x/tools/go/packages: Load(&cfg...) modifies cfg, contra explicit documentation

[adonovan]

The Load function claims not to mutate the Config, but it does in fact mutate the non-exported fields, and has done for some time. In https://go.dev/cl588936 I proposed to update the docs to match reality:

// Calls to [Load] do not modify the public fields of this struct, but
// may modify hidden fields, so concurrent calls to [Load] must not
// use the same Config.

but perhaps we should instead reestablish the invariant rather than give it up.

@findleyr @matloob

[gopherbot]

Change https://go.dev/cl/625255 mentions this issue: go/packages: remove unexported fields from user facing Config

[xieyuschen]

Hi @adonovan , I have sent you a CL by moving all unexport fields from Config to an unexported config struct so packages.Load won't modify user provided Config in any case. Let me know whether you like this approach:)

[gopherbot]

Change https://go.dev/cl/625475 mentions this issue: go/packages: do not mutate Config