258 lines
7.8 KiB
Markdown
258 lines
7.8 KiB
Markdown
# NEO-GO smart contract compiler
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The neo-go compiler compiles Go programs to bytecode that the NEO virtual machine can understand.
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## Language compatibility
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The compiler is mostly compatible with regular Go language specification, but
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there are some important deviations that you need to be aware of that make it
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a dialect of Go rather than a complete port of the language:
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* `make()` ane `new()` are not supported, most of the time you can substitute
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them with composite literals
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* there is no real distinction between different integer types, all of them
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work as big.Int in Go with a limit of 256 bit in width, so you can use
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`int` for just about anything. This is the way integers work in Neo VM and
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adding proper Go types emulation is considered to be too costly.
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* goroutines, channels and garbage collection are not supported and will
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never be because emulating that aspects of Go runtime on top of Neo VM is
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close to impossible
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* even though `panic()` is supported, `recover()` is not, `panic` shuts the
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VM down
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* lambdas are not supported
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* global variables can't be changed in functions (#638)
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* it's not possible to rename imported interop packages, they won't work this
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way (#397, #913)
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* nested selectors are not yet supported (#957)
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* using value variable in range-based loops is not yet supported (#958)
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## VM API (interop layer)
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Compiler translates interop function calls into NEO VM syscalls or (for custom
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functions) into NEO VM instructions. [Refer to
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pkg.go.dev](https://pkg.go.dev/github.com/nspcc-dev/neo-go/pkg/interop)
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for full API documentation. In general it provides the same level of
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functionality as Neo .net Framework library.
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## Quick start
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### Compiling
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```
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./bin/neo-go contract compile -i mycontract.go
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```
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By default the filename will be the name of your .go file with the .avm extension, the file will be located in the same directory where your Go contract is. If you want another location for your compiled contract:
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```
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./bin/neo-go contract compile -i mycontract.go --out /Users/foo/bar/contract.avm
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```
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### Debugging
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You can dump the opcodes generated by the compiler with the following command:
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```
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./bin/neo-go contract inspect -i mycontract.go
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```
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This will result in something like this:
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```
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INDEX OPCODE DESC
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0 0x54 PUSH4
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1 0xc5 NEWARRAY
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2 0x6b TOALTSTACK
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3 0x1 PUSHBYTES1
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3 0x2a *
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5 0x6a DUPFROMALTSTACK
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6 0x0 PUSH0
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7 0x52 PUSH2
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8 0x7a ROLL
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9 0xc4 SETITEM
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10 0x6a DUPFROMALTSTACK
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11 0x0 PUSH0
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12 0xc3 PICKITEM
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13 0x5a PUSH10
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14 0xa2 GTE
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15 0x64 JMPIFNOT
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16 0x7 7
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16 0x0 0
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18 0x51 PUSH1
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19 0x6c FROMALTSTACK
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20 0x75 DROP
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21 0x66 RET
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22 0x0 PUSH0
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23 0x6c FROMALTSTACK
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24 0x75 DROP
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25 0x66 RET
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```
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#### Neo Smart Contract Debugger support
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It's possible to debug contracts written in Go using standard [Neo Smart
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Contract Debugger](https://github.com/neo-project/neo-debugger/) which is a
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part of [Neo Blockchain
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Toolkit](https://github.com/neo-project/neo-blockchain-toolkit/). To do that
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you need to generate debug information using `--debug` option, like this:
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```
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$ ./bin/neo-go contract compile -i contract.go -o contract.avm --debug contract.debug.json
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```
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This file can then be used by debugger and set up to work just like for any
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other supported language.
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### Deploying
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Deploying a contract to blockchain with neo-go requires a configuration file
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with contract's metadata in YAML format, like the following:
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```
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project:
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author: Jack Smith
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email: jack@example.com
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version: 1.0
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name: 'Smart contract'
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description: 'Even smarter than Jack himself'
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hasstorage: true
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hasdynamicinvocation: false
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ispayable: false
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returntype: ByteArray
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parameters: ['String', 'Array']
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```
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It's passed to the `deploy` command via `-c` option:
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```
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$ ./bin/neo-go contract deploy -i contract.avm -c contract.yml -e http://localhost:20331 -w wallet.json -g 0.001
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```
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Deployment works via an RPC server, an address of which is passed via `-e`
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option and should be signed using a wallet from `-w` option. More details can
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be found in `deploy` command help.
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#### Neo Express support
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It's possible to deploy contracts written in Go using [Neo
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Express](https://github.com/neo-project/neo-express) which is a part of [Neo
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Blockchain
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Toolkit](https://github.com/neo-project/neo-blockchain-toolkit/). To do that
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you need to generate a different metadata file using YAML written for
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deployment with neo-go. It's done in the same step with compilation via
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`--config` input parameter and `--abi` output parameter, combined with debug
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support the command line will look like this:
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```
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$ ./bin/neo-go contract compile -i contract.go --config contract.yml -o contract.avm --debug contract.debug.json --abi contract.abi.json
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```
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This file can then be used by toolkit to deploy contract the same way
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contracts in other languagues are deployed.
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### Invoking
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You can import your contract into the standalone VM and run it there (see [VM
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documentation](vm.md) for more info), but that only works for simple contracts
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that don't use blockchain a lot. For more real contracts you need to deploy
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them first and then do test invocations and regular invocations with `contract
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testinvokefunction` and `contract invokefunction` commands (or their variants,
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see `contract` command help for more details. They all work via RPC, so it's a
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mandatory parameter.
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Example call (contract `f84d6a337fbc3d3a201d41da99e86b479e7a2554` with method
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`balanceOf` and method's parameter `AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y` using
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given RPC server and wallet and paying 0.00001 GAS for this transaction):
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```
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$ ./bin/neo-go contract invokefunction -e http://localhost:20331 -w my_wallet.json -g 0.00001 f84d6a337fbc3d3a201d41da99e86b479e7a2554 balanceOf AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y
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```
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## Smart contract examples
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Some examples are provided in the [examples directory](../examples).
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### Check if the invoker of the contract is the owning address
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```Golang
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package mycontract
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import (
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"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
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"github.com/nspcc-dev/neo-go/pkg/interop/util"
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)
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var owner = util.FromAddress("AJX1jGfj3qPBbpAKjY527nPbnrnvSx9nCg")
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func Main() bool {
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isOwner := runtime.CheckWitness(owner)
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if isOwner {
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runtime.Log("invoker is the owner")
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return true
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}
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return false
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}
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```
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### Simple token
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```Golang
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package mytoken
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import (
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"github.com/nspcc-dev/neo-go/pkg/interop/runtime"
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"github.com/nspcc-dev/neo-go/pkg/interop/storage"
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)
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var owner = util.FromAddress("AJX1jGfj3qPBbpAKjY527nPbnrnvSx9nCg")
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type Token struct {
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Name string
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Symbol string
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TotalSupply int
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Owner []byte
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}
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func (t Token) AddToCirculation(amount int) bool {
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ctx := storage.Context()
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inCirc := storage.Get(ctx, "in_circ").(int)
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inCirc += amount
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storage.Put(ctx, "in_circ", inCirc)
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return true
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}
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func newToken() Token {
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return Token{
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Name: "your awesome NEO token",
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Symbol: "YANT",
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TotalSupply: 1000,
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Owner: owner,
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}
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}
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func Main(operation string, args []interface{}) bool {
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token := newToken()
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trigger := runtime.GetTrigger()
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if trigger == runtime.Verification() {
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isOwner := runtime.CheckWitness(token.Owner)
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if isOwner {
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return true
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}
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return false
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}
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if trigger == runtime.Application() {
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if operation == "mintTokens" {
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token.AddToCirculation(100)
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}
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}
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return true
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}
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```
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## How to report compiler bugs
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1. Make a proper testcase (example testcases can be found in the tests folder)
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2. Create an issue on Github
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3. Make a PR with a reference to the created issue, containing the testcase that proves the bug
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4. Either you fix the bug yourself or wait for patch that solves the problem
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