x/tools: rewrite git history to remove accidental merge commit

[stamblerre]

Over the holidays, I accidentally merged golang/tools@2152f4e and then tried to revert it with golang/tools@6375436. This caused the gopls pseudoversions to start with v0.6.2 rather than v0.0.0 as before. We need to rewrite the Git history to remove these commits and restore the original pseudoversions.

[cagedmantis]

/cc @golang/release

[dmitshur]

We needed to rewrite the history of x/tools master branch so that the gopls/v0.6.1 tag would no longer be an ancestor (this is what was causing the pseudo-versions to start with v0.6.2-0.).

This is now done. The previous master commit golang/tools@e2f9c7f was replaced with commit golang/tools@1b1bb64, which prunes the merge CL and its revert but keeping the tree content unmodified.

Here's the complete log of how the rewrite was generated, for posterity:

$ cd $(mktemp -d)
$ git clone https://go.googlesource.com/tools && cd tools
Cloning into 'tools'...
[...]
tools $ git checkout master
Already on 'master'
Your branch is up to date with 'origin/master'.
tools $ git rev-parse HEAD
e2f9c7f1fc8e3456c71ab5b45a8220d3ae8e0aef
tools $ git merge-base --is-ancestor gopls/v0.6.1 HEAD && echo "problem" || echo "ok"
problem
tools $ git checkout -b rewrite-master master       
Switched to a new branch 'rewrite-master'
tools $ git diff master

# Rebase (interactively) on top of the latest commit on master
# branch before the merge CL.
tools $ git rebase -i 4a19ffb6e6422ea8855acc6b07cac1c44aa814e7

    (use this rebase script)

    # Rebase 4a19ffb6..e2f9c7f1 onto 4a19ffb6 (27 commands)
    #
    # Commands:
    # x, exec <command> = run command (the rest of the line) using shell
    # ...
    #
    # These lines can be re-ordered; they are executed from top to bottom.
    #
    # If you remove a line here THAT COMMIT WILL BE LOST.

    # Drop the merge of gopls-release-branch.0.6 and its commits.
    #pick 72fbef54 internal/lsp/debug: update version number for v0.6.0
    #pick 2037813f gopls: update go.mod for v0.6.0-pre.1
    #pick c88dec5c [gopls-release-branch.0.6] internal/lsp: add titles to `go mod tidy` and update go.sum fixes
    #pick 1eed4871 gopls: update go.mod for gopls/v0.6.1-pre.1

    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' ee6d6aff)" git cherry-pick ee6d6aff # internal/lsp: restructure user options (CL 278433 continued)
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 0af0626a)" git cherry-pick 0af0626a # internal/lsp: save all possible keys for analyses, codelenses
    
    # Drop the revert.
    #pick 63754364 Revert "[gopls-release-branch.0.6] all: merge master into gopls-release-branch.0.6"
    
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 2dba1e4e)" git cherry-pick 2dba1e4e # go/analysis/passes/fieldalignment: add command
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 773b96fa)" git cherry-pick 773b96fa # internal/lsp: avoid panic during interface assertion
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' d8d6ddbe)" git cherry-pick d8d6ddbe # cmd/goyacc: double ACTSIZE, NSTATE and TEMPSTATE
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' b0ab187a)" git cherry-pick b0ab187a # gopls/internal/regtest: support multiple workspace folders
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 5e19fbb8)" git cherry-pick 5e19fbb8 # gopls: bump gofumpt to v0.1.0
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 79627818)" git cherry-pick 79627818 # gopls/doc: add additional information on CI in contributing.md
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' a548c3f4)" git cherry-pick a548c3f4 # gopls: update link to nvim-lspconfig gopls configuration
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' c658f992)" git cherry-pick c658f992 # internal/lsp/source: return all field funcs from outgoing callhierarchy
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 9ed45478)" git cherry-pick 9ed45478 # go/packages: remove -mod, -modfile flags from build flags for go version
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 465c416c)" git cherry-pick 465c416c # all: add copyright notices to files that are missing them
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' f9b4b89a)" git cherry-pick f9b4b89a # gopls/internal/regtest: skip regtests on android-amd64-emu
    
    # This CL is being dropped because it's no longer needed:
    # The change it makes is already in tree. It was fixing up
    # a change that the merge introduced, which is backed out.
    #pick 63752411 internal/lsp/debug: change hardcoded version to a constant
    
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 113979e3)" git cherry-pick 113979e3 # internal/lsp/cache: fix module paths in nested module error messages
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' a85a8cee)" git cherry-pick a85a8cee # internal/lsp/cache: fix panic in GOPATH mode
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 4ed967dd)" git cherry-pick 4ed967dd # Revert "go/analysis/passes/structtag: recognize multiple keys per tag"
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' a008e46a)" git cherry-pick a008e46a # gopls: use standard command doc comment format
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 551e49d8)" git cherry-pick 551e49d8 # gopls/internal/regtest: fix TestUnimportedCompletions
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' 7339b064)" git cherry-pick 7339b064 # gopls/internal/hooks: create included licenses text
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' e9a2c070)" git cherry-pick e9a2c070 # internal/lsp/cmd: add licenses command
    x GIT_COMMITTER_DATE="$(git show -s --pretty='%cd' e2f9c7f1)" git cherry-pick e2f9c7f1 # gopls/doc/emacs.md: describe configuration for eglot

Successfully rebased and updated refs/heads/rewrite-master.
tools $ git merge-base --is-ancestor gopls/v0.6.1 HEAD && echo "problem" || echo "ok"
ok
tools $ git diff master
tools $

Notably:

• the unwanted gopls/v0.6.1 tag is no longer an ancestor of master branch
• committer dates were preserved (since pseudo-versions use those)
• the result is an identical tree as the original x/tools master

This issue is resolved now, and doing go get of the latest master commit (directly to VCS, bypassing module mirror for testing purposes) gives a v0.0.0 pseudo-version:

$ GO111MODULE=on GOPROXY=direct GOSUMDB=off go list -m -json golang.org/x/tools/gopls@master
{
	"Path": "golang.org/x/tools/gopls",
	"Version": "v0.0.0-20210108195828-1b1bb6453dc0",
	"Time": "2021-01-08T19:58:28Z"
}

In order to keep the previously published x/tools pseudo-versions valid, we created a new branch internal-branch.issue43628 that points to the previous x/tools master commit.

This works too:

$ GO111MODULE=on GOPROXY=direct GOSUMDB=off go list -m -json golang.org/x/tools@v0.0.0-20210108195828-e2f9c7f1fc8e 
{
	"Path": "golang.org/x/tools",
	"Version": "v0.0.0-20210108195828-e2f9c7f1fc8e",
	"Time": "2021-01-08T19:58:28Z"
}

I'll send a mail to golang-dev@ to notify anyone working on x/tools that a rewritten history is expected. No CLs were dropped during the rewrite and force push, so nothing needs to be re-sent. Closing.

[FiloSottile]

One more for #26201.