revive/rule/context_as_argument.go

package rule

import (
	"fmt"
	"go/ast"
	"strings"
	"sync"

	"github.com/mgechev/revive/lint"
)

// ContextAsArgumentRule suggests that `context.Context` should be the first argument of a function.
type ContextAsArgumentRule struct {
	allowTypes map[string]struct{}

	configureOnce sync.Once
}

// Apply applies the rule to given file.
func (r *ContextAsArgumentRule) Apply(file *lint.File, args lint.Arguments) []lint.Failure {
	r.configureOnce.Do(func() { r.configure(args) })

	var failures []lint.Failure
	for _, decl := range file.AST.Decls {
		fn, ok := decl.(*ast.FuncDecl)
		if !ok || len(fn.Type.Params.List) <= 1 {
			continue // not a function or a function with less than 2 parameters
		}

		fnArgs := fn.Type.Params.List

		// A context.Context should be the first parameter of a function.
		// Flag any that show up after the first.
		isCtxStillAllowed := true
		for _, arg := range fnArgs {
			argIsCtx := isPkgDot(arg.Type, "context", "Context")
			if argIsCtx && !isCtxStillAllowed {
				failures = append(failures, lint.Failure{
					Node:       arg,
					Category:   "arg-order",
					Failure:    "context.Context should be the first parameter of a function",
					Confidence: 0.9,
				})

				break // only flag one
			}

			typeName := gofmt(arg.Type)
			// a parameter of type context.Context is still allowed if the current arg type is in the allow types LookUpTable
			_, isCtxStillAllowed = r.allowTypes[typeName]
		}
	}

	return failures
}

// Name returns the rule name.
func (*ContextAsArgumentRule) Name() string {
	return "context-as-argument"
}

func (r *ContextAsArgumentRule) configure(arguments lint.Arguments) {
	r.allowTypes = r.getAllowTypesFromArguments(arguments)
}

func (r *ContextAsArgumentRule) getAllowTypesFromArguments(args lint.Arguments) map[string]struct{} {
	allowTypesBefore := []string{}
	if len(args) >= 1 {
		argKV, ok := args[0].(map[string]any)
		if !ok {
			panic(fmt.Sprintf("Invalid argument to the context-as-argument rule. Expecting a k,v map, got %T", args[0]))
		}
		for k, v := range argKV {
			switch k {
			case "allowTypesBefore":
				typesBefore, ok := v.(string)
				if !ok {
					panic(fmt.Sprintf("Invalid argument to the context-as-argument.allowTypesBefore rule. Expecting a string, got %T", v))
				}
				allowTypesBefore = append(allowTypesBefore, strings.Split(typesBefore, ",")...)
			default:
				panic(fmt.Sprintf("Invalid argument to the context-as-argument rule. Unrecognized key %s", k))
			}
		}
	}

	result := make(map[string]struct{}, len(allowTypesBefore))
	for _, v := range allowTypesBefore {
		result[v] = struct{}{}
	}

	result["context.Context"] = struct{}{} // context.Context is always allowed before another context.Context
	return result
}