Thank you to: @polinasok, @aurkenb, @pohzipohzi, @chainhelen,
@hitzhangjie, @eliben, @suzmue, @andreimatei, @aaronsky.

Fix some stale comments and add some comments that I would have found
useful.

This is needed to fix the problem we have with 1.15.4+ after the
backport is applied to it. The DWARF standard isn't clear on what
should happen with the end_of_sequence opcode but this is consistent
with debug/dwarf.LineReader as well as gdb.

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

* service/dap: expand goroutine info in threads response

* Fix checks

* Make DeepSource happy
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

* Use the active xcode-select path instead of a hardcoded Xcode path

* Refactored exec.Command to invoke Output instead of running with a custom buffer for stdout

Addresses review comment by @derekparker

Change FindLocation to apply substitute path rules to location
expressions. Changes terminal to always print paths after applying
substitutions.

Implements #2203

1. Forward stdin/stdout/stderr to the target process when in foreground
   mode instead of always forwarding the current tty (issue #1964)
2. When redirecting a file descriptor make sure to also specify
   something for all three otherwise debugserver will misbehave (either
   exit on launch or run but giving the target process a closed file
   descriptor).

Fixes #1964

See https://github.com/golang/go/issues/42484

This patch adds some comments around RequestManualStop().

* Support evaluate request

* Fix failing tests

* Call support

* Remove debugger.CurrentThread() that got accidentally reintroduced during merge

* Address review comments

* Function to stringify stop reason

* Add resetHandlesForStop

* Handle stop inside call

* More tests

* Address review comments

* Check all threads to determine if call completed

* Fix test

* Fix test

* Fix test

* Address review comments
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

On linux we can not read memory if the thread we use to do it is
occupied doing certain system calls. The exact conditions when this
happens have never been clear.

This problem was worked around by using the Blocked method which
recognized the most common circumstances where this would happen.

However this is a hack: Blocked returning true doesn't mean that the
problem will manifest and Blocked returning false doesn't necessarily
mean the problem will not manifest. A side effect of this is issue
#2151 where sometimes we can't read the memory of a thread and find its
associated goroutine.

This commit fixes this problem by always reading memory using a thread
we know to be good for this, specifically the one returned by
ContinueOnce. In particular the changes are as follows:

1. Remove (ProcessInternal).CurrentThread and
(ProcessInternal).SetCurrentThread, the "current thread" becomes a
field of Target, CurrentThread becomes a (*Target) method and
(*Target).SwitchThread basically just sets a field Target.

2. The backends keep track of their own internal idea of what the
current thread is, to use it to read memory, this is the thread they
return from ContinueOnce as trapthread

3. The current thread in the backend and the current thread in Target
only ever get synchronized in two places: when the backend creates a
Target object the currentThread field of Target is initialized with the
backend's current thread and when (*Target).Restart gets called (when a
recording is rewound the currentThread used by Target might not exist
anymore).

4. We remove the MemoryReadWriter interface embedded in Thread and
instead add a Memory method to Process that returns a MemoryReadWriter.
The  backends will return something here that will read memory using
the current thread saved by the backend.

5. The Thread.Blocked method is removed

One possible problem with this change is processes that have threads
with different memory maps. As far as I can determine this could happen
on old versions of linux but this option was removed in linux 2.5.

Fixes #2151

TestStepConcurrentDirect will occasionally fail (7% of the time on my
setup) by either causing the target processs to execute an invalid
instruction or (more infrequently) by switching to the wrong thread.

Both of those are caused by receiving SIGTRAPs for threads hitting a
breakpoint after it has been removed (the thread hits the breakpoint,
we stop everything and remove the breakpoint and only after we receive
the signal).

Change native.(*nativeProcess).stop to handle SIGTRAPs that can't be
attributed to a breakpoint, a hardcoded breakpoint in the program's
text, or manual stops (and therefore are likely caused by phantom
breakpoint hits).
Co-authored-by: Na <a@kra>

Fixes #2219

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

* service/rpccommon: log error for conns rejected by --only-same-user

If no logger is enabled manually write to stderr instead.

Fixes #2209

* logflags: fix style complaints from DeepSource

Fixes #1847

1. Remove bug about unsupport systems, because we has pretty error msg.
2. Add usage for remote debugging.

Relate: #1883, #1829, #861, #1332.

The test needs to set a breakpoint on main.CallFn after the prologue,
on linux/386 this function does not have any instruction after the
prologue on the function header line  because it doesn't need to
allocate space for local variables. Change the fixture so that this
isn't a problem.

This bug results on the test failing a small percentage of the time.
Co-authored-by: Na <a@kra>

It returns an unexported type and is only used in a single place.

Due to a missing check TestCgoStacktrace2 didn't actually check
anything. Enable it and then skip it on linux/386 and linux/arm64 where
it's broken.
Co-authored-by: Na <a@kra>

If the process receives a signal (or sends a singal to itself) and then
dies before we can route the signal back to it we still need to
retrieve its exit status.

Fixes a rare failure of TestIssue1101 in proc_test.go
Co-authored-by: Na <a@kra>

* service/dap: add "panic" and "fatal error" as stopped reasons

The unrecovered panic and fatal throw breakpoints are not set by the
user. We now check for these special breakpoints and send appropriate
stopped reasons to the client.

* Add getter for StopReason

* Set threadID and stop reason correctly

If there is no selected goroutine, no goroutine ID should be set in
the stopped event.

The stopped reason can be better determined using the process
StopReason.

* Update panic breakpoint on next test to work with Go 1.13 runtime

When running panic.go with Go1.13, the next line that is stepped to
after panic('boom') is the defer function in the runtime package. The
unrecovered panic breakpoint is not hit until after several steps.

The test now steps until the breakpoint is hit, or the program terminates
without hitting the unrecovered panic breakpoint, in which case it fails.

* Skip breakpoint on next test in < Go 1.14

* Support clearing breakpoints and setting conditions

* Return unverified breakpoints with errors
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

* Add underlying type when printing interface type

* Add todo to remove one level from interface printing
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

* proc/tests: keep track of tests skipped due to backend problems

Mark tests skipped due to backend problems and add a script to keep
track of them.

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.

* proc: use argument position for addr only when injecting function calls

We can not, in general, use the argument position to determine the
address of a formal parameter, it will not work in presence of
optimizations or inlining. In those cases formal arguments could be
stored in registers.

Fixes #2176

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.
Co-authored-by: Na <a@kra>

* dwarf/line: ignore end_of_sequence entry if AllPCsBetween

Go 1.15 (but possibly prior versions of Go too) has a tendency to use
an address in the middle of an instruction for this entry, but if it
was correct it would be after the last instruction of the function
anyway.

This problem manifests especially frequently as a target crash in
TestStepConcurrentPtr on linux/arm64 (~6% of the runs).

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.
Co-authored-by: Na <a@kra>

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.

* service/*: remove threadID argument of (*Debugger).PackageVariables

Which thread is used doesn't make any difference to the list of package
variables that is returned and this option was only ever used by an old
v1 API call.

* Revert "proc: Find executable should follow symbol links."

This reverts commit 3e04ad0f.

* proc: resolve symlinks when searching for split debug_info if path is /proc/pid/exe

Fixes #2168

Pulls in v0.3.0 of google/go-dap; this version has some fixes and API
improvements which service/dap will be able to leverage to clean up some
code.

During the testing of the core dump generation feature two bugs were
discovered in gdbserial:

1. we don't check that both bytes of the checksum are read, if the
   buffer only has one byte we can end up reading only one byte instead
   of two and the second byte will mess up the parsing of the next
   packet
2. binary encoded packets can start with an 'E' and not be errors, when
   using binary responses add an extra check for the lenght of the
   response before deciding that the response is an error.
   Unfortunately this encoding is inherently ambiguous (we can't
   distinguish a 3 byte response starting with 'E' from an error) so
   binary requests that lead to short responses should be avoided.

Testing this is complicated, they will be tested implicitly by the
upcoming core dump test.
Co-authored-by: Na <a@kra>

* Support global variables

* Respond to review comments

* Clarify comment

* Add more details to test error messages

* Remove flaky main..inittask checks

* Rename globals flag to match vscode-go

* Normalize filepath with slash separator

* Improve handling for unknown package

* Tweak error message

* More refactoring, normalization and error details to deal with Win test failures

* Clean up optional launch args processing

* Add CurrentPackage to debugger and use instead of ListPackagesBuildInfo
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

Adds a -size argument to examinemem that specifies how to group bytes on output.