debug: incorrect expression for loading map children results in evaluation error

[polinasok]

Code:

nestedmap := map[string]interface{}{
		"issuer": map[string]interface{}{
			"foo1": map[string]interface{}{
				"foo2": "bar2",
			},
		},
	}
runtime.Breakpoint()

Launch configuration:

           "trace":"verbose",
           "dlvLoadConfig": {
                "followPointers": true,
                "maxVariableRecurse": 0, // <=================== change from default 1
                "maxStringLen": 64,
                "maxArrayValues": 64,
                "maxStructFields": -1
            }

At breakpoint, expand nestedmap in VARIABLES pane.
Logging output:

From client: variables({"variablesReference":1000})
To client: {"seq":0,"type":"response","request_seq":12,"command":"variables","success":true,"body":{"variables":[{"name":"nestedmap","value":"<map[string]interface {}> (length: 1)","evaluateName":"nestedmap","variablesReference":1001}]}}
VariablesResponse [
 {
  "name": "nestedmap",
  "value": "<map[string]interface {}> (length: 1)",
  "evaluateName": "nestedmap",
  "variablesReference": 1001
 }
]
// Expanding "nestedmap" triggers another variables request
From client: variables({"variablesReference":1001})
Failed to eval expression:  {
 "Expr": "nestedmap.nestedmap[\"issuer\"]",
 "Scope": {
  "goroutineID": -1,
  "frame": 0
 },
 "Cfg": {
  "followPointers": true,
  "maxVariableRecurse": 0,
  "maxStringLen": 64,
  "maxArrayValues": 64,
  "maxStructFields": -1
 }
} 

Eval error: nestedmap (type map[string]interface {}) is not a struct
Failed to evaluate expression - nestedmap (type map[string]interface {}) is not a struct
To client: {"seq":0,"type":"response","request_seq":13,"command":"variables","success":true,"body":{"variables":[{"name":"\"issuer\"","value":"<interface {}(map[string]interface {})>)","evaluateName":"nestedmap[\"issuer\"]","variablesReference":1002}]}}
VariablesResponse [
 {
  "name": "\"issuer\"",
  "value": "<interface {}(map[string]interface {})>)",
  "evaluateName": "nestedmap[\"issuer\"]",
  "variablesReference": 1002
 }
]

Even though evaluateName looks correct (and would trigger the right expression loading behavior if used with "Add to Watch"), the corresponding expression used as part of variable loading is incorrect (nestedmap.nestedmap[\"issuer\"]). The expression logic treats fullyQualifiedName as the parent prefix that must be combined with the variable name for a full evaluate name while in other instances throughout the code it is treated as the full evaluate name (example, example). Moreover, unlike for arrays/slices and structs, this expression does not follow the delve spec.

[polinasok]

This will need to be addressed in dlv-dap when we add on-demand variable loading for maps.

[polinasok]