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[104.178.186.189]) by smtp.gmail.com with ESMTPSA id a16-20020a027350000000b0038a08d5ac32sm6753525jae.31.2022.12.06.17.31.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Dec 2022 17:31:02 -0800 (PST) Date: Tue, 6 Dec 2022 20:31:01 -0500 From: Taylor Blau To: Johannes Schindelin via GitGitGadget Cc: git@vger.kernel.org, =?utf-8?B?UmVuw6k=?= Scharfe , =?utf-8?B?w4Z2YXIgQXJuZmrDtnLDsA==?= Bjarmason , Johannes Schindelin Subject: Re: [PATCH v5 2/2] tests(mingw): avoid very slow `mingw_test_cmp` Message-ID: References: <6a80fab7e3936ec56e1583d6136d47487327e907.1670339267.git.gitgitgadget@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <6a80fab7e3936ec56e1583d6136d47487327e907.1670339267.git.gitgitgadget@gmail.com> Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Hi Johannes, On Tue, Dec 06, 2022 at 03:07:47PM +0000, Johannes Schindelin via GitGitGadget wrote: > Learning the lesson to avoid shell scripting wherever possible, the Git > for Windows project implemented a minimal replacement for > `mingw_test_cmp` in the form of a `test-tool` subcommand that parses the > input files line by line, ignoring line endings, and compares them. > Essentially the same thing as `mingw_test_cmp`, but implemented in > C instead of Bash. This solution served the Git for Windows project > well, over years. > > However, when this solution was finally upstreamed, the conclusion was > reached that a change to use `git diff --no-index` instead of > `mingw_test_cmp` was more easily reviewed and hence should be used > instead. > > The reason why this approach was not even considered in Git for Windows > is that in 2007, there was already a motion on the table to use Git's > own diff machinery to perform comparisons in Git's test suite, but it > was dismissed in https://lore.kernel.org/git/xmqqbkrpo9or.fsf@gitster.g/ > as undesirable because tests might potentially succeed due to bugs in > the diff machinery when they should not succeed, and those bugs could > therefore hide regressions that the tests try to prevent. > > By the time Git for Windows' `mingw-test-cmp` in C was finally > contributed to the Git mailing list, reviewers agreed that the diff > machinery had matured enough and should be used instead. > > When the concern was raised that the diff machinery, due to its > complexity, would perform substantially worse than the test helper > originally implemented in the Git for Windows project, a test > demonstrated that these performance differences are well lost within the > 100+ minutes it takes to run Git's test suite on Windows. Thanks for this update. I think these five paragraphs are an accurate and helpful record of the history behind this patch and approach. It is very much appreciated. Thanks, Taylor