docs: update compiler.md, bring it up to date

And add one more reference to it into the main README.

README.md

@@ -110,7 +110,9 @@ mode, after it ends the node can be started normally.
 Please refer to [neo-go smart contract development
 workshop](https://github.com/nspcc-dev/neo-go-sc-wrkshp) that shows some
 simple contracts that can be compiled/deployed/run using neo-go compiler, SDK
-and private network.
+and private network. For details on how Go code is translated to Neo VM
+bytecode and what you can and can not do in smart contract please refer to the
+[compiler documentation](docs/compiler.md).
 
 # Developer notes
 Nodes have such features as [Prometheus](https://prometheus.io/docs/guides/go-application) and 

docs/compiler.md

@@ -2,66 +2,39 @@
 
 The neo-go compiler compiles Go programs to bytecode that the NEO virtual machine can understand.
 
-## Currently supported
+## Language compatibility
 
-### Go internals 
-- type checking
-- multiple assignments
-- global variables
-- types int, string, byte and booleans
-- struct types + method receives
-- functions
-- composite literals `[]int, []string, []byte`
-- basic if statements
-- binary expressions
-- return statements
-- for loops
-- imports 
+The compiler is mostly compatible with regular Go language specification, but
+there are some important deviations that you need to be aware of that make it
+a dialect of Go rather than a complete port of the language:
+ * `make()` ane `new()` are not supported, most of the time you can substitute
+   them with composite literals
+ * there is no real distinction between different integer types, all of them
+   work as big.Int in Go with a limit of 256 bit in width, so you can use
+   `int` for just about anything. This is the way integers work in Neo VM and
+   adding proper Go types emulation is considered to be too costly.
+ * goroutines, channels and garbage collection are not supported and will
+   never be because emulating that aspects of Go runtime on top of Neo VM is
+   close to impossible
+ * even though `panic()` is supported, `recover()` is not, `panic` shuts the
+   VM down
+ * lambdas are not supported
+ * global variables can't be changed in functions (#638)
+ * it's not possible to rename imported interop packages, they won't work this
+   way (#397, #913)
+ * nested selectors are not yet supported (#957)
+ * using value variable in range-based loops is not yet supported (#958)
 
-### Go builtins
-- len
-- append
-
-### VM API (interop layer)
+## VM API (interop layer)
 Compiler translates interop function calls into NEO VM syscalls or (for custom
-functions) into NEO VM instructions. [Refer to GoDoc](https://godoc.org/github.com/nspcc-dev/neo-go/pkg/interop) for full API documentation.
-
-#### Standard NEO Smart Contract API
-- account
-- asset
-- attribute
-- block
-- blockchain
-- contract
-- engine
-- header
-- input
-- iterator
-- output
-- runtime
-- storage
-- transaction
-
-#### Custom VM utility helper functions
-- crypto:
-  - `SHA1`
-  - `SHA256`
-  - `Hash256`
-  - `Hash160`
-- enumerator
-- util:
-  - `Equals` (to emit `EQUALS` opcode, not needed usually)
-  - `FromAddress(address string) []byte`
-
-## Not supported
-Due to the limitations of the NEO virtual machine, features listed below will not be supported.
-- channels 
-- goroutines
-- returning multiple values from functions
+functions) into NEO VM instructions. [Refer to
+pkg.go.dev](https://pkg.go.dev/github.com/nspcc-dev/neo-go/pkg/interop)
+for full API documentation. In general it provides the same level of
+functionality as Neo .net Framework library.
 
 ## Quick start
 
-### Compile a smart contract
+### Compiling
 
 ```
 ./bin/neo-go contract compile -i mycontract.go
@@ -73,7 +46,7 @@ By default the filename will be the name of your .go file with the .avm extensio
 ./bin/neo-go contract compile -i mycontract.go --out /Users/foo/bar/contract.avm
 ```
 
-### Debugging your smart contract
+### Debugging
 You can dump the opcodes generated by the compiler with the following command:
 
 ```
@@ -112,33 +85,89 @@ INDEX    OPCODE    DESC
 25       0x66      RET
 ```
 
-### Test invoke a compiled contract
-You can simulate a test invocation of your compiled contract by the VM, to know the total gas cost for example, with the following command:
+#### Neo Smart Contract Debugger support
+
+It's possible to debug contracts written in Go using standard [Neo Smart
+Contract Debugger](https://github.com/neo-project/neo-debugger/) which is a
+part of [Neo Blockchain
+Toolkit](https://github.com/neo-project/neo-blockchain-toolkit/). To do that
+you need to generate debug information using `--debug` option, like this:
 
 ```
-./bin/neo-go contract testinvoke -i mycompiledcontract.avm
+$ ./bin/neo-go contract compile -i contract.go -o contract.avm --debug contract.debug.json
 ```
 
-Will output something like:
-```
-{
-  "state": "HALT, BREAK",
-  "gas_consumed": "0.006",
-  "Stack": [
-    {
-      "type": "Integer",
-      "value": "9"
-    }
-  ]
-}
+This file can then be used by debugger and set up to work just like for any
+other supported language.
+
+### Deploying
+
+Deploying a contract to blockchain with neo-go requires a configuration file
+with contract's metadata in YAML format, like the following:
 
 ```
+project:
+  author: Jack Smith
+  email: jack@example.com
+  version: 1.0
+  name: 'Smart contract'
+  description: 'Even smarter than Jack himself'
+  hasstorage: true
+  hasdynamicinvocation: false
+  ispayable: false
+  returntype: ByteArray
+  parameters: ['String', 'Array']
+```
 
-At the moment this is implemented via RPC call to the remote server.
+It's passed to the `deploy` command via `-c` option:
+
+```
+$ ./bin/neo-go contract deploy -i contract.avm -c contract.yml -e http://localhost:20331 -w wallet.json -g 0.001
+```
+
+Deployment works via an RPC server, an address of which is passed via `-e`
+option and should be signed using a wallet from `-w` option. More details can
+be found in `deploy` command help.
+
+#### Neo Express support
+
+It's possible to deploy contracts written in Go using [Neo
+Express](https://github.com/neo-project/neo-express) which is a part of [Neo
+Blockchain
+Toolkit](https://github.com/neo-project/neo-blockchain-toolkit/). To do that
+you need to generate a different metadata file using YAML written for
+deployment with neo-go. It's done in the same step with compilation via
+`--config` input parameter and `--abi` output parameter, combined with debug
+support the command line will look like this:
+
+```
+$ ./bin/neo-go contract compile -i contract.go --config contract.yml -o contract.avm --debug contract.debug.json --abi contract.abi.json 
+```
+
+This file can then be used by toolkit to deploy contract the same way
+contracts in other languagues are deployed.
+
+
+### Invoking
+You can import your contract into the standalone VM and run it there (see [VM
+documentation](vm.md) for more info), but that only works for simple contracts
+that don't use blockchain a lot. For more real contracts you need to deploy
+them first and then do test invocations and regular invocations with `contract
+testinvokefunction` and `contract invokefunction` commands (or their variants,
+see `contract` command help for more details. They all work via RPC, so it's a
+mandatory parameter.
+
+Example call (contract `f84d6a337fbc3d3a201d41da99e86b479e7a2554` with method
+`balanceOf` and method's parameter `AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y` using
+given RPC server and wallet and paying 0.00001 GAS for this transaction):
+
+```
+$ ./bin/neo-go contract invokefunction -e http://localhost:20331 -w my_wallet.json -g 0.00001 f84d6a337fbc3d3a201d41da99e86b479e7a2554 balanceOf AK2nJJpJr6o664CWJKi1QRXjqeic2zRp8y
+```
 
 ## Smart contract examples
 
-Some examples are provided in the [examples directory](examples).
+Some examples are provided in the [examples directory](../examples).
 
 ### Check if the invoker of the contract is the owning address