bazel: Bazel throws exception if no local JDK is installed

It looks like this was caused by javabase refactorings in these versions, with two distinct breakages occurring in 0.18 -> 0.19 and 0.20 -> 0.21. Representative build logs from a build with Bazel 0.21:

$ bazel-0.21 build //src:bazel
[...]
ERROR: /Users/john/src/bazel/tools/jdk/BUILD:52:1: Executing genrule //tools/jdk:gen_include/darwin/jni_md.h failed (Exit 1) bash failed: error executing command /bin/bash -c 'source external/bazel_tools/tools/genrule/genrule-setup.sh; cp external/local_jdk/include/darwin/jni_md.h bazel-out/darwin-fastbuild/genfiles/tools/jdk/include/darwin/jni_md.h'

Use --sandbox_debug to see verbose messages from the sandbox
cp: external/local_jdk/include/darwin/jni_md.h: No such file or directory
Target //src:bazel failed to build

The genrule comes from a macro:

def java_runtime_files(name, srcs):
    """Copies the given sources out of the current Java runtime."""

    native.filegroup(
        name = name,
        srcs = srcs,
    )   
    for src in srcs:
        native.genrule(
            name = "gen_%s" % src,
            srcs = ["@bazel_tools//tools/jdk:current_java_runtime"],
            toolchains = ["@bazel_tools//tools/jdk:current_java_runtime"],
            cmd = "cp $(JAVABASE)/%s $@" % src, 
            outs = [src],
        )   

Editing that genrule to print out what files it sees indicates that $(JAVABASE) has become decoupled from $(locations @bazel_tools//tools/jdk:current_java_runtime).

• v0.18
  • $(JAVABASE) =external/local_jdk
  • genrule srcs has ./external/local_jdk/include/jni.h
• v0.19
  • $(JAVABASE) =external/local_jdk
  • genrule srcs has ./external/embedded_jdk/include/jni.h
• v0.20
  • $(JAVABASE) =external/local_jdk
  • genrule srcs has ./external/embedded_jdk/include/jni.h
• v0.21
  • $(JAVABASE) =external/local_jdk
  • genrule srcs has ./external/remotejdk_macos/include/jni.h