Compiling with System.getProperty can throw NPE rather than useful error

[niloc132]

GWT version: 2.9, 2.10, 2.11
Browser (with version): n/a
Operating System: any

---

Description

Both binding properties and configuration properties (single value only) can be used to provide strings that can be read at compile time via System.getProperty, but if no value is set on a configuration property, a NPE will occur in the compiler.

Cases that should be supported:

• Multi-value configuration properties correctly emit an error:

     [ERROR] Errors in 'com/google/gwt/dev/jjs/test/SystemGetPropertyTest.java'
        [ERROR] Line 42: Property 'someConfigProperty' is multivalued. Multivalued properties are not supported by System.getProperty().
  

• No property defined in .gwt.xml, either binding or configuration results in default value being used (if provided), otherwise error:

     [ERROR] Errors in 'com/google/gwt/dev/jjs/test/SystemGetPropertyTest.java'
        [ERROR] Line 45: Property 'unknownProperty' is not defined.
  

• Configuration properties defined without a value however result in an NPE:

     Compiling 1 permutation
        [ERROR] An internal compiler exception occurred
  com.google.gwt.dev.jjs.InternalCompilerException: Unexpected error during visit.
      at com.google.gwt.dev.jjs.ast.JVisitor.translateException(JVisitor.java:111)
      at com.google.gwt.dev.jjs.ast.JModVisitor.acceptImmutable(JModVisitor.java:313)
      at com.google.gwt.dev.jjs.ast.JMethodCall.visitChildren(JMethodCall.java:275)
      at com.google.gwt.dev.jjs.ast.JMethodCall.traverse(JMethodCall.java:266)
      at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:273)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:265)
      at com.google.gwt.dev.jjs.ast.JVisitor.accept(JVisitor.java:118)
      at com.google.gwt.dev.jjs.ast.JExpressionStatement.traverse(JExpressionStatement.java:42)
      at com.google.gwt.dev.jjs.ast.JModVisitor$ListContext.traverse(JModVisitor.java:88)
      at com.google.gwt.dev.jjs.ast.JModVisitor.acceptWithInsertRemove(JModVisitor.java:331)
      at com.google.gwt.dev.jjs.ast.JBlock.traverse(JBlock.java:94)
      at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:273)
      at com.google.gwt.dev.jjs.ast.JVisitor.accept(JVisitor.java:139)
      at com.google.gwt.dev.jjs.ast.JVisitor.accept(JVisitor.java:135)
      at com.google.gwt.dev.jjs.ast.JMethodBody.traverse(JMethodBody.java:83)
      at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:273)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:265)
      at com.google.gwt.dev.jjs.ast.JMethod.visitChildren(JMethod.java:786)
      at com.google.gwt.dev.jjs.ast.JMethod.traverse(JMethod.java:778)
      at com.google.gwt.dev.jjs.ast.JModVisitor$ListContextImmutable.traverse(JModVisitor.java:169)
      at com.google.gwt.dev.jjs.ast.JModVisitor.acceptWithInsertRemoveImmutable(JModVisitor.java:336)
      at com.google.gwt.dev.jjs.ast.JClassType.traverse(JClassType.java:147)
      at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:273)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:265)
      at com.google.gwt.dev.jjs.ast.JProgram.visitModuleTypes(JProgram.java:1284)
      at com.google.gwt.dev.jjs.ast.JProgram.traverse(JProgram.java:1249)
      at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:273)
      at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:265)
      at com.google.gwt.dev.jjs.impl.ResolvePermutationDependentValues.execImpl(ResolvePermutationDependentValues.java:163)
      at com.google.gwt.dev.jjs.impl.ResolvePermutationDependentValues.exec(ResolvePermutationDependentValues.java:113)
      at com.google.gwt.dev.jjs.JavaToJavaScriptCompiler.compilePermutation(JavaToJavaScriptCompiler.java:333)
      at com.google.gwt.dev.jjs.JavaToJavaScriptCompiler.compilePermutation(JavaToJavaScriptCompiler.java:272)
      at com.google.gwt.dev.CompilePerms.compile(CompilePerms.java:198)
      at com.google.gwt.dev.ThreadedPermutationWorkerFactory$ThreadedPermutationWorker.compile(ThreadedPermutationWorkerFactory.java:50)
      at com.google.gwt.dev.PermutationWorkerFactory$Manager$WorkerThread.run(PermutationWorkerFactory.java:74)
      at java.base/java.lang.Thread.run(Thread.java:829)
  Caused by: java.lang.NullPointerException
      at com.google.gwt.thirdparty.guava.common.base.Preconditions.checkNotNull(Preconditions.java:212)
      at com.google.gwt.thirdparty.guava.common.base.Joiner.toString(Joiner.java:447)
      at com.google.gwt.thirdparty.guava.common.base.Joiner.appendTo(Joiner.java:110)
      at com.google.gwt.thirdparty.guava.common.base.Joiner.appendTo(Joiner.java:154)
      at com.google.gwt.thirdparty.guava.common.base.Joiner.join(Joiner.java:197)
      at com.google.gwt.thirdparty.guava.common.base.Joiner.join(Joiner.java:186)
      at com.google.gwt.dev.jjs.impl.ResolvePermutationDependentValues$ValueReplacer.propertyValueExpression(ResolvePermutationDependentValues.java:79)
      at com.google.gwt.dev.jjs.impl.ResolvePermutationDependentValues$ValueReplacer.endVisit(ResolvePermutationDependentValues.java:73)
      at com.google.gwt.dev.jjs.ast.JPermutationDependentValue.traverse(JPermutationDependentValue.java:112)
      at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)
      at com.google.gwt.dev.jjs.ast.JModVisitor.acceptImmutable(JModVisitor.java:305)
      ... 39 more
           [ERROR] at SystemGetPropertyTest.java(44): System.getProperty("someConfigPropertyUnset", "bar")
           [ERROR] at SystemGetPropertyTest.java(44): Assert.assertEquals("bar", System.getProperty("someConfigPropertyUnset", "bar"))
           [ERROR] at SystemGetPropertyTest.java(44): Assert.assertEquals("bar", System.getProperty("someConfigPropertyUnset", "bar"))
           [ERROR] at SystemGetPropertyTest.java(41): {
    Assert.assertEquals("foo", "foo");
    Assert.assertEquals("foo", "foo");
    Assert.assertEquals("bar", System.getProperty("someConfigPropertyUnset", "bar"));
  }
           [ERROR] at SystemGetPropertyTest.java(41): {
    Assert.assertEquals("foo", "foo");
    Assert.assertEquals("foo", "foo");
    Assert.assertEquals("bar", System.getProperty("someConfigPropertyUnset", "bar"));
  }
           [ERROR] at SystemGetPropertyTest.java(41): com.google.gwt.dev.jjs.test.SystemGetPropertyTest.testConfigurationProperties()V
           [ERROR] at SystemGetPropertyTest.java(23): com.google.gwt.dev.jjs.test.SystemGetPropertyTest (extends GWTTestCase)
           [ERROR] at Unknown(0): <JProgram>
        [ERROR] Unrecoverable exception, shutting down
  

Steps to reproduce

Declare a configuration property, but don't assign it (for example, one .gwt.xml for a library might declare it, and a downstream app may choose to set it):

  <define-configuration-property name="someConfigPropertyUnset" is-multi-valued="false"/>

Attempt to use that property in GWT/Java sources without a default:

    assertEquals("bar", System.getProperty("someConfigPropertyUnset", "bar"));

Expected: default value is used
Actual: NPE is thrown during compilation

Known workarounds

The simplest workaround is to just define a "this is unset" value for the configuration property, but that means that shared code has two places to change the default.

  <set-configuration-property name="someConfigPropertyUnset" value="this-is-unset" />

[niloc132]

Also related to #9806 and #9807 I believe.