So that (*codegen).Visit is able to omit code generation for these
unused global vars. The most tricky part is to detect unused global
variables, it is done in several steps:
1. Collect the set of named used/unused global vars.
2. Collect the set of globally declared expressions that contain
function calls.
3. Pick up global vars from the set made at step 2.
4. Traverse used functions and puck up those global vars that are used
from these functions.
5. Rename all globals that are presented in the set made at step 1
but are not presented in the set made on step 3 or step 4.
Move all auxiliary function declaration after Main, so that INITSLOT
instructions counter works properly. `vmAndCompileInterop` loads program
and moves nextIP to the Main function offset if there's no _init
function. If _init is there, then nextIP will be moved to the start of
_init. In TestInline we don't handle instructions properly (CALL/JMP
don't change nextIP), we just perform instruction traversal from the
start point via Next(), thus INITSLOT counter value depends on the
starting instruction, which depends on _init presence.
If variable is unnamed and does not contain function call then it's
treated as unused and code generation may be omitted for it
initialization/declaration.
In case if global var is unnamed (and, as a consequence, unused) and
contains a function call inside its value specification, we need to emit
code for this var to be able to call the function as it can have
side-effects. See the example:
```
package foo
import "github.com/nspcc-dev/neo-go/pkg/interop/runtime"
var A = f()
func Main() int {
return 3
}
func f() int {
runtime.Notify("Valuable notification", 1)
return 2
}
```
Blockchain's notificationDispatcher sends events to channels and these
channels must be read from. Unfortunately, regular service shutdown procedure
does unsubscription first (outside of the read loop) and only then drains the
channel. While it waits for unsubscription request to be accepted
notificationDispatcher can try pushing more data into the same channel which
will lead to a deadlock. Reading in the same method solves this, any number of
events can be pushed until unsub channel accepts the data.
Unsubscribe and drain first, then return from the Shutdown method. It's
important wrt to subsequent chain shutdown process (normally it's closed right
after the network server).
Unfortunately Go doesn't allow to easily reuse readers in full packages, still
we can have this wrapper with a little overhead (the alternative is to move
specific methods into types of their own, but I'm not sure how it's going to
be accepted user-side).
Notice that int64 types are used for gas per block or registration price
because the price has to fit into the system fee limitation and gas per block
value can't be more than 10 GAS. We use int64 for votes as well in other types
since NEO is limited to 100M.
An attempt to compile the following code leads to runtime panic:
```
package foo
type CustomInt int
func Main() int {
var i CustomInt
i = 5
return i.Do(2)
}
func (CustomInt) Do(arg int) int {
return arg
}
```
The panic:
```
panic: runtime error: index out of range [0] with length 0 [recovered]
panic: runtime error: index out of range [0] with length 0
goroutine 22 [running]:
testing.tRunner.func1.2({0xa341c0, 0xc0001606d8})
/usr/local/go/src/testing/testing.go:1209 +0x24e
testing.tRunner.func1()
/usr/local/go/src/testing/testing.go:1212 +0x218
panic({0xa341c0, 0xc0001606d8})
/usr/local/go/src/runtime/panic.go:1038 +0x215
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).convertFuncDecl(0xc00015e3c0, {0xc753b8, 0xc000152c80}, 0xc000266300, 0x30)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/codegen.go:497 +0x10b3
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).compile.func2(0xc000152c80, 0xc00023c410)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/codegen.go:2153 +0x3f8
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).ForEachFile.func1(0xc000229b80)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/compiler.go:102 +0x82
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).ForEachPackage(0xc00015e3c0, 0xc000189bb0)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/compiler.go:93 +0xc6
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).ForEachFile(0x999a20, 0xc000130d80)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/compiler.go:99 +0x45
github.com/nspcc-dev/neo-go/pkg/compiler.(*codegen).compile(0xc00015e3c0, 0xc0002669f0, 0x1)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/codegen.go:2140 +0x445
github.com/nspcc-dev/neo-go/pkg/compiler.codeGen(0xc0002669f0)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/codegen.go:2191 +0x353
github.com/nspcc-dev/neo-go/pkg/compiler.CompileWithOptions({0xa6f39a, 0x50b6b3}, {0xc6d1a0, 0xc0002421e0}, 0x0)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/compiler.go:218 +0x65
github.com/nspcc-dev/neo-go/pkg/compiler_test.vmAndCompileInterop(0x5648df, {0xa9bf23, 0x94})
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/vm_test.go:75 +0x113
github.com/nspcc-dev/neo-go/pkg/compiler_test.eval(0xc0002421c0, {0xa9bf23, 0x61be8c7}, {0xa68880, 0xc0002421c0})
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/vm_test.go:36 +0x2d
github.com/nspcc-dev/neo-go/pkg/compiler_test.TestUnnamedMethodReceiver(0x4079f9)
/home/anna/Documents/GitProjects/nspcc-dev/neo-go/pkg/compiler/function_call_test.go:400 +0x4f
testing.tRunner(0xc000204b60, 0xbcebb0)
/usr/local/go/src/testing/testing.go:1259 +0x102
created by testing.(*T).Run
/usr/local/go/src/testing/testing.go:1306 +0x35a
```
The solution is to use the same approach as for unnamed function
parameters handling introduced in #2204. (c *funcScope).newVariable is
able to properly handle "_" receiver.
C# servers with SessionEnabled=false will return iterator IDs and no session
IDs which can be reported as an error immediately because the iterator can't
be traversed.
And test it with the RPC server.
Notice that getters still return int64 instead of *big.Int, that's because
these values are very limited and technically could even fit into an int (but
that seems to be too dangerous to use for long-term compatibility).
