x/tools/gopls: parameter movement bug bash

[findleyr]

This issue tracks bugs encountered while using the new change signature/parameter movement feature.
Aggregating into a single issue for convenience; I'll keep adding to this list as I encounter bugs.

• Unnecessary conversion between named and unnamed concrete types (example: passing type Hash [32]byte as an argument to a [32]byte parameter, we see that the inliner adds unnecessary conversions to [32]byte. I avoided unecessary interface->interface conversions, but we also don't need to worry about concrete->concrete.
• Given a call site involving a short variable declaration (x, y := Foo(1, 2)), the inliner thinks it needs to introduce a binding declaration for x, y.
• We offer to move variadic parameters... and then fail to type check the resulting modified package because we don't do it correctly. For now, we should not offer the parameter movement code action, if it involves a variadic parameter (my intuition is that supporting variadics would be too complicated to fix presently).
• The inliner is too conservative about side effects. For change signature refactoring, we should ignore effects.
• The rewrite used for change signature refactoring is liable to run into argument variables shadowed by other parameters. We can avoid this using shadow groups.

[gopherbot]

Change https://go.dev/cl/632115 mentions this issue: gopls/internal/test/marker: add reproducers for moveparam bug bash bugs

[findleyr]

(BTW, if anyone reading this is experimenting with the new parameter movement code action, please feel free to comment with any bugs you observe).

[gopherbot]

Change https://go.dev/cl/632935 mentions this issue: internal/refactor/inline: more precise redundant conversion detection

[gopherbot]

Change https://go.dev/cl/633096 mentions this issue: gopls/internal/golang: don't offer to move variadic parameters

[gopherbot]

Change https://go.dev/cl/632937 mentions this issue: internal/refactor/inline: fix condition for assignment splice strategy

[gopherbot]

Change https://go.dev/cl/633256 mentions this issue: internal/refactor/inline: substitute groups of codependent arguments

[gopherbot]

Change https://go.dev/cl/633255 mentions this issue: gopls/internal/golang: ignore effects for change signature refactoring