Bug 1666032: ensure java from PATH == java from JDK_BIN_DIR r=rstewart

In the build process, there's two ways that java is used:
* From the path
* From the java-bin-path specified in the mozconfig

Before, to assert that both "java" usages would be consistent, the
implementation assumed that there was only a single "java" binary
per-JDK-version, and all duplicate "binaries" were symlinks to the
original.

However, in Fedora, it has two identical full binaries: one in
$JDK/bin, and one in $JDK/jre/bin. The symlink theory was incorrect.

So instead, we can assert that both "java" usages are consistent
by checking their versions and asserting that they are equivalent.

Differential Revision: https://phabricator.services.mozilla.com/D90918

python/mozboot/mozboot/base.py

@@ -858,13 +858,22 @@ class BaseBootstrapper(object):
 
             if jarsigner and java:
                 jdk_bin_dir = os.path.dirname(os.path.realpath(jarsigner))
-                if (os.path.realpath(java) !=
-                    os.path.realpath(which('java', path=jdk_bin_dir))):
+                jdk_bin_java = which('java', path=jdk_bin_dir)
+
+                # Different parts of the build process reference "java" differently.
+                # In bootstrap, we run some Android tooling which uses "java" from the PATH.
+                # Meanwhile, in build, we'll use the "java" found in the --with-java-bin-path.
+                # To ensure we don't run into surprises, we check that both of our "java"s are
+                # from the same JDK version.
+                path_java_version = _resolve_java_version(java)[0]
+                jdk_bin_version = _resolve_java_version(jdk_bin_java)[0]
+                if path_java_version != jdk_bin_version:
                     # This can happen on Ubuntu if "update-alternatives" has been
-                    # manually overridden once for either "java" or "jarsigner".
-                    raise Exception('The "java" and "jarsigner" binaries on the PATH are '
-                                    'currently coming from two different JDKs. Please '
-                                    'resolve this, or explicitly set JAVA_HOME.')
+                    # manually overridden for either "java" or "jarsigner".
+                    raise Exception('The "java" (JDK {}) and "jarsigner" (JDK {}) binaries on the '
+                                    'PATH are currently coming from two different JDKs. Please '
+                                    'resolve this, or explicitly set JAVA_HOME.'
+                                    .format(path_java_version, jdk_bin_version))
 
         if not jdk_bin_dir:
             raise Exception('You need to have Java Development Kit version 1.8 installed. '
@@ -872,7 +881,29 @@ class BaseBootstrapper(object):
 
         java = which('java', path=jdk_bin_dir)
         try:
-            output = subprocess.check_output([java,
+            version, output = _resolve_java_version(java)
+
+            if not version or version not in ['1.8', '8']:
+                raise Exception('You need to have Java Development Kit version '
+                                '1.8 installed (found {} but could not parse '
+                                'version "{}"). Check the JAVA_HOME environment '
+                                'variable. Please install JDK 1.8 from '
+                                'https://adoptopenjdk.net/?variant=openjdk8.'
+                                .format(java, output))
+
+            mozconfig_builder.append('''
+            # Use the same Java binary that was used in bootstrap in case the global
+            # system default version is changed.
+            ac_add_options --with-java-bin-path={}
+            '''.format(jdk_bin_dir))
+        except subprocess.CalledProcessError as e:
+            raise Exception('Failed to get java version from {}: {}'.format(java, e.output))
+
+        print('Your version of Java ({}) is at least 1.8 ({}).'.format(java, version))
+
+
+def _resolve_java_version(java_path):
+    output = subprocess.check_output([java_path,
                                       '-XshowSettings:properties',
                                       '-version'],
                                      stderr=subprocess.STDOUT,
@@ -886,26 +917,8 @@ class BaseBootstrapper(object):
     version = [line for line in output.splitlines()
                if 'java.specification.version' in line]
 
-            unknown_version_exception = Exception('You need to have Java Development Kit version '
-                                                  '1.8 installed (found {} but could not parse '
-                                                  'version "{}"). Check the JAVA_HOME environment '
-                                                  'variable. Please install JDK 1.8 from '
-                                                  'https://adoptopenjdk.net/?variant=openjdk8.'
-                                                  .format(java, output))
-
-            if not len(version) == 1:
-                raise unknown_version_exception
+    if len(version) != 1:
+        return None, output
 
     version = version[0].split(' = ')[-1]
-            if version not in ['1.8', '8']:
-                raise unknown_version_exception
-
-            mozconfig_builder.append('''
-            # Use the same Java binary that was used in bootstrap in case the global
-            # system default version is changed.
-            ac_add_options --with-java-bin-path={}
-            '''.format(jdk_bin_dir))
-        except subprocess.CalledProcessError as e:
-            raise Exception('Failed to get java version from {}: {}'.format(java, e.output))
-
-        print('Your version of Java ({}) is at least 1.8 ({}).'.format(java, version))
+    return version, output