internal/refactor/inline: improve package local name by preserving alias

The existing implementation generates package local names by appending
a numeric suffix to package name, which reduces readability.

This improvement preserves existing import alias when available and
fall back to the existing name generation mechanism if a conflict occurs.

Updates golang/go#63352
Fixes golang/go#74965

Signed-off-by: Gavin Lam <gavin.oss@tutamail.com>

Author: gavinkflam

internal/refactor/inline/inline.go

@@ -491,14 +491,10 @@ func (i *importState) importName(pkgPath string, shadow shadowMap) string {
 	return ""
 }
 
-// localName returns the local name for a given imported package path,
-// adding one if it doesn't exists.
-func (i *importState) localName(pkgPath, pkgName string, shadow shadowMap) string {
-	// Does an import already exist that works in this shadowing context?
-	if name := i.importName(pkgPath, shadow); name != "" {
-		return name
-	}
-
+// findNewLocalName returns a new local name to use in a particular shadowing
+// context. It considers the existing package alias, or construct a new alias
+// based on the package name.
+func (i *importState) findNewLocalName(pkgName, pkgAlias string, shadow shadowMap) string {
 	newlyAdded := func(name string) bool {
 		return slices.ContainsFunc(i.newImports, func(n newImport) bool { return n.pkgName == name })
 	}
@@ -516,20 +512,35 @@ func (i *importState) localName(pkgPath, pkgName string, shadow shadowMap) strin
 
 	// import added by callee
 	//
-	// Choose local PkgName based on last segment of
+	// Try to preserve the package alias first.
+	//
+	// If that is shadowed, choose local PkgName based on last segment of
 	// package path plus, if needed, a numeric suffix to
 	// ensure uniqueness.
 	//
 	// "init" is not a legal PkgName.
-	//
-	// TODO(rfindley): is it worth preserving local package names for callee
-	// imports? Are they likely to be better or worse than the name we choose
-	// here?
+	if shadow[pkgAlias] == 0 && !shadowedInCaller(pkgAlias) && !newlyAdded(pkgAlias) && pkgAlias != "init" {
+		return pkgAlias
+	}
+
 	base := pkgName
 	name := base
 	for n := 0; shadow[name] != 0 || shadowedInCaller(name) || newlyAdded(name) || name == "init"; n++ {
 		name = fmt.Sprintf("%s%d", base, n)
 	}
+
+	return name
+}
+
+// localName returns the local name for a given imported package path,
+// adding one if it doesn't exists.
+func (i *importState) localName(pkgPath, pkgName, pkgAlias string, shadow shadowMap) string {
+	// Does an import already exist that works in this shadowing context?
+	if name := i.importName(pkgPath, shadow); name != "" {
+		return name
+	}
+
+	name := i.findNewLocalName(pkgName, pkgAlias, shadow)
 	i.logf("adding import %s %q", name, pkgPath)
 	spec := &ast.ImportSpec{
 		Path: &ast.BasicLit{
@@ -1338,7 +1349,7 @@ func (st *state) renameFreeObjs(istate *importState) ([]ast.Expr, error) {
 		var newName ast.Expr
 		if obj.Kind == "pkgname" {
 			// Use locally appropriate import, creating as needed.
-			n := istate.localName(obj.PkgPath, obj.PkgName, obj.Shadow)
+			n := istate.localName(obj.PkgPath, obj.PkgName, obj.Name, obj.Shadow)
 			newName = makeIdent(n) // imported package
 		} else if !obj.ValidPos {
 			// Built-in function, type, or value (e.g. nil, zero):
@@ -1383,7 +1394,7 @@ func (st *state) renameFreeObjs(istate *importState) ([]ast.Expr, error) {
 
 			// Form a qualified identifier, pkg.Name.
 			if qualify {
-				pkgName := istate.localName(obj.PkgPath, obj.PkgName, obj.Shadow)
+				pkgName := istate.localName(obj.PkgPath, obj.PkgName, obj.PkgName, obj.Shadow)
 				newName = &ast.SelectorExpr{
 					X:   makeIdent(pkgName),
 					Sel: makeIdent(obj.Name),

internal/refactor/inline/testdata/assignment.txtar

@@ -126,11 +126,11 @@ func _() {
 package a
 
 import (
-	"testdata/c"
-	c0 "testdata/c2"
+	c1 "testdata/c"
+	c2 "testdata/c2"
 )
 
 func _() {
-	x, y := c.C(0), c0.C(1) //@ inline(re"B", b4)
+	x, y := c1.C(0), c2.C(1) //@ inline(re"B", b4)
 	_, _ = x, y
 }

internal/refactor/inline/testdata/import-preserve-alias.txtar

@@ -0,0 +1,56 @@
+Test of inlining a function and preserve the imported package alias.
+
+-- go.mod --
+module example.com
+go 1.19
+
+-- main/main.go --
+package main
+
+import stringutil "example.com/string/util"
+import "example.com/util"
+
+func main() {
+	util.A() //@ inline(re"A", result)
+	stringutil.B()
+}
+
+-- util/util.go --
+package util
+
+import stringutil "example.com/string/util"
+import urlutil "example.com/url/util"
+
+func A() {
+	stringutil.A()
+	urlutil.A()
+}
+
+-- string/util/util.go --
+package util
+
+func A() {
+}
+
+func B() {
+}
+
+-- url/util/util.go --
+package util
+
+func A() {
+}
+
+-- result --
+package main
+
+import (
+	stringutil "example.com/string/util"
+	urlutil "example.com/url/util"
+)
+
+func main() {
+	stringutil.A()
+	urlutil.A() //@ inline(re"A", result)
+	stringutil.B()
+}

internal/refactor/inline/testdata/issue63298.txtar

@@ -38,11 +38,11 @@ func B() {}
 package a
 
 import (
-	b0 "testdata/another/b"
+	anotherb "testdata/another/b"
 	"testdata/b"
 )
 
 func _() {
 	b.B()
-	b0.B() //@ inline(re"a2", result)
+	anotherb.B() //@ inline(re"a2", result)
 }