This O(N^2) was introduced in 8b2c94c4.
Make it O(N).

Followup to 8b2c94c4

Allow matching sequences of marks attached to different ligatures,
as supposedly the base of the subsequent marks were already jumped
over.

If two marks want to ligate and they belong to different components of the
same ligature glyph, and said ligature glyph is to be ignored according to
mark-filtering rules, then allow.

Example Burmese senquence:

  U+1004,U+103A,U+1039,U+101B,U+103D,U+102D

Test font provided by Norbert Lindenberg.

Fixes https://github.com/behdad/harfbuzz/issues/545

Not all shapers code is updated to set this properly.
GSUB and Arabic shaper are updated.
GPOS and other shapers are NOT.

Fixes https://github.com/behdad/harfbuzz/issues/224

Not used yet.

Hide them like Mongolian Free Variation Selectors instead.

Fixes https://github.com/behdad/harfbuzz/issues/463

clang's new -Wcomma compiler option warns about possible misuse of the
comma operator such as between two statements.

hb-common.cc:190:9 [-Wcomma] possible misuse of comma operator here
hb-ot-layout-gsubgpos-private.hh:345:30 [-Wcomma] possible misuse of
comma operator here
hb-shape-plan.cc:438:26 [-Wcomma] possible misuse of comma operator here

This reverts commit b9b005f3.

This introduced invalid access cases. Revert until I fix correctly.

This was broken forever, since days that we did not allow moving
tape backwards. Works now. Reported by Doug Felt.

* Guard against underflow when adjusting length

With the fuzz-testcase in mozilla bug 1295299, we end up with a recursed lookup that removes 3 items, when `match_positions[idx]` is 0, which results in (unsigned) `end` wrapping to a huge value.

Making `end` a signed int is probably the simplest route to a fix.

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1295299.

* Add testcase for #421.

As discovered by libFuzzer / Chromium fuzzing.

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=659496
CC https://github.com/behdad/harfbuzz/issues/139

Yay!!!!

Not hooked up to shaper yet.

Untested.

Fixes https://github.com/behdad/harfbuzz/issues/253

Hopefully we got the logic right.

Fixes https://github.com/behdad/harfbuzz/issues/234

Fixes https://github.com/behdad/harfbuzz/issues/223

Right now we cannot test this because it has to be tested using hb-fuzzer.
We should move all fuzzing tests from test/shaping/tests/fuzzed.tests to
test/fuzzing/ and have its own test runner.  At that point, should add
test from this issue as well.

Say, if we are ligating "A B_C m D", then previously 'm' was being
attached to 'B' in the combined A_B_C_D ligature.  Now we attach it
to 'C'.  No test for this though :(.

We use three bits for lig_id these days, so we finally got a report of
two separate ligatures with the same lig_id happening adjacent to each
other, and then the component-handling code was breaking things.
Protect against that by ignoring same-lig-id but lig-comp=0 glyphs after
a new ligature.

Fixes https://github.com/behdad/harfbuzz/issues/198

This is just to make it harder to be extremely slow.  There definitely
are ways still, just harder.  Oh well... how do we tame this problem
without solving halting problem?!

Fixes https://github.com/behdad/harfbuzz/issues/174

If buf->idx is at end, don't set end past it...

Fixes https://github.com/behdad/harfbuzz/issues/173

Fixes assert fail in https://github.com/behdad/harfbuzz/issues/161
with libharfbuzz-fuzzing.

...at compile time.

https://bugzilla.mozilla.org/show_bug.cgi?id=1215894

This is a fix on top of the previous issue fixed in
c917965b.

This was caught by "libFuzzer" testing.

Not functional change (expected!).

Fixes possible invalid read of two bytes.

Reported by Behzad Najjarpour Jabbari, Secunia Research.