For #46477.
Change-Id: Id02d8f67fe82228bab3f26b1cb4ebd6ee67c4634
Reviewed-on: https://go-review.googlesource.com/c/go/+/616816
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
The existing prose for struct identity did only require that two structs
"have the same sequence of fields, and if corresponding fields have the
same names, and identical types, and identical tags" for the structs to
be identical.
The implementation (forever) has also required that two corresponding
fields are either both embedded or not embedded. This is arguably part
of a struct's structure but is not explicitly specified.
This CL makes a minor change to the prose to address that.
Fixes#69472.
Change-Id: Ifa4ca69717986675642a09d03ce683ba8235efcb
Reviewed-on: https://go-review.googlesource.com/c/go/+/616697
Reviewed-by: Rob Pike <r@golang.org>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
The spec says that an embedded field must be specified
as a type name (or a pointer to a type name). This is
explicit in the prose and the FieldDecl syntax.
However, the prose on promoted methods required a named
type (originally the term used for a "defined type").
Before the introduction of alias types, type names could
only refer to named/defined types, so the prose was ok.
With the introduction of alias types in Go 1.9, we
distinguished between defined types (i.e., types given
a name through a type declaration) and type aliases
(types given an alternative name), and retired the notion
of a named type since any type with a name (alias type
and defined type) could be considered a "named type".
To make things worse, with Go 1.18 we re-introduced the
notion of a named type which now includes predeclared
types, defined types, type parameters (and with that
type aliases denoting named types).
In the process some of the wording on method promotion
didn't get updated correctly. At attempt to fix this
was made with CL 406054, but while that CL's description
correctly explained the intent, the CL changed the prose
from "defined type" to "named type" (which had the new
meaning after Go 1.18), and thus did not fix the issue.
This CL fixes that fix by using the term "type name".
This makes the prose consistent for embedded types and
in turn clarifies that methods of embedded alias types
(defined or not) can be promoted, consistent with the
implementation.
While at it, also document that the type of an embedded
field cannot be a type parameter. This restriction has
been in place since the introduction of type parameters
with Go 1.18 and is enforced by the compiler.
Fixes#66540.
For #41687.
Change-Id: If9e6a03d7b84d24a3e6a5ceda1d46bda99bdf1f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/603958
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Axel Wagner <axel.wagner.hh@googlemail.com>
Also add a missing table entry to the language versions section in the
appendix.
Fixes#67977.
Change-Id: I1f98abbbcc34a4ff31f390752635435eaf6120b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/592595
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
For #65236.
Change-Id: I5a11811cc52467ea4446db29c3f86b119f9b2409
Reviewed-on: https://go-review.googlesource.com/c/go/+/592295
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
For #65237.
Change-Id: Id38747efebd46633f453eadaf68d818064faa778
Reviewed-on: https://go-review.googlesource.com/c/go/+/590396
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
For #61405.
Fixes#65237.
Change-Id: Ia7820c0ef089c828ea7ed3d2802c5185c945290e
Reviewed-on: https://go-review.googlesource.com/c/go/+/589397
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Clarify that the range expression of a "for" loop is called *just* once to
rule out that it might be re-evaluated after each iteration.
Change-Id: Iedb61cd29e5238ac0168b8ac01c34d6208cc4312
Reviewed-on: https://go-review.googlesource.com/c/go/+/582775
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Fixes#66967.
Change-Id: I7b9d62dcb83bad60b2ce74e2e2bf1a36c6a8ae38
Reviewed-on: https://go-review.googlesource.com/c/go/+/581256
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
If the range expression is a numeric constant, the
range expression is also not evaluated.
Change-Id: I97201e5c136d3d1a87ed1500b19b7199b30bc9ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/581298
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
There is no hyphen between the organization and the number.
For example, https://standards.ieee.org/ieee/754/6210/
shows the string "IEEE 754-2019" and not "IEEE-754-2019".
This assists in searching for "IEEE 754" in documentation
and not missing those using "IEEE-754".
Change-Id: I9a50ede807984ff1e2f17390bc1039f6a5d162e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/575438
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Add unclosed HTML tags and remove redundant </a> tags.
Change-Id: I3fffbcfd640001c9cc4f6085150344daa0c4369b
Reviewed-on: https://go-review.googlesource.com/c/go/+/568155
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: shuang cui <imcusg@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
While at it, set the date to the Go 1.22 release date.
Change-Id: I03872626e500433eb63786d24c67810c8c6289f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/562337
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Also: report language version (plus date) in spec header.
Fixes#65137.
Change-Id: I4f1d220d5922c40a36264df2d0a7bb7cd0756bac
Reviewed-on: https://go-review.googlesource.com/c/go/+/557596
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Follow-up on CL 551095.
For #56010.
Change-Id: I8913d6ca96c419c81683e88c6286b05ae1323416
Reviewed-on: https://go-review.googlesource.com/c/go/+/552915
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
For #56010.
Change-Id: Icca987a03d80587dd0e901f596ff7788584893ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/551095
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Add a new section to the Appendix describing what features were
changed or added in which language version.
Add short links with references to the required language version
where relevant.
Fixes#63857.
Change-Id: I5250f856d8688a71602076fcc662aa678d96a5d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/549518
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Rob Pike <r@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
The valid conversions consider the core types of operands, not just
their underlying type.
This also explains the valid arguments for unsafe.Slice which are
explained in terms of unsafe.Pointer conversions.
unsafe.SliceData simply refers to "slice argument" and we use
similar terminology elsewhere in the spec to denote values that
have a core type of slice (or any other type for that matter).
Leaving alone for now.
Fixes#64452.
Change-Id: I0eed3abbc0606f22358835e5d434f026fe0909c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/551379
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
This CL is partly based on CL 510535.
For #61405.
Change-Id: Ic94f6726f9eb34313f11bec7b651921d7e5c18d4
Reviewed-on: https://go-review.googlesource.com/c/go/+/538859
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Fixes#63525.
Change-Id: Ie9aa4dd47c025cd593e576c6e8de1774e1d1e302
Reviewed-on: https://go-review.googlesource.com/c/go/+/535775
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
This CL clarifies the order of evaluation of the binary logical
operators, && and ||. The clarified semantics matches what cmd/compile
and x/tools/go/ssa already implement, and prohibit some optimizations
that are arguably allowed today but risk surprising users.
First, it specifies that the left operand is evaluated before the
right operand. This prohibits "(f() || true) && *p" from evaluating
"*p" before "f()".
Second, it specifies that binary logical operations are also ordered
lexically left-to-right with regard to function calls and receive
operations. This prohibits "h(*p || true || f(), g())" from evaluating
"*p" after "g()".
Finally, the "order of evaluation of [...] is not specified" wording
in the example is clarified to acknowledge that there are still some
other orderings that are implied lexically; e.g., x must be evaluated
and indexed before g(), and z now must be evaluated before h(). (Note:
Whether z is evaluated before or after f() remains unspecified, as
there's no lexical dependency.)
Change-Id: I9d316a7f1fbc83be663e116380a2cc7a4ace623d
Reviewed-on: https://go-review.googlesource.com/c/go/+/522938
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
The example text below suggests that []byte("") always evaluates to
the non-nil value []byte{}, but the text proper doesn't explicitly
require that. This CL makes it clear that it must not evaluate to
[]byte(nil), which otherwise was allowed by the wording.
Change-Id: I6564bfd5e2fd0c820d9b55d17406221ff93ce80c
Reviewed-on: https://go-review.googlesource.com/c/go/+/521035
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Change-Id: I40595a3f598483d029473af465c756f8777ecc91
Reviewed-on: https://go-review.googlesource.com/c/go/+/520915
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Irrespective of whether unification is exact or inexact, method
signatures of interfaces must always match exactly: a type never
satisfies/implements an interface if relevant method signatures
are different (i.e., not identical, possibly after substitution).
This change matches the fix https://go.dev/cl/519435.
For #61879.
Change-Id: I28b0a32d32626d85afd32e107efce141235a923d
Reviewed-on: https://go-review.googlesource.com/c/go/+/519455
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Change-Id: I06345199ff16c80be83c345d734caef1714ec089
Reviewed-on: https://go-review.googlesource.com/c/go/+/515338
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Change-Id: I0d4ccbc396c48d565c0cbe93c9558ab330a44d02
Reviewed-on: https://go-review.googlesource.com/c/go/+/513275
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
This leaves the specific unification details out in favor
of a (forthcoming) section in an appendix.
Change-Id: If984c48bdf71c278e1a2759f9a18c51ef58df999
Reviewed-on: https://go-review.googlesource.com/c/go/+/507417
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Change-Id: I9cdb301163b67add39928c8fc7df2b7f3893f45e
Reviewed-on: https://go-review.googlesource.com/c/go/+/511836
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
The new section describes type inference as the problem
of solving a set of type equations for bound type parameters.
The next CL will update the section on unification to match
the new inference approach.
Change-Id: I2cb49bfb588ccc82d645343034096a82b7d602e2
Reviewed-on: https://go-review.googlesource.com/c/go/+/503920
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Per feedback on #56351.
For #56351.
Change-Id: I63dd1713a1efe4d7180d932dbd8e1510cbb32e90
Reviewed-on: https://go-review.googlesource.com/c/go/+/510935
TryBot-Bypass: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Change-Id: I9f008dba7ba6e30f0e62647482a3ed0b51bc1ad0
Reviewed-on: https://go-review.googlesource.com/c/go/+/502997
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Fixes#60731.
Change-Id: I71fad1c8385b13d036bb0ce7ae6bd21e0f596e51
Reviewed-on: https://go-review.googlesource.com/c/go/+/502657
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
For #57411.
Change-Id: I94982d939d16ad17174f801cc167cc10ddc8da30
Reviewed-on: https://go-review.googlesource.com/c/go/+/501696
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
The section on type inference has not been updated yet for Go 1.21.
Add a temporary note so that readers referred to this section from
the release notes are not confused.
Change-Id: Idc4c74d6d700f891c625289e873ad5aa9c2c5213
Reviewed-on: https://go-review.googlesource.com/c/go/+/501308
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Fixes#60570.
Change-Id: I7ef834731ea26ceee5ec9b7438fdd8323aaf828e
Reviewed-on: https://go-review.googlesource.com/c/go/+/500416
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
For #59488.
Change-Id: I50f65216bf02b42c1e0619702833f4a6dbed8925
Reviewed-on: https://go-review.googlesource.com/c/go/+/498136
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Put the sections for the various built-ins into alphabetical order
based on the built-in name, while keeping built-ins that belong
together together.
The order is now (captialized letter determines order):
- Append
- Clear
- Close
- Complex, real, imag
- Delete
- Len, cap
- Make
- Min, max (to be inserted here)
- New
- Panic, recover
- Print, println
There are some white space adjustments but no changes to the prose
of the moved sections.
Change-Id: Iaec509918c6bc965df3f28656374de03279bdc9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/498135
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
"placeholder" (no space) is already used in the spec and seems to be
the preferred option.
Removed space from "place holder".
Change-Id: I9b98f62f0e3f5adb019b99f5271cc9d19abf505e
GitHub-Last-Rev: ed5aaf9d02
GitHub-Pull-Request: golang/go#59626
Reviewed-on: https://go-review.googlesource.com/c/go/+/484576
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
In the language specification under "Constants" the lists matching default
types to untyped contstant types is missing an Oxford comma in the first
list. I found a number of other places in the spec and #23442 that use the
Oxford comma to support its use.
Add missing Oxford comma in Constants default type list.
Change-Id: I4562d692610334bc82452db076145d2414617a04
GitHub-Last-Rev: 8acdb60d6e
GitHub-Pull-Request: golang/go#59528
Reviewed-on: https://go-review.googlesource.com/c/go/+/483555
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Fixes#59506
Change-Id: I2f8b92e93b706b061ca0eb0bd52e5cf798ce9ede
Reviewed-on: https://go-review.googlesource.com/c/go/+/483358
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
The typechecker already enforces this semantic, but the spec is not
updated when unsafe.{SliceData,String,StringData} were added.
Change-Id: I4ee8c564d5681b2a5fd31ff424a31bdf065d9f3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/467756
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Change-Id: I5e3aca2b8fc78f38c9e2cdc67adf86d57ac85b1c
GitHub-Last-Rev: 0e5ddffe33
GitHub-Pull-Request: golang/go#58353
Reviewed-on: https://go-review.googlesource.com/c/go/+/465615
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Long ago we decided that panic(nil) was too unlikely to bother
making a special case for purposes of recover. Unfortunately,
it has turned out not to be a special case. There are many examples
of code in the Go ecosystem where an author has written panic(nil)
because they want to panic and don't care about the panic value.
Using panic(nil) in this case has the unfortunate behavior of
making recover behave as though the goroutine isn't panicking.
As a result, code like:
func f() {
defer func() {
if err := recover(); err != nil {
log.Fatalf("panicked! %v", err)
}
}()
call1()
call2()
}
looks like it guarantees that call2 has been run any time f returns,
but that turns out not to be strictly true. If call1 does panic(nil),
then f returns "successfully", having recovered the panic, but
without calling call2.
Instead you have to write something like:
func f() {
done := false
defer func() {
if err := recover(); !done {
log.Fatalf("panicked! %v", err)
}
}()
call1()
call2()
done = true
}
which defeats nearly the whole point of recover. No one does this,
with the result that almost all uses of recover are subtly broken.
One specific broken use along these lines is in net/http, which
recovers from panics in handlers and sends back an HTTP error.
Users discovered in the early days of Go that panic(nil) was a
convenient way to jump out of a handler up to the serving loop
without sending back an HTTP error. This was a bug, not a feature.
Go 1.8 added panic(http.ErrAbortHandler) as a better way to access the feature.
Any lingering code that uses panic(nil) to abort an HTTP handler
without a failure message should be changed to use http.ErrAbortHandler.
Programs that need the old, unintended behavior from net/http
or other packages can set GODEBUG=panicnil=1 to stop the run-time error.
Uses of recover that want to detect panic(nil) in new programs
can check for recover returning a value of type *runtime.PanicNilError.
Because the new GODEBUG is used inside the runtime, we can't
import internal/godebug, so there is some new machinery to
cross-connect those in this CL, to allow a mutable GODEBUG setting.
That won't be necessary if we add any other mutable GODEBUG settings
in the future. The CL also corrects the handling of defaulted GODEBUG
values in the runtime, for #56986.
Fixes#25448.
Change-Id: I2b39c7e83e4f7aa308777dabf2edae54773e03f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/461956
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
