This commit fixes two issues:
* Do not try to create the cached GOROOT multiple times in parallel.
This may happen in tests and is a waste of resources (and thus
speed).
* Check for an "access denied" error when trying to rename a directory
over an existing directory. On *nix systems, this results in the
expected "file exists" error. Unfortunately, Windows gives an access
denied. This commit fixes the Windows behavior.
... instead of generating one with math/rand. The problem was that
math/rand is deterministic across runs, resulting in a possible race
when trying to create the same directory between two processes.
Additionally, because I used `os.MkdirAll`, no error was reported when
the directory already existed. The solution to this is to use the stdlib
function designed for this: ioutil.TempDir.
Currently there will be a problem if the TinyGo installation directory
is not the same filesystem as the cache directory (usually the C drive)
and Developer Mode is disabled. Therefore, let's add another fallback
for when both conditions are true, falling back to copying the file
instead of symlinking/hardlinking it.
This commit changes the way that packages are looked up. Instead of
working around the loader package by modifying the GOROOT variable for
specific packages, create a new GOROOT using symlinks. This GOROOT is
cached for the specified configuration (Go version, underlying GOROOT
path, TinyGo path, whether to override the syscall package).
This will also enable go module support in the future.
Windows is a bit harder to support, because it only allows the creation
of symlinks when developer mode is enabled. This is worked around by
using symlinks and if that fails, using directory junctions or hardlinks
instead. This should work in the vast majority of cases. The only case
it doesn't work, is if developer mode is disabled and TinyGo, the Go
toolchain, and the cache directory are not all on the same filesystem.
If this is a problem, it is still possible to improve the code by using
file copies instead.
As a side effect, this also makes diagnostics use a relative file path
only when the file is not in GOROOT or in TINYGOROOT.
