Change how cached diagnostics are stored inside the CAS. It used to be
stored as a standalone entry for a frontend invocation in the cache and
now it is switched to be associated with input files, stored together
with other outputs like object files, etc.
This enables cleaner Cache Replay APIs and future cached diagnostics
that can be splitted up by file contribution.
Update swift cache key computation mechanism from one cache key per
output, to one cache key per primary input file (for all outputs that
associated with that input).
The new schema allows fewer cache lookups while still preserving most of
the flexibility for batch mode and incremental mode.
In C++20, the compiler will synthesize a version of the operator
with its arguments reversed to ease commutativity. This reversed
version is ambiguous with the hand-written operator when the
argument is const but `this` isn't.
Teach CachedDiagnosticsProcessor to replay diagnostics for all consumers
with a different path using a path prefix map. This allows diagnostics
to be replayed for the actual path on disk after the scanner
canonicalized the path for compilation.
Rename `-enable-cas` to `-compile-cache-job` to align with clang option
names and promote that to a new driver only flag.
Few other additions to driver flag for caching behaviors:
* `-compile-cache-remarks`: now cache hit/miss remarks are guarded behind
this flag
* `-compile-cache-skip`: skip replaying from the cache. Useful as a
debugging tool to do the compilation using CAS inputs even the output
is a hit from the cache.
When using a FileSpecificDiagConsumer, the source file that doesn't have
any diagnostics need to exist in the source manager for the consumer to
be successfully created.
Add a CachedDiagnosticsProcessor that is a DiagConsumer can capture all
the diagnostics during a compilation, serialized them into CAS with a
format that can be replayed without re-compiling.
