On Thu, Sep 22, 2016 at 2:49 PM, Nicholas Alexander <nalexan...@mozilla.com> wrote:
> > > On Thu, Sep 22, 2016 at 1:20 PM, Gregory Szorc <g...@mozilla.com> wrote: > >> For years it has been a common pattern for local builds and Firefox >> automation to copy test files to the object directory (or some other >> staging area) and run them from there. This creates several inefficiencies: >> >> * The build system must symlink or copy thousands of test related files >> during the build >> * Running tests requires checking if test files in the objdir are up to >> date (can add significant latency to the edit-test loop) >> * Builds in automation must create and upload archives containing >> thousands of test files >> * This makes it harder to skip build jobs if all that has changed is a >> test file >> * Test jobs in automation must download and extract archives containing >> test files >> * Test jobs in automation typically don't have access to a full source >> checkout and can't easily piggyback on existing infrastructure (such as >> mach commands, vendored Python packages, etc). This leads to wheel >> reinvention and inconsistency between local dev environments and automation. >> >> The historical reasons for doing things this way were valid. But with >> moz.build, other improvements to the build system, automation scheduling >> and configuration living in-tree, and better scaling of Mercurial in >> automation, these historical reasons are largely no longer valid. >> >> Going forward, I'm requesting we change our policy regarding tests and >> automation to be source checkout first. This means: >> >> * Tests should be designed to run from a source checkout with minimal >> "build" actions required (no file copying/symlinking, no preprocessing into >> a new file, etc) >> * Automation should run everything from a source checkout (as opposed to >> downloading archives containing files derived from source checkouts) >> >> Does anyone have any concerns or objections to this? >> > > This only makes sense for a subset of our harnesses. Tests that need to > be compiled (gtest?, Android unit and Robocop tests) can never achieve > this. So as long as we're clear that we want to remove preprocessing and > special mozharness-foo to work around packaging tests but we're not pushing > *everything* to source-only, I'm good. > The goal is to reduce the amount of work needed to run tests. You are correct that compiled tests inherently need a build step to run them and we can't simply run them from a source checkout. That being said, it isn't out of the question to defer the compilation of these tests to test jobs: the build job delays execution of nearly all tests and making the build job faster by moving work out of that job could make end-to-end times faster, even if we're doing extra work in individual test jobs (that have to compile tests). Historically, we didn't have a compiler available on test machines. But with TaskCluster+Docker and tooltool, it is much easier to put needed files on testers. So compiling tests on test machines is something we should consider.
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