Add Go 1.20 errors.Join support

[dhartunian]

This PR contains the Join implementation from #106 and adds
some adjustments to fit the rest of the library's style.

We move the newly added Join implementation that mirrors
the go 1.20 stdlib function into a separate package like the rest of
our custom error types.

Some simple unit tests are added and Join wrappers are also
integrated into the datadriven formatting test. Our existing format
code for multi-cause errors is compatible with this new type which
allows us to remove the custom formatter from the implementation.

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Please review last 2 commits. First one is #115.

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This change is 

[knz]

May I suggest:

• move the new join.go to its sub-package join immediately in the 1st commit.
• ensure the joinError type also implements SafeFormatError. Then express Error/Format using that, using the model already set by other types.
• in the 2nd commit, make the top-level join Join point to a wrapper in package errutil that follows the example of Wrap and also automatically adds a call to WithStack.

Reviewable status: 0 of 18 files reviewed, all discussions resolved

[knz]

Also, for your consideration:

What about not adding a joinError type altogether, and instead construct an opaqueMultiErrorLeaf with all the formatting done upfront (in errutil)?

(This would need to use a redact.RedactableString)

Reviewable status: 0 of 18 files reviewed, all discussions resolved

[knz]

(maybe my last consideration is not so great - the opaque type's support for redactable strings is janky)

If you do not do that, consider adding a decoder for the new joinError type.

Reviewable status: 0 of 18 files reviewed, all discussions resolved

[dhartunian]

@knz PTAL

• added custom encoder/decoder for Join (based on API extended in latest update to add formatting for multi-cause errors #115)
• merged the two commits into 1 to put the Join impl where it needs to be
• added custom formatter
• added public API wrapper with stack

[knz]

CI is trying to tell you something.

I'd say let's merge #115 then you can rebase this which will make the review easier.

[dhartunian]

CI is trying to tell you something.

lol fixed 😄

[knz]

Reviewed 17 of 18 files at r5, 8 of 8 files at r6, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @dhartunian)

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go.mod line 3 at r6 (raw file):

module github.com/cockroachdb/errors

go 1.18

I'm not sure you wanted to change this?

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join/join.go line 76 at r6 (raw file):

func (e *joinError) SafeFormatError(p errbase.Printer) error {
	p.Print(e.Error())

Please do it the other way around: put the logic in here, then do Error() string { return redact.StringWithoutMarkers(e) }

Otherwise you'd be throwing redactability out of the window.

(you can see the effects of this in the format tests)

[dhartunian]

Reviewable status: 13 of 25 files reviewed, 2 unresolved discussions (waiting on @knz)

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go.mod line 3 at r6 (raw file):

Previously, knz (Raphael 'kena' Poss) wrote…

I'm not sure you wanted to change this?

whoops. done.

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join/join.go line 76 at r6 (raw file):

Previously, knz (Raphael 'kena' Poss) wrote…

Please do it the other way around: put the logic in here, then do Error() string { return redact.StringWithoutMarkers(e) }

Otherwise you'd be throwing redactability out of the window.

(you can see the effects of this in the format tests)

done.

[knz]

💯

Reviewed 12 of 12 files at r7, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dhartunian)