x/build: "gomin" builders that test golang.org/x modules at their minimum Go toolchain version (using linux/amd64 only to start with)

[dmitshur]

This new-builder issue is a new opportunity enabled by work in #69095: it relies on golang.org/x modules now always having a requirement on a supported Go toolchain version. It is also based on findings from issue #67749.

This new "gomin" builder type applies only to x/ repos, and it extends the current version dimension each builder has. For example, in addition to x_tools-gotip-linux-amd64, x_tools-go1.25-linux-amd64, x_tools-go1.25-linux-amd64, there would also be a "x_tools-gomin-linux-amd64" builder. The aforementioned existing builders test all applicable x/tools modules with a Go toolchain built from latest commit on the master, release-branch.go1.25, and release-branch.go1.24 branches, respectively. The gomin builder would iterate over each module, determine the minimum Go toolchain required, and test with that Go toolchain version.

The intention of the builder is to cover another end the minor version spectrum, and potentially catch issues that the "latest commit on release branch" builders would not catch. Such issues can be resolved in the modules themselves, or if deemed worthwhile, by carefully increasing the go directive to require a specific minor version. See CL 640036 and CL 662036 for past examples.

CC @golang/release, @findleyr, @adonovan.

[gabyhelp]

Related Issues

• x/build: add a builder that runs long tests with a gccgo toolchain #35786

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