Resolve JAVA_HOME for source builds lazily (#1027)

With this commit we resolve JAVA_HOME lazily when attempting to build
Elasticsearch. When a source build is externally provided to Rally's
source artifact cache, there is no need to actually build it. However,
if the target system does not have any JDK installed and we attempt to
install Elasticsearch, the build subsystem is eagerly initialized
(despite the artifact being already cached) and is complaining that it
cannot find a JDK to build the artifact. By lazily resolving JAVA_HOME
we avoid that error.

esrally/mechanic/supplier.py

@@ -49,9 +49,14 @@ def create(cfg, sources, distribution, build, car, plugins=None):
     template_renderer = TemplateRenderer(version=es_version, os_name=target_os, arch=target_arch)
 
     if build_needed:
-        java_home = _java_home(car)
+        raw_build_jdk = car.mandatory_var("build.jdk")
+        try:
+            build_jdk = int(raw_build_jdk)
+        except ValueError:
+            raise exceptions.SystemSetupError(f"Car config key [build.jdk] is invalid: [{raw_build_jdk}] (must be int)")
+
         es_src_dir = os.path.join(_src_dir(cfg), _config_value(src_config, "elasticsearch.src.subdir"))
-        builder = Builder(es_src_dir, java_home, paths.logs())
+        builder = Builder(es_src_dir, build_jdk, paths.logs())
     else:
         builder = None
 
@@ -131,15 +136,6 @@ def create(cfg, sources, distribution, build, car, plugins=None):
     return CompositeSupplier(suppliers)
 
 
-def _java_home(car):
-    build_jdk = car.mandatory_var("build.jdk")
-    try:
-        _, path = jvm.resolve_path(int(build_jdk))
-        return path
-    except ValueError:
-        raise exceptions.SystemSetupError("Car config key \"build.jdk\" is invalid: \"{}\" (must be int)".format(build_jdk))
-
-
 def _required_version(version):
     if not version or version.strip() == "":
         raise exceptions.SystemSetupError("Could not determine version. Please specify the Elasticsearch distribution "
@@ -654,12 +650,19 @@ class Builder:
     It is not intended to be used directly but should be triggered by its mechanic.
     """
 
-    def __init__(self, src_dir, java_home=None, log_dir=None):
+    def __init__(self, src_dir, build_jdk=None, log_dir=None):
         self.src_dir = src_dir
-        self.java_home = java_home
+        self.build_jdk = build_jdk
+        self._java_home = None
         self.log_dir = log_dir
         self.logger = logging.getLogger(__name__)
 
+    @property
+    def java_home(self):
+        if not self._java_home:
+            _, self._java_home = jvm.resolve_path(self.build_jdk)
+        return self._java_home
+
     def build(self, commands, override_src_dir=None):
         for command in commands:
             self.run(command, override_src_dir)

tests/mechanic/supplier_test.py

@@ -134,12 +134,12 @@ def test_is_not_commit_hash(self):
 
 class BuilderTests(TestCase):
     @mock.patch("esrally.utils.process.run_subprocess")
-    @mock.patch("esrally.utils.jvm.major_version")
-    def test_build_on_jdk_8(self, jvm_major_version, mock_run_subprocess):
-        jvm_major_version.return_value = 8
+    @mock.patch("esrally.utils.jvm.resolve_path")
+    def test_build_on_jdk_8(self, jvm_resolve_path, mock_run_subprocess):
+        jvm_resolve_path.return_value = (8, "/opt/jdk8")
         mock_run_subprocess.return_value = False
 
-        b = supplier.Builder(src_dir="/src", java_home="/opt/jdk8", log_dir="logs")
+        b = supplier.Builder(src_dir="/src", build_jdk=8, log_dir="logs")
         b.build(["./gradlew clean", "./gradlew assemble"])
 
         calls = [
@@ -152,12 +152,12 @@ def test_build_on_jdk_8(self, jvm_major_version, mock_run_subprocess):
         mock_run_subprocess.assert_has_calls(calls)
 
     @mock.patch("esrally.utils.process.run_subprocess")
-    @mock.patch("esrally.utils.jvm.major_version")
-    def test_build_on_jdk_10(self, jvm_major_version, mock_run_subprocess):
-        jvm_major_version.return_value = 10
+    @mock.patch("esrally.utils.jvm.resolve_path")
+    def test_build_on_jdk_10(self, jvm_resolve_path, mock_run_subprocess):
+        jvm_resolve_path.return_value = (10, "/opt/jdk10")
         mock_run_subprocess.return_value = False
 
-        b = supplier.Builder(src_dir="/src", java_home="/opt/jdk10", log_dir="logs")
+        b = supplier.Builder(src_dir="/src", build_jdk=8, log_dir="logs")
         b.build(["./gradlew clean", "./gradlew assemble"])
 
         calls = [