New rule: duplicated-imports (#111)

* Adds rule superfluous-else (an extension of indent-error-flow)

* Fix superfluous-else rule struct namming.

* Adds superfuous-else rule to the rules table

* Adds confusing-naming rule

* adds multifile test

* clean-up

* fix config.go

* clean master

* new ADS rule: newerr

* ADS-print working version

* ads-print final version

* ads-lost-err working version

* adds duplicated-imports rule

* adds duplicated-imports rule

README.md

@@ -292,6 +292,7 @@ List of all available rules. The rules ported from `golint` are left unchanged a
 | [`empty-lines`](./RULES_DESCRIPTIONS.md#empty-lines)   | n/a | Warns when there are heading or trailing newlines in a block              |    no    |  no   |
 | [`line-length-limit`](./RULES_DESCRIPTIONS.md#line-length-limit)   | int    | Specifies the maximum number of characters in a line             |    no    |  no   |
 | [`call-to-gc`](./RULES_DESCRIPTIONS.md#call-to-gc)   | n/a    | Warns on explicit call to the garbage collector    |    no    |  no   |
+| [`duplicated-imports`](./RULES_DESCRIPTIONS#duplicated-imports) | n/a  | Looks for packages that are imported two or more times   |    no    |  no   |
 
 ## Configurable rules
 

RULES_DESCRIPTIONS.md

@@ -18,6 +18,7 @@ List of all available rules.
   - [cyclomatic](#cyclomatic)
   - [deep-exit](#deep-exit)
   - [dot-imports](#dot-imports)
+  - [duplicated-imports](#duplicated-imports)
   - [empty-block](#empty-block)
   - [empty-lines](#empty-lines)
   - [error-naming](#error-naming)
@@ -168,6 +169,12 @@ More information [here](https://github.com/golang/go/wiki/CodeReviewComments#imp
 
 _Configuration_: N/A
 
+## duplicated-imports
+
+_Description_: It is possible to unintentionally import the same package twice. This rule looks for packages that are imported two or more times.
+
+_Configuration_: N/A
+
 ## empty-block
 
 _Description_: Empty blocks make code less readable and could be a symptom of a bug or unfinished refactoring.

config.go

@@ -73,6 +73,7 @@ var allRules = append([]lint.Rule{
 	&rule.EmptyLinesRule{},
 	&rule.LineLengthLimitRule{},
 	&rule.CallToGCRule{},
+	&rule.DuplicatedImportsRule{},
 }, defaultRules...)
 
 var allFormatters = []lint.Formatter{

fixtures/duplicated-imports.go

@@ -0,0 +1,8 @@
+package fixtures
+
+import(
+	"crypto/md5"  
+        "strings"
+        _ "crypto/md5" // MATCH /Package "crypto/md5" already imported/
+        str "strings"  // MATCH /Package "strings" already imported/
+)

rule/duplicated-imports.go

@@ -0,0 +1,39 @@
+package rule
+
+import (
+	"fmt"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// DuplicatedImportsRule lints given else constructs.
+type DuplicatedImportsRule struct{}
+
+// Apply applies the rule to given file.
+func (r *DuplicatedImportsRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+
+	impPaths := map[string]struct{}{}
+	for _, imp := range file.AST.Imports {
+		path := imp.Path.Value
+		_, ok := impPaths[path]
+		if ok {
+			failures = append(failures, lint.Failure{
+				Confidence: 1,
+				Failure:    fmt.Sprintf("Package %s already imported", path),
+				Node:       imp,
+				Category:   "imports",
+			})
+			continue
+		}
+
+		impPaths[path] = struct{}{}
+	}
+
+	return failures
+}
+
+// Name returns the rule name.
+func (r *DuplicatedImportsRule) Name() string {
+	return "duplicated-imports"
+}

test/duplicated-import_test.go

@@ -0,0 +1,11 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/rule"
+)
+
+func TestDuplicatedImports(t *testing.T) {
+	testRule(t, "duplicated-imports", &rule.DuplicatedImportsRule{})
+}