internal/imports: remove duplicate unused imports

Track imports per identifier as a slice to accommodate duplicates. This
allows us to generate multiple import fixes per import identifier.

Fixes golang/go#45398

internal/imports/fix.go

@@ -252,7 +252,7 @@ type pass struct {
 	otherFiles           []*ast.File    // sibling files.
 
 	// Intermediate state, generated by load.
-	existingImports map[string]*ImportInfo
+	existingImports map[string][]*ImportInfo
 	allRefs         references
 	missingRefs     references
 
@@ -317,7 +317,7 @@ func (p *pass) importIdentifier(imp *ImportInfo) string {
 func (p *pass) load() ([]*ImportFix, bool) {
 	p.knownPackages = map[string]*packageInfo{}
 	p.missingRefs = references{}
-	p.existingImports = map[string]*ImportInfo{}
+	p.existingImports = map[string][]*ImportInfo{}
 
 	// Load basic information about the file in question.
 	p.allRefs = collectReferences(p.f)
@@ -348,7 +348,7 @@ func (p *pass) load() ([]*ImportFix, bool) {
 		}
 	}
 	for _, imp := range imports {
-		p.existingImports[p.importIdentifier(imp)] = imp
+		p.existingImports[p.importIdentifier(imp)] = append(p.existingImports[p.importIdentifier(imp)], imp)
 	}
 
 	// Find missing references.
@@ -387,31 +387,33 @@ func (p *pass) fix() ([]*ImportFix, bool) {
 
 	// Found everything, or giving up. Add the new imports and remove any unused.
 	var fixes []*ImportFix
-	for _, imp := range p.existingImports {
-		// We deliberately ignore globals here, because we can't be sure
-		// they're in the same package. People do things like put multiple
-		// main packages in the same directory, and we don't want to
-		// remove imports if they happen to have the same name as a var in
-		// a different package.
-		if _, ok := p.allRefs[p.importIdentifier(imp)]; !ok {
-			fixes = append(fixes, &ImportFix{
-				StmtInfo:  *imp,
-				IdentName: p.importIdentifier(imp),
-				FixType:   DeleteImport,
-			})
-			continue
-		}
+	for _, identifierImports := range p.existingImports {
+		for _, imp := range identifierImports {
+			// We deliberately ignore globals here, because we can't be sure
+			// they're in the same package. People do things like put multiple
+			// main packages in the same directory, and we don't want to
+			// remove imports if they happen to have the same name as a var in
+			// a different package.
+			if _, ok := p.allRefs[p.importIdentifier(imp)]; !ok {
+				fixes = append(fixes, &ImportFix{
+					StmtInfo:  *imp,
+					IdentName: p.importIdentifier(imp),
+					FixType:   DeleteImport,
+				})
+				continue
+			}
 
-		// An existing import may need to update its import name to be correct.
-		if name := p.importSpecName(imp); name != imp.Name {
-			fixes = append(fixes, &ImportFix{
-				StmtInfo: ImportInfo{
-					Name:       name,
-					ImportPath: imp.ImportPath,
-				},
-				IdentName: p.importIdentifier(imp),
-				FixType:   SetImportName,
-			})
+			// An existing import may need to update its import name to be correct.
+			if name := p.importSpecName(imp); name != imp.Name {
+				fixes = append(fixes, &ImportFix{
+					StmtInfo: ImportInfo{
+						Name:       name,
+						ImportPath: imp.ImportPath,
+					},
+					IdentName: p.importIdentifier(imp),
+					FixType:   SetImportName,
+				})
+			}
 		}
 	}
 

internal/imports/fix_test.go

@@ -1151,6 +1151,19 @@ var _, _ = rand.Read, rand.NewZipf
 import "math/rand"
 
 var _, _ = rand.Read, rand.NewZipf
+`,
+	},
+	{
+		name: "unused_duplicate_imports_remove",
+		in: `package main
+
+import (
+	"errors"
+
+	"github.com/pkg/errors"
+)
+`,
+		out: `package main
 `,
 	},
 }