The inferior used in the process launch test prints out its working
directory using the `getcwd` function, which is not allowed to return
symbolic links in the path components. When testing against the output
from `getcwd` we should resolve the full path to match the expected
output.

The source manager test sets a breakpoint on a main-copy.c file that is
copied into the build output directory. The source manager resolves this
path to its real location. When testing the output from the source cache
we need to resolve the expected path in the test to remove symlinks.

Change `lldbtest.expect` to require the regexes in `patterns` be found in order – when the
`ordered` parameter is true. This matches the behavior of `substrs`.

The `ordered` parameter is true by default, so this change also fixes tests by either
tweaking the patterns to work in order, or by setting `ordered=False`.

I have often wanted to test with `patterns` and also verify the order. This change
allows that.

Co-authored-by: Eisuke Kawashima <e-kwsm@users.noreply.github.com>

We got a bug report that this message is confusing. In this particular
case, the line zero was due to compiler tail merging (in optimized
code). The main issue was the "no source code" part: in this case it's
kind of incorrect because -- even though we can't really know that --
the address is arguably associated with *multiple* lines of source code.

I've tried to make the new wording more neutral, and added a wink
towards compiler optimizations. I left out the "compiler generated" part
of the message because I couldn't find a way to squeeze that in nicely.
I'm also not entirely sure what it was referring to -- if this was
(just) function prologue/epilogue, then maybe leaving it out is fine, as
we're not likely to stop there anyway (?)

I also left out the function name, because:
- for template functions it gets rather long
- it's already present in the message, potentially twice (once in the
"frame summary" line and once in the snippet of code we show for the
function declaration)

---------

Co-authored-by: Jonas Devlieghere <jonas@devlieghere.com>

When retrieving the location of the function declaration, we were
dropping the file component on the floor, which resulted in an amusingly
confusing situation were we displayed the file containing the
implementation of the function, but used the line number of the
declaration. This patch fixes that.

It required a small refactor Function::GetStartLineSourceLineInfo to
return a SupportFile (instead of just the file spec), which in turn
necessitated changes in a couple of other places as well.

In TestSourceManager, test_artificial_source_location will give the
process restart prompt if you run the test individually. The reason is
that we run the process twice: first using a convenience function to run
to a specific breakpoint and then again to check for a specific message
emitted when you hit the breakpoint. Instead of running twice and making
the test difficult to run individually, we can just check for the
specific messages using other commands.

This uses [teyit](https://pypi.org/project/teyit/) to modernize asserts,
as recommended by the [unittest release
notes](https://docs.python.org/3.12/whatsnew/3.12.html#id3).

For example, `assertTrue(a == b)` is replaced with `assertEqual(a, b)`.
This produces better error messages, e.g. `error: unexpectedly found 1
and 2 to be different` instead of `error: False`.

All Python files in the LLVM repository were reformatted with Black [1].
Files inside the LLDB subproject were reformatted in 2238dcc39358. This
patch updates a handful of tests that were added or modified since then
and weren't formatted with Black.

[1] https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style/68257

We recently saw an uptick in internal reports complaining that LLDB is
slow when sources on network file systems are inaccessible. I looked at
the SourceManger and its cache and I think there’s some room for
improvement in terms of reducing file system accesses:

 1. We always resolve the path.
 2. We always check the timestamp.
 3. We always recheck the file system for negative cache hits.

D153726 fixes (1) but (2) and (3) are necessary because of the cache’s
current design. Source files are cached at the debugger level which
means that the source file cache can span multiple targets and
processes. It wouldn't be correct to not reload a modified or new file
from disk.

We can however significantly reduce the number of file system accesses
by using a two level cache design: one cache at the debugger level and
one at the process level:

 - The cache at the debugger level works the way it does today. There is
   no negative cache: if we can't find the file on disk, we'll try again
   next time the cache is queried. If a cached file's timestamp changes
   or if its path remapping changes, the cached file is evicted and we
   reload it from disk.
 - The cache at the process level is design to avoid accessing the file
   system. It doesn't check the file's modification time. It caches
   negative results, so if a file didn't exist, it doesn't try to reread
   it from disk. Checking if the path remapping changed is cheap
   (doesn't involve checking the file system) and is the only way for a
   file to get evicted from the process cache.

The result of this patch is that LLDB will not show you new content if a
file is modified or created while a process is running. I would argue
that this is what most people would expect, but it is a change from how
LLDB behaves today.

For an average stop, we query the source cache 4 times. With the current
implementation, that's 4 stats to get the modification time, If the file
doesn't exist on disk, that's an additional 4 stats. Before D153726, if
the path starts with a ~ there are another additional 4 calls to
realpath. When debugging sources on a slow (network) file system, this
quickly adds up.

In addition to the two level caching, this patch also adds a source
logging channel and synchronization to the source file cache. The
logging was helpful during development and hopefully will help us triage
issues in the future. The synchronization isn't a new requirement: as
the cache is shared across targets, there is no guarantees that it can't
be accessed concurrently. The patch also fixes a bug where we would only
set the source remapping ID if the un-remapped file didn't exist, which
led to the file getting evicted from the cache on every access.

rdar://110787562

Differential revision: https://reviews.llvm.org/D153834

Add two new source subcommands: source cache dump and source cache
clear. As the name implies the first one dumps the source cache while
the later clears the cache.

This patch was motivated by a handful of (internal) bug reports related
to sources not being available. Right now those issues can be hard to
diagnose. The new commands give users, as well as us as developers, more
insight into and control over the source cache.

Differential revision: https://reviews.llvm.org/D153685