From 70ccf57e4b75514eaa0d0b35525b2b5fd63e489a Mon Sep 17 00:00:00 2001
From: aarzilli <alessandro.arzilli@gmail.com>
Date: Fri, 3 Dec 2021 10:51:49 +0100
Subject: [PATCH] go/packages: fix loading single file when outside of GOPATH,
 module

Allows a 'file=' query to load a single file even when it is outside of
GOPATH or a module.

Fixes golang/go#49949

Change-Id: I519f1412923dfc1d2504ec49620d10c823e5c0dc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/369014
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
---
 go/packages/golist.go        |  7 ++++---
 go/packages/packages_test.go | 25 +++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/go/packages/golist.go b/go/packages/golist.go
index 50533995a6..de881562de 100644
--- a/go/packages/golist.go
+++ b/go/packages/golist.go
@@ -302,11 +302,12 @@ func (state *golistState) runContainsQueries(response *responseDeduper, queries
 		}
 		dirResponse, err := state.createDriverResponse(pattern)
 
-		// If there was an error loading the package, or the package is returned
-		// with errors, try to load the file as an ad-hoc package.
+		// If there was an error loading the package, or no packages are returned,
+		// or the package is returned with errors, try to load the file as an
+		// ad-hoc package.
 		// Usually the error will appear in a returned package, but may not if we're
 		// in module mode and the ad-hoc is located outside a module.
-		if err != nil || len(dirResponse.Packages) == 1 && len(dirResponse.Packages[0].GoFiles) == 0 &&
+		if err != nil || len(dirResponse.Packages) == 0 || len(dirResponse.Packages) == 1 && len(dirResponse.Packages[0].GoFiles) == 0 &&
 			len(dirResponse.Packages[0].Errors) == 1 {
 			var queryErr error
 			if dirResponse, queryErr = state.adhocPackage(pattern, query); queryErr != nil {
diff --git a/go/packages/packages_test.go b/go/packages/packages_test.go
index 796edb6b7b..647f3a366d 100644
--- a/go/packages/packages_test.go
+++ b/go/packages/packages_test.go
@@ -2709,6 +2709,31 @@ func TestEmptyEnvironment(t *testing.T) {
 	}
 }
 
+func TestPackageLoadSingleFile(t *testing.T) {
+	tmp, err := ioutil.TempDir("", "a")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmp)
+
+	filename := filepath.Join(tmp, "a.go")
+
+	if err := ioutil.WriteFile(filename, []byte(`package main; func main() { println("hello world") }`), 0775); err != nil {
+		t.Fatal(err)
+	}
+
+	pkgs, err := packages.Load(&packages.Config{Mode: packages.LoadSyntax, Dir: tmp}, "file="+filename)
+	if err != nil {
+		t.Fatalf("could not load package: %v", err)
+	}
+	if len(pkgs) != 1 {
+		t.Fatalf("expected one package to be loaded, got %d", len(pkgs))
+	}
+	if len(pkgs[0].CompiledGoFiles) != 1 || pkgs[0].CompiledGoFiles[0] != filename {
+		t.Fatalf("expected one compiled go file (%q), got %v", filename, pkgs[0].CompiledGoFiles)
+	}
+}
+
 func errorMessages(errors []packages.Error) []string {
 	var msgs []string
 	for _, err := range errors {