[PATCH jn/test-lint-one-shot-export-to-shell-function] fetch test: mark test of "skipping" haves as v0-only

Since 633a53179e (fetch test: avoid use of "VAR= cmd" with a shell function, 2019-12-26), t5552.5 (do not send "have" with ancestors of commits that server ACKed) fails when run with GIT_TEST_PROTOCOL_VERSION=2.

The cause:

The progression of "have"s sent in negotiation depends on whether we are using a stateless RPC based transport or a stateful bidirectional one (see for example 44d8dc54e7, "Fix potential local deadlock during fetch-pack", 2011-03-29). In protocol v2, all transports are stateless transports, while in protocol v0, transports such as local access and ssh are stateful.

In stateful transports, the number of "have"s to send multiplies by two each round until we reach PIPESAFE_FLUSH (that is, 32), and then it increases by PIPESAFE_FLUSH each round. In stateless transport, the count multiplies by two each round until we reach LARGE_FLUSH (which is 16384) and then multiplies by 1.1 each round after that.

Moreover, in stateful transports, as fetch-pack.c explains:

	We keep one window "ahead" of the other side, and will wait
	for an ACK only on the next one.

This affects t5552.5 because it looks for "have"s from the negotiator that appear in that second window. With protocol version 2, the second window never arrives, and the test fails.

Until 633a53179e (2019-12-26), a previous test in the same file contained

	GIT_TEST_PROTOCOL_VERSION= trace_fetch client origin to_fetch

In many common shells (e.g. bash when run as "sh"), the setting of GIT_TEST_PROTOCOL_VERSION to the empty string lasts beyond the intended duration of the trace_fetch invocation. This causes it to override the GIT_TEST_PROTOCOL_VERSION setting that was passed in to the test during the remainder of the test script, so t5552.5 never got run using protocol v2 on those shells, regardless of the GIT_TEST_PROTOCOL_VERSION setting from the environment. 633a53179e fixed that, revealing the failing test.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
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Junio C Hamano wrote:

Here's the promised fix, against jn/test-lint-one-shot-export-to-shell-function. Thanks again.

 t/t5552-skipping-fetch-negotiator.sh | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)