tree c534b4d0d95c77648c4ab72f4d42af09952f9e87
parent c19225224b1344c932d4364c3d9f81085b65fe53
author Jens Johansen <jensj@google.com> 1607424463 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1607424463 +0000

[VM] Read and report constant constructor coverage from dill (2nd try)

This CL makes use of the now included constant constructor coverage
in the dill file.

It works like this:
* When the CFE evaluates constants, every constant constructor
  invocation evaluated saves the reference to the constructor in the
  `Source` (from the Components uri to source table) for the callers
  Library.
* This data is loaded into the VM in a "raw" format.
* When a request for coverage comes in, the VM - on top of the normal
  coverage processing - goes through all scripts to find constant
  constructor coverage for the requested script and offset. Note that
  all scripts must be checked because library A can have evaluated a
  constructor from library B - so even if only coverage for library B
  was requested, library A has to be checked.
  For all constructors found the start and end position is reported as
  covered. Note that this does not mark any initializes and there are
  (at least currently) no good way of marking which initializes were
  evaluated (because it has to be stable across edits even when the
  `advanced invalidation feature` is enabled).
* Note that the reason for the coverage to work on references - as
  hinted above - is because we want it to be stable across hot reloads
  even if/when advanced invalidation is enabled. This means, that
  library A cannot record "positional coverage" for library B because
  library B might get (for instance) new comments that will make any old
  offsets invalid. By using references we always lookup in the current
  world and use the correct offsets.

https://github.com/dart-lang/sdk/issues/38934

TEST=Existing test suite, new tests for the new coverage added.

Change-Id: I29531247a4b91a99d9a459cfdefbb9798e9c948f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175246
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>