bazel_0_4: add optional Nix-specific hacks

* Skip verifying checksums for already fetched packages.
  Needed for two-staged building in Nix:
    1. Build a fixed derivation with `bazel fetch` (filtered out of non-reproducable bits).
    2. Build an actual derivation which uses fetched dependencies (skipping
       checksums needed here because they depend on the build directory).
* Don't clean environment variables for children processes.
  Needed for Nix compiler wrappers.

pkgs/development/tools/build-managers/bazel/0.4.nix

@@ -1,4 +1,8 @@
-{ stdenv, fetchurl, jdk, zip, unzip, bash, makeWrapper, which }:
+{ stdenv, lib, fetchurl, jdk, zip, unzip, bash, makeWrapper, which
+# Always assume all markers valid (don't redownload dependencies).
+# Also, don't clean up environment variables.
+, enableNixHacks ? false
+}:
 
 stdenv.mkDerivation rec {
 
@@ -21,6 +25,8 @@ stdenv.mkDerivation rec {
 
   sourceRoot = ".";
 
+  patches = lib.optional enableNixHacks ./nix-hacks.patch;
+
   postPatch = ''
     for f in $(grep -l -r '#!/bin/bash'); do
       substituteInPlace "$f" --replace '#!/bin/bash' '#!${bash}/bin/bash'

pkgs/development/tools/build-managers/bazel/nix-hacks.patch

@@ -0,0 +1,51 @@
+diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryDelegatorFunction.java b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryDelegatorFunction.java
+index eafa09fb5..d2d5e40e8 100644
+--- a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryDelegatorFunction.java
++++ b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryDelegatorFunction.java
+@@ -287,21 +287,8 @@ public final class RepositoryDelegatorFunction implements SkyFunction {
+           markerData.put(key, value);
+         }
+       }
+-      boolean result = false;
+-      if (markerRuleKey.equals(ruleKey)) {
+-        result = handler.verifyMarkerData(rule, markerData, env);
+-        if (env.valuesMissing()) {
+-          return null;
+-        }
+-      }
+ 
+-      if (result) {
+-        return new Fingerprint().addString(content).digestAndReset();
+-      } else {
+-        // So that we are in a consistent state if something happens while fetching the repository
+-        markerPath.delete();
+-        return null;
+-      }
++      return new Fingerprint().addString(content).digestAndReset();
+ 
+     } catch (IOException e) {
+       throw new RepositoryFunctionException(e, Transience.TRANSIENT);
+diff --git a/src/main/java/com/google/devtools/build/lib/shell/JavaSubprocessFactory.java b/src/main/java/com/google/devtools/build/lib/shell/JavaSubprocessFactory.java
+index a7ebc8f7a..40f2049fa 100644
+--- a/src/main/java/com/google/devtools/build/lib/shell/JavaSubprocessFactory.java
++++ b/src/main/java/com/google/devtools/build/lib/shell/JavaSubprocessFactory.java
+@@ -129,7 +129,6 @@ public class JavaSubprocessFactory implements SubprocessFactory {
+     ProcessBuilder builder = new ProcessBuilder();
+     builder.command(params.getArgv());
+     if (params.getEnv() != null) {
+-      builder.environment().clear();
+       builder.environment().putAll(params.getEnv());
+     }
+ 
+diff --git a/src/main/java/com/google/devtools/build/lib/worker/Worker.java b/src/main/java/com/google/devtools/build/lib/worker/Worker.java
+index 0268d1b2b..637364657 100644
+--- a/src/main/java/com/google/devtools/build/lib/worker/Worker.java
++++ b/src/main/java/com/google/devtools/build/lib/worker/Worker.java
+@@ -77,7 +77,6 @@ class Worker {
+         new ProcessBuilder(command)
+             .directory(workDir.getPathFile())
+             .redirectError(Redirect.appendTo(logFile.getPathFile()));
+-    processBuilder.environment().clear();
+     processBuilder.environment().putAll(workerKey.getEnv());
+ 
+     this.process = processBuilder.start();