Buck: No system compiler found, Did you install the JRE instead of the JDK?

[zoom2manoj]

I'm trying to build sample demo using as below command on Window system,

From the rootcross-platform-scale-2015-demo/directory demo_app_android is an alias in .buckconfig for //android:demo-app. Either works. buck build demo_app_android

but I'm getting issue as below :

`Not using buckd because watchman isn't installed.
[-] PARSING BUCK FILES...FINISHED 0.0s [100%]
BUILD FAILED: //android:demo-app#compile_uber_r_dot_java failed on step javac wi
th an exception:
No system compiler found. Did you install the JRE instead of the JDK?
com.facebook.buck.util.HumanReadableException: No system compiler found. Did you
install the JRE instead of the JDK?
at com.facebook.buck.jvm.java.JdkProvidedInMemoryJavac.createCompiler(Jd
kProvidedInMemoryJavac.java:63)
at com.facebook.buck.jvm.java.Jsr199Javac.buildWithClasspath(Jsr199Javac
.java:124)
at com.facebook.buck.jvm.java.JavacStep.performBuild(JavacStep.java:200)

    at com.facebook.buck.jvm.java.JavacStep.tryBuildWithFirstOrderDeps(Javac

Step.java:190)
at com.facebook.buck.jvm.java.JavacStep.execute(JavacStep.java:151)
at com.facebook.buck.step.DefaultStepRunner.runStepForBuildTarget(Defaul
tStepRunner.java:47)
at com.facebook.buck.rules.CachingBuildEngine.executeCommandsNowThatDeps
AreBuilt(CachingBuildEngine.java:1387)
at com.facebook.buck.rules.CachingBuildEngine.lambda$11(CachingBuildEngi
ne.java:339)
at com.facebook.buck.util.concurrent.WeightedListeningExecutorService.la
mbda$0(WeightedListeningExecutorService.java:77)
at com.google.common.util.concurrent.Futures$AsyncChainingFuture.doTrans
form(Futures.java:1442)
at com.google.common.util.concurrent.Futures$AsyncChainingFuture.doTrans
form(Futures.java:1433)
at com.google.common.util.concurrent.Futures$AbstractChainingFuture.run(
Futures.java:1408)
at com.google.common.util.concurrent.Futures$2$1.run(Futures.java:1177)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

[-] BUILDING...FINISHED 0.5s [100%]`

Can anyone suggest me what I'm doing wrong in these steps according to https://buckbuild.com/setup/getting_started.html

[xzstar]

The reason is System.getProperty("java.home") points to a jre directory.
Workaround: copy your jdk/lib/tools.jar to jre/lib/tools

[seanpoulter]

We should add solution(s) for this to the Getting Started and/or Troubleshooting docs and incude the link in the error message. This is as much of a problem of setting up your PATH as copying files, and since it's part of the build environment setup it'll probably cause problems for a few folks.

FWIW, here's my process to diagnose the problem and fix it by updating the PATH before I build.

1. getSystemJavaCompiler() must be null to get the error message:

```.java
// file: Reproduce.java
import javax.tools.ToolProvider;
import javax.tools.JavaCompiler;

public class Reproduce {
    public static void main(String[] args) {
        String home = System.getProperty("java.home");
        System.out.printf("java.home:\t%s\n", home);

        JavaCompiler c = ToolProvider.getSystemJavaCompiler();
        System.out.printf("JavaCompiler:\t%s\n", c);
    }
}
```

```.bat
> javac Reproduce.java
> java Reproduce
java.home:  C:\Program Files (x86)\Java\jre1.8.0_151
JavaCompiler:   null
```

1. Should this be using JAVA_HOME?

   > set java_
   JAVA_HOME=c:\Program Files (x86)\Java\jdk1.8.0_151
   JAVA_JDK_BIN=C:\Program Files (x86)\Java\jdk1.8.0_151\bin
   

   Doesn't look like it.
   The docs say "java.home" is the JRE installation directory.

2. Which java is being used?
   ```.bat

   where java
   C:\ProgramData\Oracle\Java\javapath\java.exe
   C:\Program Files (x86)\Java\jdk1.8.0_151\bin\java.exe
   ```

3. There's an unresolved bug to improve the getSystemJavaCompiler() docs to say it must be called with the JDK not the JRE.

4. Does it work if we use java from the JDK instead of the JRE?

   ```.bat

   set PATH=%JAVA_JDK_BIN%;%PATH%
   where java
   C:\Program Files (x86)\Java\jdk1.8.0_151\binjava.exe
   C:\ProgramData\Oracle\Javajavapathjava.exe

   java Reproduce
   java.home: C:\Program Files (x86)\Java\jdk1.8.0_151\jre
   JavaCompiler: com.sun.tools.javac.api.JavacTool@17327b6
   ```

   Bingo.