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log/slog: don't panic on aliased Record 

If the shared slice in a copied is modified, make a copy of it
and insert an attribute that warns of the bug.

Previously, we panicked, and panics in logging code should be avoided.

Change-Id: I24e9b0bf5c8cd09cf733e7dae8a82d025ef214e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/513760
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Jonathan Amsterdam 2023-07-28 10:35:10 -04:00
parent 8a6acecfab
commit cf39736f87
2 changed files with 10 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/log/slog/record.go
View File

@ -109,7 +109,9 @@ func (r *Record) AddAttrs(attrs ...Attr) {
if cap(r.back) > len(r.back) {
end := r.back[:len(r.back)+1][len(r.back)]
if !end.isEmpty() {
panic("copies of a slog.Record were both modified")
// Don't panic; copy and muddle through.
r.back = slices.Clip(r.back)
r.back = append(r.back, String("!BUG", "AddAttrs unsafely called on copy of Record made without using Record.Clone"))
}
}
ne := countEmptyGroups(attrs[i:])

11
src/log/slog/record_test.go
View File

@ -96,12 +96,15 @@ func TestAliasingAndClone(t *testing.T) {
r1.back = b
// Make a copy that shares state.
r2 := r1
// Adding to both should panic.
// Adding to both should insert a special Attr in the second.
r1AttrsBefore := attrsSlice(r1)
r1.AddAttrs(Int("p", 0))
if !panics(func() { r2.AddAttrs(Int("p", 1)) }) {
t.Error("expected panic")
}
r2.AddAttrs(Int("p", 1))
check(r1, append(slices.Clip(r1AttrsBefore), Int("p", 0)))
r1Attrs := attrsSlice(r1)
check(r2, append(slices.Clip(r1AttrsBefore),
String("!BUG", "AddAttrs unsafely called on copy of Record made without using Record.Clone"), Int("p", 1)))
// Adding to a clone is fine.
r2 = r1.Clone()
check(r2, r1Attrs)