fix(internal/librarian): join protobuf-src subdir before passing down to sidekick (#3279)

This is a fix to follow-up on revert
#3277. Now it combines
protobuf root dir and subdir before passing down to sidekick config as
"protobuf-src-root".

Issue with implementation before revert: pass down both
`protobuf-src-root` and `protobuf-src-subdir` to sidekick, combine the
path in `protoc` when constructing protoc command. This was fine, but
sidekick flow joins path before this point in
[overrideSources](https://github.com/googleapis/librarian/blob/b405072f6a4f72adcc3ff299cb13de6bbe3d4327/internal/sidekick/sidekick/refreshall.go#L60),
but somehow kept `-subdir` config at a later point (Not totally clear
when, likely during a merge, need a bit more digging), then results in
`proto/path/subdir/subdir`.

Now: `librarian generate` comibines path after downloading, before
translating to sidekick config. `sidekick refresh` continue to do the
join in `overrideSources`. This code is not shared with librarian, so
logic not repeated.

Alternative: Keep path join logic within `protoc` function and remove
joins in librarian and `overrideSources`. Did not choose because wanted
to limit impact for sidekick codepath to avoid unexpected behaviors.

Fix #3183

Author: zhumin8

internal/librarian/internal/rust/codec.go

@@ -15,6 +15,7 @@
 package rust
 
 import (
+	"path"
 	"strings"
 
 	"github.com/googleapis/librarian/internal/config"
@@ -38,22 +39,18 @@ func toSidekickConfig(library *config.Library, channel *config.Channel, googleap
 	} else {
 		source["roots"] = strings.Join(library.Roots, ",")
 		rootMap := map[string]struct {
-			path   string
-			subdir string
-			keys   []string
+			path string
+			key  string
 		}{
-			"googleapis":   {path: googleapisDir, keys: []string{"googleapis-root"}},
-			"discovery":    {path: discoveryDir, keys: []string{"discovery-root"}},
-			"showcase":     {path: showcaseDir, keys: []string{"showcase-root"}},
-			"protobuf-src": {path: protobufRootDir, subdir: protobufSubDir, keys: []string{"protobuf-src-root", "protobuf-src-subdir"}},
-			"conformance":  {path: conformanceDir, keys: []string{"conformance-root"}},
+			"googleapis":   {path: googleapisDir, key: "googleapis-root"},
+			"discovery":    {path: discoveryDir, key: "discovery-root"},
+			"showcase":     {path: showcaseDir, key: "showcase-root"},
+			"protobuf-src": {path: path.Join(protobufRootDir, protobufSubDir), key: "protobuf-src-root"},
+			"conformance":  {path: conformanceDir, key: "conformance-root"},
 		}
 		for _, root := range library.Roots {
 			if r, ok := rootMap[root]; ok && r.path != "" {
-				source[r.keys[0]] = r.path
-				if len(r.keys) > 1 {
-					source[r.keys[1]] = r.subdir
-				}
+				source[r.key] = r.path
 			}
 		}
 	}

internal/librarian/internal/rust/codec_test.go

@@ -32,6 +32,7 @@ func TestToSidekickConfig(t *testing.T) {
 		protobufDir    string
 		conformanceDir string
 		showcaseDir    string
+		protobufSubDir string
 		want           *sidekickconfig.Config
 	}{
 		{
@@ -598,6 +599,7 @@ func TestToSidekickConfig(t *testing.T) {
 			googleapisDir:  "/tmp/googleapis",
 			protobufDir:    "/tmp/protobuf",
 			conformanceDir: "/tmp/conformance",
+			protobufSubDir: "src",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -606,11 +608,10 @@ func TestToSidekickConfig(t *testing.T) {
 					SpecificationSource: "google/cloud/vision/v1",
 				},
 				Source: map[string]string{
-					"googleapis-root":     "/tmp/googleapis",
-					"protobuf-src-root":   "/tmp/protobuf",
-					"protobuf-src-subdir": "",
-					"conformance-root":    "/tmp/conformance",
-					"roots":               "googleapis,protobuf-src,conformance",
+					"googleapis-root":   "/tmp/googleapis",
+					"protobuf-src-root": "/tmp/protobuf/src",
+					"conformance-root":  "/tmp/conformance",
+					"roots":             "googleapis,protobuf-src,conformance",
 				},
 				Codec: map[string]string{
 					"package-name-override": "google-cloud-vision-v1",
@@ -646,7 +647,7 @@ func TestToSidekickConfig(t *testing.T) {
 		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
-			got := toSidekickConfig(tt.library, tt.channel, tt.googleapisDir, tt.discoveryDir, tt.protobufDir, "", tt.conformanceDir, tt.showcaseDir)
+			got := toSidekickConfig(tt.library, tt.channel, tt.googleapisDir, tt.discoveryDir, tt.protobufDir, tt.protobufSubDir, tt.conformanceDir, tt.showcaseDir)
 			if diff := cmp.Diff(tt.want, got); diff != "" {
 				t.Errorf("mismatch (-want +got):\n%s", diff)
 			}