Add diagnostic capability

[uudashr]

TL;DR:

• Add flag -d to binary cli to show diagnostics
• Add functions to support diagnostics to the API
  • ComplexityStatsWithDiagnostic(...) []Stat
  • ScanComplexity(...) ScanResult

---

Diagnostic enable us to understand the details how the complexity increase.

Example source code:

package prime

func SumOfPrimes(max int) int {
        var total int

OUT:
        for i := 1; i < max; i++ { // +1
                for j := 2; j < i; j++ { // +2 (nesting = 1)
                        if i%j == 0 { // +3 (nesting = 2)
                                continue OUT // +1
                        }
                }
                total += i
        }

        return total
} // Cognitive complexity = 7

By supplying -d flag on the command line ex: gocognit -json -d ., it will show diagnostics information:

[
    {
        "PkgName": "prime",
        "FuncName": "SumOfPrimes",
        "Complexity": 7,
        "Pos": {
            "Filename": "prime.go",
            "Offset": 15,
            "Line": 3,
            "Column": 1
        },
        "Diagnostics": [
            {
                "Inc": 1,
                "Text": "for",
                "Pos": {
                    "Offset": 69,
                    "Line": 7,
                    "Column": 2
                }
            },
            {
                "Inc": 2,
                "Nesting": 1,
                "Text": "for",
                "Pos": {
                    "Offset": 104,
                    "Line": 8,
                    "Column": 3
                }
            },
            {
                "Inc": 3,
                "Nesting": 2,
                "Text": "if",
                "Pos": {
                    "Offset": 152,
                    "Line": 9,
                    "Column": 4
                }
            },
            {
                "Inc": 1,
                "Text": "continue",
                "Pos": {
                    "Offset": 190,
                    "Line": 10,
                    "Column": 5
                }
            }
        ]
    }
]

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 suggestion.

Comments skipped due to low confidence (3)

README.md:201

• The type 'Diagnostics' should be 'Diagnostic' to match the type definition.

Diagnostics []Diagnostics

gocognit.go:20

• The field name 'Diagnostics' should be singular to match the type name 'Diagnostic'.

Diagnostics []Diagnostic `json:",omitempty"`

gocognit.go:103

• [nitpick] The variable name 'tracePos' should be renamed to 'diagPos' to better reflect its purpose.

func generateDiagnostics(fset *token.FileSet, diags []diagnostic) []Diagnostic {