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"GODEBUG" is a mechanism that the Go runtime forces on OpenTofu that allows dynamic changes to various nuances of Go standard library behavior. We cannot control when GODEBUG workarounds are added and removed from Go, so if someone chooses to rely on them then they are likely to get broken by a later release of OpenTofu that uses a newer version of Go. Therefore we'd like anyone relying on these to tell us so we can try to find a more sustainable solution to their problem early on while the workaround is still available to them. We also occasionally force certain GODEBUG workarounds on by default in our official builds in anticipation of breakage caused by upstream Go changes. In that case we'd still like to know if anyone is relying on them so that we can remove those workarounds in a future release, but we'd prefer to get the reports about it in an issue or discussion we'd already created for that purpose. This therefore introduces warning diagnostics any time something in the "init", "plan", or "apply" commands relies on non-default GODEBUG settings. For ones we enabled intentionally we provide a specific URL to report usage as part of the diagnostic message, but we also have a generic message for any GODEBUG settings the user chose to enable for themselves for reasons we probably don't know about yet but would like to learn more about. This is included in only that subset of commands as a compromise because those are the commands most likely to interact with Go library features that are affected by these workarounds -- they most commonly affect functionality related to networking, TLS, etc -- and additional diagnostics in these locations should not to cause breakage for anyone consuming the machine-readable output, but there are other commands where additional diagnostics are more likely to cause problems. Unfortunately it isn't really possible to unit-test this because it relies directly on information reported by the Go metrics system and there's no facility to produce fake metrics for testing. However, Go 1.26 (which we're currently using) there is a GODEBUG setting "netedns0=0" which causes a warning any time OpenTofu makes a DNS request, so I've tested this manually by running "tofu init" with that workaround enabled in a configuration that depends on at least one provider (causing DNS lookups for the provider registry) and seen it generate the expected warning message referring to "netedns0". These new warnings replace our previous quieter messages about this in the TF_LOG=warn output, because those were only useful in situations where GODEBUG was causing a problem that led to someone opening a bug report, but we actually want to know of situations where GODEBUG was needed in order for OpenTofu to _succeed_ and so for that we need more prominent messages to let the operator know there's something they ought to report to us even though there wasn't an error. Signed-off-by: Martin Atkins <mart@degeneration.co.uk>