commit f296dad962e452ced1e5396b9ced7203747f7209
author littledan <littledan@chromium.org> Fri Sep 23 22:23:50 2016
committer Commit bot <commit-bot@chromium.org> Fri Sep 23 22:24:03 2016
tree 5b3425f2feb6bdc687088677336fdfe38f22defd
parent 72b01e4a41e3df784fce161a1928d9a7a3021aba

Improve stack traces for async functions

This patch tracks the stack of async functions differently from other
Promise async stack tracking. With this patch, the stack trace of a
callstack of async functions should look similarly to the call stack
if all of the functions were synchronous. An example can be found in
the updated test expectations: https://codereview.chromium.org/2362923002 .

The new stack traces are implemented using existing mechanisms in the
inspector. The inspector has two ways to save async stack traces: recurring
and non-recurring stacks. An example of a non-recurring stack is setTimeout,
and a recurring one is saved for setInterval. Recurring stacks are deleted
only when a special "cancel" function is called, rather than being deleted
after being used the first time. Previous Promise async stack tracking always
used non-recurring stacks.

For async functions, this patch saves a recurring stack. The top frame of
the stack is duplicated, as the resuming function contains a similar frame;
the devtools frontend is responsible for removing or marking this frame,
which it can do based on seeing the [async function] line which follows it.
The second frame will instead be provided by the resuming execution
context. The recurring stack is saved when the async function is entered, and
it is deleted from a finally block. The id of the stack is saved in the outer
Promise being constructed by the async function. When an intermediate
throwaway Promise will be triggered as a reaction, it will be identified as
such based on its debugging metadata, and the corresponding async function's
recurring stack will be used.

BUG=v8:4483

Review-Url: https://codereview.chromium.org/2357423002
Cr-Commit-Position: refs/heads/master@{#39695}