Allow ~/home in downloaderConfig of RepositoryOptions

Similar to `--distdir` it makes sense to provide a `--experimental_downloader_config` from `~/.bazelrc` where it is more convenient to address a file in ones home directory by using `~/...` syntax instead of on absolute path.

Closes #24618.

PiperOrigin-RevId: 708007102
Change-Id: Ia8d0ebc1cb79c95ea58888c08746adc917d3fb63

src/main/java/com/google/devtools/build/lib/bazel/repository/RepositoryOptions.java

@@ -207,14 +207,15 @@ public class RepositoryOptions extends OptionsBase {
       defaultValue = "null",
       documentationCategory = OptionDocumentationCategory.REMOTE,
       effectTags = {OptionEffectTag.UNKNOWN},
+      converter = OptionsUtils.PathFragmentConverter.class,
       help =
           "Specify a file to configure the remote downloader with. This file consists of lines, "
               + "each of which starts with a directive (`allow`, `block` or `rewrite`) followed "
               + "by either a host name (for `allow` and `block`) or two patterns, one to match "
               + "against, and one to use as a substitute URL, with back-references starting from "
               + "`$1`. It is possible for multiple `rewrite` directives for the same URL to be "
               + "give, and in this case multiple URLs will be returned.")
-  public String downloaderConfig;
+  public PathFragment downloaderConfig;
 
   /** See {@link #workerForRepoFetching}. */
   public enum WorkerForRepoFetching {

src/main/java/com/google/devtools/build/lib/bazel/repository/downloader/UrlRewriter.java

@@ -21,7 +21,6 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Ascii;
 import com.google.common.base.Preconditions;
-import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
@@ -32,6 +31,7 @@
 import com.google.devtools.build.lib.events.Reporter;
 import com.google.devtools.build.lib.util.OS;
 import com.google.devtools.build.lib.vfs.Path;
+import com.google.devtools.build.lib.vfs.PathFragment;
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
@@ -86,11 +86,12 @@ public class UrlRewriter {
    * @param reporter Used for logging when URLs are rewritten.
    */
   public static UrlRewriter getDownloaderUrlRewriter(
-      Path workspaceRoot, String configPath, Reporter reporter) throws UrlRewriterParseException {
+      Path workspaceRoot, @Nullable PathFragment configPath, Reporter reporter)
+      throws UrlRewriterParseException {
     Consumer<String> log = str -> reporter.handle(Event.info(str));
 
     // "empty" UrlRewriter shouldn't alter auth headers
-    if (Strings.isNullOrEmpty(configPath)) {
+    if (configPath == null || configPath.isEmpty()) {
       return new UrlRewriter(log, "", new StringReader(""));
     }
 
@@ -101,13 +102,13 @@ public static UrlRewriter getDownloaderUrlRewriter(
 
     if (!actualConfigPath.exists()) {
       throw new UrlRewriterParseException(
-          String.format("Unable to find downloader config file %s", configPath));
+          String.format("Unable to find downloader config file %s", configPath.getPathString()));
     }
 
     try (InputStream inputStream = actualConfigPath.getInputStream();
         Reader inputStreamReader = new InputStreamReader(inputStream);
         Reader reader = new BufferedReader(inputStreamReader)) {
-      return new UrlRewriter(log, configPath, reader);
+      return new UrlRewriter(log, configPath.getPathString(), reader);
     } catch (IOException e) {
       throw new UrlRewriterParseException(e.getMessage());
     }