Related #29452. I think we need to make a decision on what side effects go list should have before changing.

I believe this is currently working as designed. cmd/go saves information to go.mod so that commands are reproducible (including go list). This is not what many people expect of go list though.

@jayconrod is it the same issue, though? Note that @rogpeppe had the module in question already as a requirement, since go mod tidy was run. In fact, re-running tidy is removing the extra indirect lines once again. I don't think this is simply a "list should have no side effects" issue.

@mvdan I think it's the same issue. The main module depends on the package github.com/btcsuite/btcutil/base58, which has no dependencies outside the standard library. go list github.com/btcsuite/btcutil adds the transitive dependencies of that package. go mod tidy removes those dependencies, since nothing in the main module transitively depends on them.

go mod tidy effectively acts like a garbage collector: it removes requirements on modules which are unreachable from packages in the main module.

#29452 is related but distinct.

#26977 is probably the same underlying problem. Arguably both go mod why and go list (without -versions) should avoid resolving the requested package unless it is already in some module in the build list.

Hmm, this isn't quite the same as #26977 either: in this case, the package in question is already in an active module, but that module's dependencies have not been resolved.

go list resolves those dependencies as a side-effect of loading the package, but since you didn't actually request any information about the package's imports, we arguably don't need to load them. (See also #29666.)

On further consideration, I think this is more-or-less a duplicate of #29666.

In contrast, if you had asked for any substantial information about the dependencies of github.com/btcsuite/btcutil (for example, by examining the ImportMap field using -f '{{.ImportMap}}' or -json), then the go tool should arguably add the corresponding version information to the go.mod file to ensure that the output of the command is reproducible.