feat: add a Gno2Go precompiler

[moul]

This PR is a proposal for https://github.com/gnolang/bounties#10-use-go-typechecker

Official target:

• Rename .go to .gno where appropriate
• Make gno precompiler (which comes before preprocessor) compile .gno to .go in same folder.
• "gno.land/r/realm" in .gno becomes "github.com/gnolang/gno/examples/gno.land/r/realm" in .go.
• "std" becomes "github.com/gnolang/gno/stdlibs/stdshim" (?)
• keeps a whitelist of stdlib packages (to prevent attacks, to prevent compiling malware).
• Precompiler tries to compile the translated .go code using go, before proceeding.

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My plan/implementation:

• implement a transformation system in the gno.Gno2Go func.
• replace std with github.com/gnolang/gno/stdlibs/stdshim.
• replace gno.land/r/realm with github.com/gnolang/gno/examples/gno.land/r/realm.
• always add a top-level comment to indicate that the .go files was generated (in case someone commits the generated files).
• removed tests/go.mod, no you can safely run go test -v ./... from the top-level directory.
• because ./stdlibs/* is both used by the .gno files and also by some .go files, I decided to rename them to .gno and create symlinks for each files so that go test ./... can work.
• initial version of a gnodev tool with gnodev precompile ./path/to/package
• bootstrap a simple stdshim package.
• way to ensure the go version we're checking against, for distributed determinism. (feat: add a Gno2Go precompiler #119 (comment))

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Also, I’ve a suggestion: what do about creating a new cmd/gnodev command, dedicated to contract developers, with tools like precompile, test and other developer tools?
That’s personally what I would love to work with.

Note: the PR is pretty big, because it renames a lot of .go files to .gno; the interesting files here are gno2go{,_test}.go.

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Fixes #107
Related with #121
Closes #113 (replace)

[jaekwon]

thank you @moul, this looks awesome, though i've yet to read the code yet. I will review by tomorrow when I'm back.
cmd/gnodev command sounds great.
I noticed that in the last commit, git didn't seem to register that many of the files were renamed. Can that be fixed, to preserve file history of the original .go files?

[moul]

I noticed that in the last commit, git didn't seem to register that many of the files were renamed. Can that be fixed, to preserve file history of the original .go files?

Sure thing, I'll create a commit for the git mv and another one for the porting changes.

[moul]

I'm not sure why, but even with a dedicated commit for moving, and another one for fixing, GitHub seems to make shortcuts and only look the general diff with master.

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here it works (probably because the change is small)

here it doesn't work

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Any suggestions?

[moul]

New: an initial version of gnodev.

[jaekwon]

looks good so far... we probably also want a way to ensure the go version we're checking against, for distributed determinism.

[moul]

looks good so far... we probably also want a way to ensure the go version we're checking against, for distributed determinism.

I added it in the list of checkboxes at the top of the PR, so we can remind to do them in a new one.

[jaekwon]

Merging in to prevent conflicts; another PR will complete the precompile logic. Thank you @moul.