From 9f574694fd3c1e3093ecf38f8e506dc6c1dc24d1 Mon Sep 17 00:00:00 2001
From: Heschi Kreinick <heschi@google.com>
Date: Wed, 5 Feb 2020 16:34:39 -0500
Subject: [PATCH] internal/imports: prevent self-imports in the stdlib

goimports has a fast path for stdlib imports that was not checking for
import cycles. Add the check.

Fixes golang/go#37063.

Change-Id: I46c98c317d8f06f83018fef9ef7edf9222e6b3f3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/217958
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
---
 internal/imports/fix.go      |  9 ++++++---
 internal/imports/fix_test.go | 21 +++++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/internal/imports/fix.go b/internal/imports/fix.go
index ac8f6b153d3..f95d0f44092 100644
--- a/internal/imports/fix.go
+++ b/internal/imports/fix.go
@@ -537,7 +537,7 @@ func getFixes(fset *token.FileSet, f *ast.File, filename string, env *ProcessEnv
 	// derive package names from import paths, see if the file is already
 	// complete. We can't add any imports yet, because we don't know
 	// if missing references are actually package vars.
-	p := &pass{fset: fset, f: f, srcDir: srcDir}
+	p := &pass{fset: fset, f: f, srcDir: srcDir, env: env}
 	if fixes, done := p.load(); done {
 		return fixes, nil
 	}
@@ -559,8 +559,7 @@ func getFixes(fset *token.FileSet, f *ast.File, filename string, env *ProcessEnv
 	}
 
 	// Third pass: get real package names where we had previously used
-	// the naive algorithm. This is the first step that will use the
-	// environment, so we provide it here for the first time.
+	// the naive algorithm.
 	p = &pass{fset: fset, f: f, srcDir: srcDir, env: env}
 	p.loadRealPackageNames = true
 	p.otherFiles = otherFiles
@@ -853,6 +852,10 @@ func cmdDebugStr(cmd *exec.Cmd) string {
 
 func addStdlibCandidates(pass *pass, refs references) {
 	add := func(pkg string) {
+		// Prevent self-imports.
+		if path.Base(pkg) == pass.f.Name.Name && filepath.Join(pass.env.GOROOT, "src", pkg) == pass.srcDir {
+			return
+		}
 		exports := copyExports(stdlib[pkg])
 		pass.addCandidate(
 			&ImportInfo{ImportPath: pkg},
diff --git a/internal/imports/fix_test.go b/internal/imports/fix_test.go
index 6e83527d31a..f2bc5b639a2 100644
--- a/internal/imports/fix_test.go
+++ b/internal/imports/fix_test.go
@@ -1577,6 +1577,27 @@ var _ = bytes.Buffer
 	})
 }
 
+func TestStdlibSelfImports(t *testing.T) {
+	const input = `package ecdsa
+
+var _ = ecdsa.GenerateKey
+`
+
+	testConfig{
+		module: packagestest.Module{
+			Name: "ignored.com",
+		},
+	}.test(t, func(t *goimportTest) {
+		got, err := t.processNonModule(filepath.Join(t.env.GOROOT, "src/crypto/ecdsa/foo.go"), []byte(input), nil)
+		if err != nil {
+			t.Fatalf("Process() = %v", err)
+		}
+		if string(got) != input {
+			t.Errorf("Got:\n%s\nWant:\n%s", got, input)
+		}
+	})
+}
+
 type testConfig struct {
 	gopathOnly bool
 	module     packagestest.Module