Re-shade zinc to avoid classpath collisions with annotation processor…

…s. (#5953)

### Problem

Zinc used to be shaded before the `1.x.y` upgrade (#4729), but shading was removed due to an overabundance of optimism. When testing the zinc upgrade internally, we experienced a classpath collision between an annotation processor and zinc (in guava, although zinc has many other dependencies that could cause issues).

### Solution

Shade zinc, and ensure that our annotation processor uses a very old guava in order to attempt to force collisions in future.

src/python/pants/backend/jvm/subsystems/zinc.py

@@ -49,13 +49,17 @@ def register_options(cls, register):
           Shader.exclude_package('scala', recursive=True),
           Shader.exclude_package('xsbt', recursive=True),
           Shader.exclude_package('xsbti', recursive=True),
+          # Unfortunately, is loaded reflectively by the compiler.
+          Shader.exclude_package('org.apache.logging.log4j', recursive=True),
         ]
 
       cls.register_jvm_tool(register,
                             Zinc.ZINC_COMPILER_TOOL_NAME,
                             classpath=[
                               JarDependency('org.pantsbuild', 'zinc-compiler_2.11', '0.0.5'),
-                            ])
+                            ],
+                            main=Zinc.ZINC_COMPILE_MAIN,
+                            custom_rules=shader_rules)
 
       cls.register_jvm_tool(register,
                             'compiler-bridge',
@@ -85,7 +89,7 @@ def register_options(cls, register):
 
     @classmethod
     def _zinc(cls, products):
-      return cls.tool_classpath_from_products(products, Zinc.ZINC_COMPILER_TOOL_NAME, cls.options_scope)
+      return cls.tool_jar_from_products(products, Zinc.ZINC_COMPILER_TOOL_NAME, cls.options_scope)
 
     @classmethod
     def _compiler_bridge(cls, products):

src/python/pants/backend/jvm/tasks/jvm_compile/zinc/zinc_compile.py

@@ -268,7 +268,7 @@ def _zinc_cache_dir(self):
     than compiling it.
     """
     hasher = sha1()
-    for cp_entry in self._zinc.zinc + [self._zinc.compiler_interface, self._zinc.compiler_bridge]:
+    for cp_entry in [self._zinc.zinc, self._zinc.compiler_interface, self._zinc.compiler_bridge]:
       hasher.update(os.path.relpath(cp_entry, self.get_options().pants_workdir))
     key = hasher.hexdigest()[:12]
     return os.path.join(self.get_options().pants_bootstrapdir, 'zinc', key)
@@ -353,7 +353,7 @@ def compile(self, ctx, args, classpath, upstream_analysis,
         fp.write(arg)
         fp.write(b'\n')
 
-    if self.runjava(classpath=self._zinc.zinc,
+    if self.runjava(classpath=[self._zinc.zinc],
                     main=Zinc.ZINC_COMPILE_MAIN,
                     jvm_options=jvm_options,
                     args=zinc_args,

testprojects/3rdparty/com/google/guava/BUILD

@@ -0,0 +1,7 @@
+# NB: This is an intentionally ancient guava to attempt to flush out classpath collisions
+# with the compiler.
+jar_library(name='ancient-guava',
+            jars=[
+              jar('com.google.guava', 'guava', '10.0')
+            ])
+

testprojects/src/java/org/pantsbuild/testproject/annotation/processor/BUILD

@@ -7,7 +7,9 @@ annotation_processor(
   sources=globs('*.java'),
   processors=['org.pantsbuild.testproject.annotation.processor.ResourceMappingProcessor'],
   dependencies=[
-    '3rdparty:guava',
+    # NB: We use the oldest guava we can stomach here, in order to flush out classpath
+    # collisions between the compiler and annotation processors.
+    'testprojects/3rdparty/com/google/guava:ancient-guava',
   ],
 )
 

testprojects/src/java/org/pantsbuild/testproject/annotation/processor/ResourceMappingProcessor.java

@@ -4,7 +4,6 @@
 package org.pantsbuild.testproject.annotation.processor;
 
 import com.google.common.collect.ImmutableSet;
-import com.google.common.io.Closer;
 import java.io.Closeable;
 import java.io.IOException;
 import java.io.PrintWriter;
@@ -120,24 +119,25 @@ public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment
     }
 
     FileObject outputFile = createResourceOrDie("" /* no package */, REPORT_FILE_NAME);
-    Closer closer = Closer.create();
     try {
-      Set<String> typeNames = new HashSet<String>();
-      PrintWriter writer = closer.register(new PrintWriter(outputFile.openWriter()));
-      for (TypeElement annotation : annotations) {
-        Set<? extends Element> annotatedElements = roundEnv.getElementsAnnotatedWith(annotation);
-        Set<TypeElement> typeElements = ElementFilter.typesIn(annotatedElements);
-        for (TypeElement typeElement : typeElements) {
-          String typeName = elementUtils.getBinaryName(typeElement).toString();
-          typeNames.add(typeName);
-          writer.println(typeName);
+      PrintWriter writer = new PrintWriter(outputFile.openWriter());
+      try {
+        Set<String> typeNames = new HashSet<String>();
+        for (TypeElement annotation : annotations) {
+          Set<? extends Element> annotatedElements = roundEnv.getElementsAnnotatedWith(annotation);
+          Set<TypeElement> typeElements = ElementFilter.typesIn(annotatedElements);
+          for (TypeElement typeElement : typeElements) {
+            String typeName = elementUtils.getBinaryName(typeElement).toString();
+            typeNames.add(typeName);
+            writer.println(typeName);
+          }
         }
-      }
-
-      closer.close();
 
-      writeResourceMapping(typeNames, outputFile);
-      log(Diagnostic.Kind.NOTE, "Generated resource '%s'", outputFile.toUri());
+        writeResourceMapping(typeNames, outputFile);
+        log(Diagnostic.Kind.NOTE, "Generated resource '%s'", outputFile.toUri());
+      } finally {
+        writer.close();
+      }
     } catch (IOException e) {
       throw new RuntimeException(e);
     }