH_HEAD octopus into void' '
t3033_reset &&
git checkout --orphan test &&
git rm -fr . &&
git fetch . left right &&
test_must_fail git merge FETCH_HEAD &&
test_must_fail git rev-parse --verify HEAD &&
git diff --quiet &&
test_must_fail git rev-parse HEAD
'
test_expect_success 'merge FETCH_HEAD octopus fast-forward (ff)' '
t3033_reset &&
git reset --hard one &&
git fetch . left right &&
git merge FETCH_HEAD &&
# one is ancestor of three (left) and four (right)
test_must_fail git rev-parse --verify HEAD^3 &&
git rev-parse HEAD^1 HEAD^2 | sort >actual &&
git rev-parse three four | sort >expect &&
test_cmp expect actual
'
test_expect_success 'merge FETCH_HEAD octopus non-fast-forward (ff)' '
t3033_reset &&
git reset --hard one &&
git fetch . left right &&
git merge --no-ff FETCH_HEAD &&
# one is ancestor of three (left) and four (right)
test_must_fail git rev-parse --verify HEAD^4 &&
git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
git rev-parse one three four | sort >expect &&
test_cmp expect actual
'
test_expect_success 'merge FETCH_HEAD octopus fast-forward (does not ff)' '
t3033_reset &&
git fetch . left right &&
git merge FETCH_HEAD &&
# two (master) is not an ancestor of three (left) and four (right)
test_must_fail git rev-parse --verify HEAD^4 &&
git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
git rev-parse two three four | sort >expect &&
test_cmp expect actual
'
test_expect_success 'merge FETCH_HEAD octopus non-fast-forward' '
t3033_reset &&
git fetch . left right &&
git merge --no-ff FETCH_HEAD &&
test_must_fail git rev-parse --verify HEAD^4 &&
git rev-parse HEAD^1 HEAD^2 HEAD^3 | sort >actual &&
git rev-parse two three four | sort >expect &&
test_cmp expect actual
'
# two-project merge
test_expect_success 'refuse two-project merge by default' '
t3033_reset &&
git reset --hard four &&
test_must_fail git merge five
'
test_expect_success 'two-project merge with --allow-unrelated-histories' '
t3033_reset &&
git reset --hard four &&
git merge --allow-unrelated-histories five &&
git diff --exit-code five
'
test_done