eth/tracers, core: use scopecontext in tracers, provide statedb in capturestart (#22333)

Fixes the CaptureStart api to include the EVM, thus being able to set the statedb early on. This pr also exposes the struct we used internally in the interpreter to encapsulate the contract, mem, stack, rstack, so we pass it as a single struct to the tracer, and removes the error returns on the capture methods.

eth/tracers/tracer_test.go

@@ -47,7 +47,8 @@ type dummyStatedb struct {
 	state.StateDB
 }
 
-func (*dummyStatedb) GetRefund() uint64 { return 1337 }
+func (*dummyStatedb) GetRefund() uint64                       { return 1337 }
+func (*dummyStatedb) GetBalance(addr common.Address) *big.Int { return new(big.Int) }
 
 type vmContext struct {
 	blockCtx vm.BlockContext
@@ -67,7 +68,7 @@ func runTrace(tracer *Tracer, vmctx *vmContext) (json.RawMessage, error) {
 	contract := vm.NewContract(account{}, account{}, value, startGas)
 	contract.Code = []byte{byte(vm.PUSH1), 0x1, byte(vm.PUSH1), 0x1, 0x0}
 
-	tracer.CaptureStart(contract.Caller(), contract.Address(), false, []byte{}, startGas, value)
+	tracer.CaptureStart(env, contract.Caller(), contract.Address(), false, []byte{}, startGas, value)
 	ret, err := env.Interpreter().Run(contract, []byte{}, false)
 	tracer.CaptureEnd(ret, startGas-contract.Gas, 1, err)
 	if err != nil {
@@ -150,14 +151,55 @@ func TestHaltBetweenSteps(t *testing.T) {
 		t.Fatal(err)
 	}
 	env := vm.NewEVM(vm.BlockContext{BlockNumber: big.NewInt(1)}, vm.TxContext{}, &dummyStatedb{}, params.TestChainConfig, vm.Config{Debug: true, Tracer: tracer})
-	contract := vm.NewContract(&account{}, &account{}, big.NewInt(0), 0)
+	scope := &vm.ScopeContext{
+		Contract: vm.NewContract(&account{}, &account{}, big.NewInt(0), 0),
+	}
 
-	tracer.CaptureState(env, 0, 0, 0, 0, nil, nil, nil, contract, 0, nil)
+	tracer.CaptureState(env, 0, 0, 0, 0, scope, nil, 0, nil)
 	timeout := errors.New("stahp")
 	tracer.Stop(timeout)
-	tracer.CaptureState(env, 0, 0, 0, 0, nil, nil, nil, contract, 0, nil)
+	tracer.CaptureState(env, 0, 0, 0, 0, scope, nil, 0, nil)
 
 	if _, err := tracer.GetResult(); err.Error() != timeout.Error() {
 		t.Errorf("Expected timeout error, got %v", err)
 	}
 }
+
+// TestNoStepExec tests a regular value transfer (no exec), and accessing the statedb
+// in 'result'
+func TestNoStepExec(t *testing.T) {
+	runEmptyTrace := func(tracer *Tracer, vmctx *vmContext) (json.RawMessage, error) {
+		env := vm.NewEVM(vmctx.blockCtx, vmctx.txCtx, &dummyStatedb{}, params.TestChainConfig, vm.Config{Debug: true, Tracer: tracer})
+		startGas := uint64(10000)
+		contract := vm.NewContract(account{}, account{}, big.NewInt(0), startGas)
+		tracer.CaptureStart(env, contract.Caller(), contract.Address(), false, []byte{}, startGas, big.NewInt(0))
+		tracer.CaptureEnd(nil, startGas-contract.Gas, 1, nil)
+		return tracer.GetResult()
+	}
+	execTracer := func(code string) []byte {
+		t.Helper()
+		ctx := &vmContext{blockCtx: vm.BlockContext{BlockNumber: big.NewInt(1)}, txCtx: vm.TxContext{GasPrice: big.NewInt(100000)}}
+		tracer, err := New(code, ctx.txCtx)
+		if err != nil {
+			t.Fatal(err)
+		}
+		ret, err := runEmptyTrace(tracer, ctx)
+		if err != nil {
+			t.Fatal(err)
+		}
+		return ret
+	}
+	for i, tt := range []struct {
+		code string
+		want string
+	}{
+		{ // tests that we don't panic on accessing the db methods
+			code: "{depths: [], step: function() {}, fault: function() {},  result: function(ctx, db){ return db.getBalance(ctx.to)} }",
+			want: `"0"`,
+		},
+	} {
+		if have := execTracer(tt.code); tt.want != string(have) {
+			t.Errorf("testcase %d: expected return value to be %s got %s\n\tcode: %v", i, tt.want, string(have), tt.code)
+		}
+	}
+}