Fix error when raising a macro exception with empty message

[jan-zajic]

Unmasked stacktrace:

Unhandled exception: Index out of bounds (IndexError)
from src/array.cr:0:13 in 'shift'
from src/compiler/crystal/semantic/exception.cr:127:28 in 'append_to_s'
from src/compiler/crystal/semantic/exception.cr:95:7 in 'to_s_with_source'
from src/compiler/crystal/exception.cr:12:7 in 'to_s'
from src/io.cr:184:5 in '<<'
from src/io.cr:241:5 in 'puts'
from src/compiler/crystal/command.cr:115:7 in 'run'
from src/compiler/crystal/command.cr:46:5 in 'run'
from src/compiler/crystal/command.cr:45:3 in 'run'
from src/compiler/crystal.cr:8:1 in '__crystal_main'
from src/crystal/main.cr:97:5 in 'main_user_code'
from src/crystal/main.cr:86:7 in 'main'
from src/crystal/main.cr:106:3 in 'main'
from __libc_start_main
from _start
from ???

Fixes #8631

[bcardiff]

There are a couple of specs that stress there is some information in the backtrace (search for backtrace_sample).

I'm not familiar with the current error reporting code but I would like that some spec is added for this fix.

[jan-zajic]

But @bcardiff this fail only at compile time if you raise inside macro. If you raise "" outside of macro, it works just fine. Fix is in compiler/crystal/semantic/exception.cr. So i rather add spec to spec/compiler/semantic/macro_spec.cr, is it ok?

[bcardiff]

Sure @jan-zajic, that should work:

crystal/spec/compiler/semantic/macro_spec.cr

Lines 277 to 300 in 2dd66ab

	it "executes raise inside macro" do
	ex = assert_error %(
	macro foo
	{{ raise "OH NO" }}
	end
	foo
	), "OH NO"
	ex.to_s.should_not contain("expanding macro")
	end
	it "executes raise inside macro, with node (#5669)" do
	ex = assert_error %(
	macro foo(x)
	{{ x.raise "OH\nNO" }}
	end
	foo(1)
	), "OH"
	ex.to_s.should contain "NO"
	ex.to_s.should_not contain("expanding macro")
	end

But there needs to be more information about the backtrace. Even if the test becomes a bit fragile to maintain IMO

[straight-shoota]

But there needs to be more information about the backtrace.

That would be nice, but is not a requirement for merging this bugfix.