gazelle: Resolve the Runfiles library (#243)

Author: illicitonion

java/gazelle/resolve.go

@@ -199,6 +199,16 @@ func (jr *Resolver) resolveSinglePackage(c *config.Config, pc *javaconfig.Config
 		return label.NoLabel, nil
 	}
 
+	// As per https://github.com/bazelbuild/bazel/blob/347407a88fd480fc5e0fbd42cc8196e4356a690b/tools/java/runfiles/Runfiles.java#L41
+	if imp.Name == "com.google.devtools.build.runfiles" {
+		runfilesLabel := "@bazel_tools//tools/java/runfiles"
+		l, err := label.Parse(runfilesLabel)
+		if err != nil {
+			return label.NoLabel, fmt.Errorf("failed to parse known-good runfiles label %s: %w", runfilesLabel, err)
+		}
+		return l, nil
+	}
+
 	if l, err := jr.lang.mavenResolver.Resolve(imp, pc.ExcludedArtifacts(), pc.MavenRepositoryName()); err != nil {
 		var noExternal *maven.NoExternalImportsError
 		var multipleExternal *maven.MultipleExternalImportsError

java/gazelle/testdata/runfiles/WORKSPACE

@@ -0,0 +1 @@
+workspace(name = "runfiles_example")

java/gazelle/testdata/runfiles/expectedStderr.txt

@@ -0,0 +1 @@
+{"level":"warn","_c":"maven-resolver","error":"open %WORKSPACEPATH%/maven_install.json: no such file or directory","message":"not loading maven dependencies"}

java/gazelle/testdata/runfiles/src/main/java/com/example/hello/BUILD.out

@@ -0,0 +1,8 @@
+load("@rules_java//java:defs.bzl", "java_library")
+
+java_library(
+    name = "hello",
+    srcs = ["Hello.java"],
+    visibility = ["//:__subpackages__"],
+    deps = ["@bazel_tools//tools/java/runfiles"],
+)

java/gazelle/testdata/runfiles/src/main/java/com/example/hello/Hello.java

@@ -0,0 +1,22 @@
+package com.example.hello;
+
+import com.google.devtools.build.runfiles.AutoBazelRepository;
+import com.google.devtools.build.runfiles.Runfiles;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+@AutoBazelRepository
+public class Hello {
+    public static String sayHi() throws IOException {
+        Runfiles.Preloaded runfiles = Runfiles.preload();
+        String path = runfiles
+                .withSourceRepository(AutoBazelRepository_Hello.NAME)
+                .rlocation("runfiles_example/src/main/java/com/example/hello/data.txt");
+        String fileContents = Files.readString(Path.of(path), StandardCharsets.UTF_8);
+
+        return String.format("Hello %s", fileContents);
+    }
+}