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Daniel Martí 202e903144 text/template: recover panics during function calls
There's precedent in handling panics that happen in functions called
from the standard library. For example, if a fmt.Formatter
implementation fails, fmt will absorb the panic into the output text.

Recovering panics is useful, because otherwise one would have to wrap
some Template.Execute calls with a recover. For example, if there's a
chance that the callbacks may panic, or if part of the input data is nil
when it shouldn't be.

In particular, it's a common confusion amongst new Go developers that
one can call a method on a nil receiver. Expecting text/template to
error on such a call, they encounter a long and confusing panic if the
method expects the receiver to be non-nil.

To achieve this, introduce safeCall, which takes care of handling error
returns as well as recovering panics. Handling panics in the "call"
function isn't strictly necessary, as that func itself is run via
evalCall. However, this makes the code more consistent, and can allow
for better context in panics via the "call" function.

Finally, add some test cases with a mix of funcs, methods, and func
fields that panic.

Fixes #28242.

Change-Id: Id67be22cc9ebaedeb4b17fa84e677b4b6e09ec67
Reviewed-on: https://go-review.googlesource.com/c/143097
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
2018-10-24 09:09:21 +00:00
.github .github: use HTTPS for Stack Overflow link in SUPPORT.md 2018-06-12 11:08:14 +00:00
api syscall: FreeBSD 12 ino64 support 2018-10-05 21:38:13 +00:00
doc spec: refer to "run-time panic" rather than "exception" (cleanup) 2018-10-23 23:03:59 +00:00
lib/time lib/time: update vendored tzdata to release 2018e 2018-06-11 14:47:06 +00:00
misc internal/traceparser: provide parser that uses less space and parses segments of runtime trace files 2018-10-23 14:00:14 +00:00
src text/template: recover panics during function calls 2018-10-24 09:09:21 +00:00
test cmd/compile: use proved bounds to remove signed division fix-ups 2018-10-23 02:29:44 +00:00
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