internal/lsp: handle exclude directives in multi-module mode

Add exclude directives to the workspace module go.mod file.

Fixes golang/go#44932

Change-Id: I93f587b321dc6b35e7df30ea39cf8f70f656d04c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/317449
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/internal/regtest/workspace/workspace_test.go

@@ -242,6 +242,66 @@ func Hello() int {
 	})
 }
 
+func TestMultiModuleWithExclude(t *testing.T) {
+	testenv.NeedsGo1Point(t, 16)
+
+	const proxy = `
+-- c.com@v1.2.3/go.mod --
+module c.com
+
+go 1.12
+
+require b.com v1.2.3
+-- c.com@v1.2.3/blah/blah.go --
+package blah
+
+func SaySomething() {
+	fmt.Println("something")
+}
+-- b.com@v1.2.3/go.mod --
+module b.com
+
+go 1.12
+-- b.com@v1.2.4/b/b.go --
+package b
+
+func Hello() {}
+-- b.com@v1.2.4/go.mod --
+module b.com
+
+go 1.12
+-- b.com@v1.2.4/b/b.go --
+package b
+
+func Hello() {}
+`
+	const multiModule = `
+-- go.mod --
+module a.com
+
+require c.com v1.2.3
+
+exclude b.com v1.2.3
+-- go.sum --
+c.com v1.2.3 h1:n07Dz9fYmpNqvZMwZi5NEqFcSHbvLa9lacMX+/g25tw=
+c.com v1.2.3/go.mod h1:/4TyYgU9Nu5tA4NymP5xyqE8R2VMzGD3TbJCwCOvHAg=
+-- main.go --
+package a
+
+func main() {
+	var x int
+}
+`
+	WithOptions(
+		ProxyFiles(proxy),
+		Modes(Experimental),
+	).Run(t, multiModule, func(t *testing.T, env *Env) {
+		env.Await(
+			env.DiagnosticAtRegexp("main.go", "x"),
+		)
+	})
+}
+
 // This change tests that the version of the module used changes after it has
 // been deleted from the workspace.
 func TestDeleteModule_Interdependent(t *testing.T) {

internal/lsp/cache/snapshot.go

@@ -1810,7 +1810,8 @@ func buildWorkspaceModFile(ctx context.Context, modFiles map[span.URI]struct{},
 	// Fall back to 1.12 -- old versions insist on having some version.
 	goVersion := "1.12"
 
-	paths := make(map[string]span.URI)
+	paths := map[string]span.URI{}
+	excludes := map[string][]string{}
 	var sortedModURIs []span.URI
 	for uri := range modFiles {
 		sortedModURIs = append(sortedModURIs, uri)
@@ -1853,6 +1854,9 @@ func buildWorkspaceModFile(ctx context.Context, modFiles map[span.URI]struct{},
 		if err := file.AddReplace(path, "", dirURI(modURI).Filename(), ""); err != nil {
 			return nil, err
 		}
+		for _, exclude := range parsed.Exclude {
+			excludes[exclude.Mod.Path] = append(excludes[exclude.Mod.Path], exclude.Mod.Version)
+		}
 	}
 	if goVersion != "" {
 		file.AddGoStmt(goVersion)
@@ -1896,6 +1900,11 @@ func buildWorkspaceModFile(ctx context.Context, modFiles map[span.URI]struct{},
 			}
 		}
 	}
+	for path, versions := range excludes {
+		for _, version := range versions {
+			file.AddExclude(path, version)
+		}
+	}
 	file.SortBlocks()
 	return file, nil
 }