From f5dab9fca4a79dceb72d10394408af5cb6ad5898 Mon Sep 17 00:00:00 2001
From: Duco van Amstel <duco.vanamstel@gmail.com>
Date: Thu, 28 Feb 2019 18:10:58 +0000
Subject: [PATCH] checkers: add dupImports checker (#814)

---
 checkers/dupImports_checker.go                | 76 +++++++++++++++++++
 .../testdata/dupImports/negative_tests.go     |  9 +++
 .../testdata/dupImports/positive_tests.go     | 17 +++++
 3 files changed, 102 insertions(+)
 create mode 100644 checkers/dupImports_checker.go
 create mode 100644 checkers/testdata/dupImports/negative_tests.go
 create mode 100644 checkers/testdata/dupImports/positive_tests.go

diff --git a/checkers/dupImports_checker.go b/checkers/dupImports_checker.go
new file mode 100644
index 000000000..7a6c837c6
--- /dev/null
+++ b/checkers/dupImports_checker.go
@@ -0,0 +1,76 @@
+package checkers
+
+import (
+	"fmt"
+	"go/ast"
+
+	"github.com/go-lintpack/lintpack"
+)
+
+func init() {
+	var info lintpack.CheckerInfo
+	info.Name = "dupImports"
+	info.Tags = []string{"style", "experimental"}
+	info.Summary = "Detects multiple imports of the same package under different aliases."
+	info.Before = `
+import (
+	"fmt"
+	priting "fmt"
+)
+
+func helloWorld() {
+	fmt.Println("Hello")
+	printing.Println("World")
+}`
+	info.After = `
+import(
+	"fmt"
+)
+
+func helloWorld() {
+	fmt.Println("Hello")
+	fmt.Println("World")
+}`
+
+	collection.AddChecker(&info, func(ctx *lintpack.CheckerContext) lintpack.FileWalker {
+		return &dupImportChecker{ctx: ctx}
+	})
+}
+
+type dupImportChecker struct {
+	ctx *lintpack.CheckerContext
+}
+
+func (c *dupImportChecker) WalkFile(f *ast.File) {
+	imports := make(map[string][]*ast.ImportSpec)
+	for _, importDcl := range f.Imports {
+		pkg := importDcl.Path.Value
+		imports[pkg] = append(imports[pkg], importDcl)
+	}
+
+	fPos := c.ctx.FileSet.File(f.Pos())
+	if fPos == nil {
+		// Bail out if we can't, for any reason, determine
+		// the source file we are dealing with.
+		return
+	}
+	for _, importList := range imports {
+		if len(importList) == 1 {
+			continue
+		}
+
+		msg := fmt.Sprintf("package is imported %d times under different aliases on lines", len(importList))
+		for idx, importDcl := range importList {
+			switch {
+			case idx == len(importList)-1:
+				msg += " and"
+			case idx > 0:
+				msg += ","
+			}
+			msg += fmt.Sprintf(" %d", fPos.Line(importDcl.Pos()))
+		}
+		for _, importDcl := range importList {
+			c.ctx.Warn(importDcl, msg)
+		}
+	}
+}
diff --git a/checkers/testdata/dupImports/negative_tests.go b/checkers/testdata/dupImports/negative_tests.go
new file mode 100644
index 000000000..833b862ef
--- /dev/null
+++ b/checkers/testdata/dupImports/negative_tests.go
@@ -0,0 +1,9 @@
+package checker_test
+
+import "fmt"
+
+func negativeHelloworld() {
+	fmt.Println("Hello")
+	fmt.Println("Shiny")
+	fmt.Println("World")
+}
diff --git a/checkers/testdata/dupImports/positive_tests.go b/checkers/testdata/dupImports/positive_tests.go
new file mode 100644
index 000000000..b1740446b
--- /dev/null
+++ b/checkers/testdata/dupImports/positive_tests.go
@@ -0,0 +1,17 @@
+package checker_test
+
+/*! package is imported 3 times under different aliases on lines 4, 8 and 10 */
+import printing "fmt"
+
+import (
+	/*! package is imported 3 times under different aliases on lines 4, 8 and 10 */
+	"fmt"
+	/*! package is imported 3 times under different aliases on lines 4, 8 and 10 */
+	print "fmt"
+)
+
+func positiveHelloworld() {
+	fmt.Println("Hello")
+	print.Println("Shiny")
+	printing.Println("World")
+}