gopls/internal/regtest/misc: test Implementations + vendor

This change adds a test for golang/go#56169, whose cause and fix
were the same as for golang/go#55995, which was fixed in CL 454315.

Updates golang/go#55995
Fixes golang/go#56169

Change-Id: I6d2cf964be77606de3e945c2e5ecdee82892ee99
Reviewed-on: https://go-review.googlesource.com/c/tools/+/454637
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>

Author: adonovan

gopls/internal/regtest/misc/definition_test.go

@@ -292,6 +292,7 @@ func TestGoToCrashingDefinition_Issue49223(t *testing.T) {
 // TestVendoringInvalidatesMetadata ensures that gopls uses the
 // correct metadata even after an external 'go mod vendor' command
 // causes packages to move; see issue #55995.
+// See also TestImplementationsInVendor, which tests the same fix.
 func TestVendoringInvalidatesMetadata(t *testing.T) {
 	testenv.NeedsGo1Point(t, 14)
 	const proxy = `

gopls/internal/regtest/misc/references_test.go

@@ -6,13 +6,15 @@ package misc
 
 import (
 	"fmt"
+	"os"
 	"sort"
 	"strings"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 	"golang.org/x/tools/gopls/internal/lsp/protocol"
 	. "golang.org/x/tools/gopls/internal/lsp/regtest"
+	"golang.org/x/tools/internal/testenv"
 )
 
 func TestStdlibReferences(t *testing.T) {
@@ -288,3 +290,88 @@ func _() {
 		}
 	})
 }
+
+// This is a regression test for Issue #56169, in which interface
+// implementations in vendored modules were not found. The actual fix
+// was the same as for #55995; see TestVendoringInvalidatesMetadata.
+func TestImplementationsInVendor(t *testing.T) {
+	testenv.NeedsGo1Point(t, 14)
+	const proxy = `
+-- other.com/b@v1.0.0/go.mod --
+module other.com/b
+go 1.14
+
+-- other.com/b@v1.0.0/b.go --
+package b
+type B int
+func (B) F() {}
+`
+	const src = `
+-- go.mod --
+module example.com/a
+go 1.14
+require other.com/b v1.0.0
+
+-- go.sum --
+other.com/b v1.0.0 h1:9WyCKS+BLAMRQM0CegP6zqP2beP+ShTbPaARpNY31II=
+other.com/b v1.0.0/go.mod h1:TgHQFucl04oGT+vrUm/liAzukYHNxCwKNkQZEyn3m9g=
+
+-- a.go --
+package a
+import "other.com/b"
+type I interface { F() }
+var _ b.B
+
+`
+	WithOptions(
+		ProxyFiles(proxy),
+		Modes(Default), // fails in 'experimental' mode
+	).Run(t, src, func(t *testing.T, env *Env) {
+		// Enable to debug go.sum mismatch, which may appear as
+		// "module lookup disabled by GOPROXY=off", confusingly.
+		if false {
+			env.DumpGoSum(".")
+		}
+
+		checkVendor := func(locs []protocol.Location, wantVendor bool) {
+			if len(locs) != 1 {
+				t.Errorf("got %d locations, want 1", len(locs))
+			} else if strings.Contains(string(locs[0].URI), "/vendor/") != wantVendor {
+				t.Errorf("got location %s, wantVendor=%t", locs[0], wantVendor)
+			}
+		}
+
+		env.OpenFile("a.go")
+		refPos := env.RegexpSearch("a.go", "I") // find "I" reference
+
+		// Initially, a.I has one implementation b.B in
+		// the module cache, not the vendor tree.
+		checkVendor(env.Implementations("a.go", refPos), false)
+
+		// Run 'go mod vendor' outside the editor.
+		if err := env.Sandbox.RunGoCommand(env.Ctx, ".", "mod", []string{"vendor"}, true); err != nil {
+			t.Fatalf("go mod vendor: %v", err)
+		}
+
+		// Synchronize changes to watched files.
+		env.Await(env.DoneWithChangeWatchedFiles())
+
+		// Now, b.B is found in the vendor tree.
+		checkVendor(env.Implementations("a.go", refPos), true)
+
+		// Delete the vendor tree.
+		if err := os.RemoveAll(env.Sandbox.Workdir.AbsPath("vendor")); err != nil {
+			t.Fatal(err)
+		}
+		// Notify the server of the deletion.
+		if err := env.Sandbox.Workdir.CheckForFileChanges(env.Ctx); err != nil {
+			t.Fatal(err)
+		}
+
+		// Synchronize again.
+		env.Await(env.DoneWithChangeWatchedFiles())
+
+		// b.B is once again defined in the module cache.
+		checkVendor(env.Implementations("a.go", refPos), false)
+	})
+}