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Michael Anthony Knyszek 1634fde4f9 iter: don't iterate if stop is called before next on Pull
Consider the following code snippet:

    next, stop := iter.Pull(seq)
    stop()

Today, seq will iterate exactly once before it notices that its
iteration is invalid to begin with. This effect is observable in a
variety of ways. For example, if the iterator panics, since that panic
must propagate to the caller of stop. But if the iterator is stateful in
anyway, then it may update some state.

This is somewhat unexpected and because it's observable, can be depended
upon. This behavior does not align well with other possible
implementations of Pull, like CPS performed by the compiler. It's also
just odd to let even one iteration happen, precisely because of
unexpected state modification.

Fix this by not iterating at all of the done flag is set before entering
the iterator.

For #67712.

Change-Id: I18162e29df45a2e8968f68379450d92e1de47c4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/590075
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Austin Clements <austin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
2024-06-07 19:09:28 +00:00
.github .github/ISSUE_TEMPLATE/03-gopls.yml: use textarea for gopls version 2024-05-24 17:09:04 +00:00
api api: promote next to go1.23 2024-06-05 20:48:49 +00:00
doc doc: document new default for GODEBUG gotypesalias setting in release notes 2024-06-05 21:30:00 +00:00
lib/time lib/time: use consistent directory in mkzip usage message 2024-03-04 17:32:07 +00:00
misc misc/wasm: drop wasmtime < 14 support 2024-04-11 17:09:10 +00:00
src iter: don't iterate if stop is called before next on Pull 2024-06-07 19:09:28 +00:00
test cmd/compile/ssa: fix (MOVWZreg (RLWINM)) folding on PPC64 2024-06-07 19:02:52 +00:00
.gitattributes all: treat all files as binary, but check in .bat with CRLF 2020-06-08 15:31:43 +00:00
.gitignore internal/platform,cmd/dist: export the list of supported platforms 2023-06-22 19:44:52 +00:00
codereview.cfg codereview.cfg: add codereview.cfg for master branch 2021-02-19 18:44:53 +00:00
CONTRIBUTING.md doc: normalize proposal-process links 2023-03-29 22:00:27 +00:00
go.env cmd/go: additional doc-inspired tests and bug fixes 2023-06-06 19:18:46 +00:00
LICENSE doc: revert copyright date to 2009 2016-06-01 22:40:04 +00:00
PATENTS LICENSE: separate, change PATENTS text 2010-12-06 16:31:59 -05:00
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SECURITY.md SECURITY.md: update the Reporting a Vulnerability link 2023-09-22 21:17:24 +00:00

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