git-checkout: improve error messages, detect ambiguities.

The patch is twofold: it moves the option consistency checks just under
the parse_options call so that it doesn't get in the way of the tree
reference vs. pathspecs desambiguation.

The other part rewrites the way to understand arguments so that when
git-checkout fails it does with an understandable message. Compared to the
previous behavior we now have:

  - a better error message when doing:

        git checkout <blob reference> --

    now complains about the reference not pointing to a tree, instead of
    things like:

        error: pathspec <blob reference> did not match any file(s) known to git.
        error: pathspec '--' did not match any file(s) known to git.

  - a better error message when doing:

        git checkout <path> --

    It now complains about <path> not being a reference instead of the
    completely obscure:

        error: pathspec '--' did not match any file(s) known to git.

  - an error when -- wasn't used, and the first argument is ambiguous
    (i.e. can be interpreted as both ref and as path).

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/t/t2010-checkout-ambiguous.sh b/t/t2010-checkout-ambiguous.sh
new file mode 100755
index 0000000000..7cc0a3582e
--- /dev/null
+++ b/t/t2010-checkout-ambiguous.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+test_description='checkout and pathspecs/refspecs ambiguities'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo hello >world &&
+	echo hello >all &&
+	git add all world &&
+	git commit -m initial &&
+	git branch world
+'
+
+test_expect_success 'reference must be a tree' '
+	test_must_fail git checkout $(git hash-object ./all) --
+'
+
+test_expect_success 'branch switching' '
+	test "refs/heads/master" = "$(git symbolic-ref HEAD)" &&
+	git checkout world -- &&
+	test "refs/heads/world" = "$(git symbolic-ref HEAD)"
+'
+
+test_expect_success 'checkout world from the index' '
+	echo bye > world &&
+	git checkout -- world &&
+	git diff --exit-code --quiet
+'
+
+test_expect_success 'non ambiguous call' '
+	git checkout all
+'
+
+test_expect_success 'allow the most common case' '
+	git checkout world &&
+	test "refs/heads/world" = "$(git symbolic-ref HEAD)"
+'
+
+test_expect_success 'check ambiguity' '
+	test_must_fail git checkout world all
+'
+
+test_expect_success 'disambiguate checking out from a tree-ish' '
+	echo bye > world &&
+	git checkout world -- world &&
+	git diff --exit-code --quiet
+'
+
+test_done