tree 39d352c8539df2f0e771d8074155a16b6eb74f28
parent 918e96ac795f6d9de2d0b487826297420e899e3f
author Rob Findley <rfindley@google.com> 1696364616 -0400
committer Gopher Robot <gobot@golang.org> 1697466449 +0000

gopls/internal/lsp: add code actions to remove unused parameters

Use the new inlining technology to implement a first change-signature
refactoring, by rewriting the declaration to be a trivial wrapper around
a declaration with modified signature, inlining the wrapper, and then
performing string substitution to replace references to the synthetic
delegate.

This demonstrates the power of inlining, which can be seen as a more
general tool for rewriting source code: express old code as new code,
recognize instances of old code (in this case, calls), and inline.

However, this CL was still rather difficult, primarily because of (1)
the problem of manipulating syntax without breaking formatting and
comments, and (2) the problem of composing multiple refactoring
operations, which in general requires iterative type checking.

Neither of those difficulties have general solutions: any form of
nontrivial AST manipulation tends to result in an unacceptable movement
of comments, and iterative type checking is difficult because it may
involve an arbitrarily modified package graph, and because it is
difficult to correlate references in the previous version of the package
with references in the new version of the package.

But in the case of removing a parameter, these problems are solvable: We
can avoid most AST mangling by restricting the scope of rewriting to the
function signature. We can type check the new package using the imports
of the old package. We can find the next reference in the new package by
counting.

Fixes golang/go#63534

Change-Id: Iba5fa6b0da503b7723bea1b43fd2c4151576a672
Reviewed-on: https://go-review.googlesource.com/c/tools/+/532495
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Findley <rfindley@google.com>