Allow to customize user functions in rule error-strings (#703)

* Allow to customize user functions in rule `error-strings`

* Rollback the Available Rules table format in README

* adds memoization of the rule's configuration

Co-authored-by: chavacava <salvadorcavadini+github@gmail.com>

README.md

@@ -350,6 +350,8 @@ enableAllRules = true
     Arguments = [7]
 [rule.function-result-limit]
     Arguments = [3]
+[rule.error-strings]
+    Arguments = ["mypackage.Error"]
 ```
 
 ### Default Configuration
@@ -410,7 +412,6 @@ warningCode = 0
 ## Available Rules
 
 List of all available rules. The rules ported from `golint` are left unchanged and indicated in the `golint` column.
-
 | Name                  | Config | Description                                                      | `golint` | Typed |
 | --------------------- | :----: | :--------------------------------------------------------------- | :------: | :---: |
 | [`context-keys-type`](./RULES_DESCRIPTIONS.md#context-key-types)   |  n/a   | Disallows the usage of basic types in `context.WithValue`.       |   yes    |  yes  |
@@ -423,7 +424,7 @@ List of all available rules. The rules ported from `golint` are left unchanged a
 | [`context-as-argument`](./RULES_DESCRIPTIONS.md#context-as-argument) |  n/a   | `context.Context` should be the first argument of a function.    |   yes    |  no   |
 | [`dot-imports`](./RULES_DESCRIPTIONS.md#dot-imports)         |  n/a   | Forbids `.` imports.                                             |   yes    |  no   |
 | [`error-return`](./RULES_DESCRIPTIONS.md#error-return)        |  n/a   | The error return parameter should be last.                       |   yes    |  no   |
-| [`error-strings`](./RULES_DESCRIPTIONS.md#error-strings)       |  n/a   | Conventions around error strings.                                |   yes    |  no   |
+| [`error-strings`](./RULES_DESCRIPTIONS.md#error-strings)       |  []string   | Conventions around error strings.                                |   yes    |  no   |
 | [`error-naming`](./RULES_DESCRIPTIONS.md#error-naming)        |  n/a   | Naming of error variables.                                       |   yes    |  no   |
 | [`exported`](./RULES_DESCRIPTIONS.md#exported)            |  []string   | Naming and commenting conventions on exported symbols.           |   yes    |  no   |
 | [`if-return`](./RULES_DESCRIPTIONS.md#if-return)           |  n/a   | Redundant if when returning an error.                            |   no    |  no   |

rule/error-strings.go

@@ -4,20 +4,29 @@ import (
 	"go/ast"
 	"go/token"
 	"strconv"
+	"strings"
+	"sync"
 	"unicode"
 	"unicode/utf8"
 
 	"github.com/mgechev/revive/lint"
 )
 
 // ErrorStringsRule lints given else constructs.
-type ErrorStringsRule struct{}
+type ErrorStringsRule struct {
+	errorFunctions map[string]map[string]struct{}
+	sync.Mutex
+}
 
-// Apply applies the rule to given file.
-func (*ErrorStringsRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
-	var failures []lint.Failure
+func (r *ErrorStringsRule) configure(arguments lint.Arguments) {
+	r.Lock()
+	defer r.Unlock()
 
-	errorFunctions := map[string]map[string]struct{}{
+	if r.errorFunctions != nil {
+		return
+	}
+
+	r.errorFunctions = map[string]map[string]struct{}{
 		"fmt": {
 			"Errorf": {},
 		},
@@ -31,11 +40,33 @@ func (*ErrorStringsRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure
 		},
 	}
 
+	var invalidCustomFunctions []string
+	for _, argument := range arguments {
+		if functionName, ok := argument.(string); ok {
+			fields := strings.Split(strings.TrimSpace(functionName), ".")
+			if len(fields) != 2 || len(fields[0]) == 0 || len(fields[1]) == 0 {
+				invalidCustomFunctions = append(invalidCustomFunctions, functionName)
+				continue
+			}
+			r.errorFunctions[fields[0]] = map[string]struct{}{fields[1]: {}}
+		}
+	}
+	if len(invalidCustomFunctions) != 0 {
+		panic("found invalid custom function: " + strings.Join(invalidCustomFunctions, ","))
+	}
+}
+
+// Apply applies the rule to given file.
+func (r *ErrorStringsRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	r.configure(arguments)
+
 	fileAst := file.AST
 	walker := lintErrorStrings{
 		file:           file,
 		fileAst:        fileAst,
-		errorFunctions: errorFunctions,
+		errorFunctions: r.errorFunctions,
 		onFailure: func(failure lint.Failure) {
 			failures = append(failures, failure)
 		},

test/error-strings-custom-functions_test.go

@@ -0,0 +1,15 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/lint"
+	"github.com/mgechev/revive/rule"
+)
+
+func TestErrorStringsWithCustomFunctions(t *testing.T) {
+	args := []interface{}{"pkgErrors.Wrap"}
+	testRule(t, "error-strings-with-custom-functions", &rule.ErrorStringsRule{}, &lint.RuleConfig{
+		Arguments: args,
+	})
+}

testdata/error-strings-with-custom-functions.go

@@ -0,0 +1,12 @@
+package fixtures
+
+import (
+	pkgErrors "github.com/pkg/errors"
+)
+
+// Check for the error strings themselves.
+
+func errorsStrings(x int) error {
+	var err error
+	return pkgErrors.Wrap(err, "This %d is too low") // MATCH /error strings should not be capitalized or end with punctuation or a newline/
+}