This includes the addition of the new "//go:build" comment form in addition
to the legacy "// +build" notation, as produced by gofmt to ensure
consistent behavior between Go versions. The new directives are all
equivalent to what was present before, so there's no change in behavior.
Go 1.17 continues to use the Unicode 13 tables as in Go 1.16, so this
upgrade does not require also upgrading our Unicode-related dependencies.
This upgrade includes the following breaking changes which will also
appear as breaking changes for Terraform users, but that are consistent
with the Terraform v1.0 compatibility promises.
- On MacOS, Terraform now requires macOS 10.13 High Sierra or later.
This upgrade also includes the following breaking changes which will
appear as breaking changes for Terraform users that are inconsistent with
our compatibility promises, but have justified exceptions as follows:
- cidrsubnet, cidrhost, and cidrnetmask will now reject IPv4 CIDR
addresses whose decimal components have leading zeros, where previously
they would just silently ignore those leading zeros.
This is a security-motivated exception to our compatibility promises,
because some external systems interpret zero-prefixed octets as octal
numbers rather than decimal, and thus the previous lenient parsing could
lead to a different interpretation of the address between systems, and
thus potentially allow bypassing policy when configuring firewall rules
etc.
This upgrade also includes the following breaking changes which could
_potentially_ appear as breaking changes for Terraform users, but that do
not in practice for the reasons given:
- The Go net/url package no longer allows query strings with pairs
separated by semicolons instead of ampersands. This primarily affects
HTTP servers written in Go, and Terraform includes a special temporary
HTTP server as part of its implementation of OAuth for "terraform login",
but that server only needs to accept URLs created by Terraform itself
and Terraform does not generate any URLs that would be rejected.
ioutil.TempFile has a special case where an empty string for its dir
argument is interpreted as a request to automatically look up the system
temporary directory, which is commonly /tmp .
We don't want that behavior here because we're specifically trying to
create the temporary file in the same directory as the file we're hoping
to replace. If the file gets created in /tmp then it might be on a
different device and thus the later atomic rename won't work.
Instead, we'll add our own special case to explicitly use "." when the
given filename is in the current working directory. That overrides the
special automatic behavior of ioutil.TempFile and thus forces the
behavior we need.
This hadn't previously mattered for earlier callers of this code because
they were creating files in subdirectories, but this codepath was failing
for the dependency lock file due to it always being created directly
in the current working directory.
Unfortunately since this is a picky implementation detail I couldn't find
a good way to write a unit test for it without considerable refactoring.
Instead, I verified manually that the temporary filename wasn't in /tmp on
my Linux system, and hope that the comment inline will explain this
situation well enough to avoid an accidental regression in future
maintenence.
This originated in the cliconfig code to write out credentials files. The
Windows implementation of this in particular was quite onerous to get
right because it needs a very specific sequence of operations to avoid
running into exclusive file locks, and so by factoring this out with
only cosmetic modification we can avoid repeating all of that engineering
effort for other atomic file writing use-cases.
Martin Atkins