FULL PRODUCT VERSION :
openjdk version "9-Ubuntu"
OpenJDK Runtime Environment (build 9-Ubuntu+0-9b181-4)
OpenJDK 64-Bit Server VM (build 9-Ubuntu+0-9b181-4, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux astoria 4.10.0-32-generic #36-Ubuntu SMP Tue Aug 8 12:10:06 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
javadoc has started validating source files that it shouldn't be reading. If these are invalid, then javadoc crashes with an exception. This is unexpected, and a regression from Java 8.

With source files in a layout like the following, where "Valid" is a valid Java source file, and "Invalid.java" is an invalid Java source file:

com/example/Valid.java
com/example/Invalid.java

... running "javadoc com/example/Valid.java" used to succeed, but now fails with a big exception, starting with:

javadoc: error - An exception occurred while building a component: Contents
(com.sun.tools.javac.code.ClassFinder$BadClassFile: bad source file: ./com/example/Invalid.java
  file does not contain class com.example.Invalid


This happens when people litter test or example code around, e.g. Invalid.java contains:

/* no package line */
class Invalid {}


REGRESSION. Last worked in version 8u131

ADDITIONAL REGRESSION INFORMATION:
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-2ubuntu1.16.04.3-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
# This bash script creates some source files:

mkdir -p a

# first, a valid class:
echo 'package a; public class B {}' > a/B.java

# then, an invalid one:
echo '/* no package */ class RealClassName {}' > a/RealFileName.java

# and tries to generate the javadoc for just the valid class:
javadoc a/B.java


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
On Java 8, the invalid files are ignored; the doc is generated for just "B".

ACTUAL -
On Java 9, javadoc fails, and the big exception is output.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
javadoc: error - An exception occurred while building a component: Contents
(com.sun.tools.javac.code.ClassFinder$BadClassFile: bad source file: ./a/C.java
  file does not contain class a.C
  Please remove or make sure it appears in the correct subdirectory of the sourcepath.)
Please file a bug against the javadoc tool via the Java bug reporting page
(http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com)
for duplicates. Include error messages and the following diagnostic in your report. Thank you.
com.sun.tools.javac.code.ClassFinder$BadClassFile: bad source file: ./a/C.java
  file does not contain class a.C
  Please remove or make sure it appears in the correct subdirectory of the sourcepath.
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.readSourceFile(JavaCompiler.java:856)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.readSourceFile(JavaCompiler.java:783)
at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.lambda$new$0(JavaCompiler.java:343)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.fillIn(ClassFinder.java:352)
at jdk.compiler/com.sun.tools.javac.code.ClassFinder.complete(ClassFinder.java:285)
at jdk.compiler/com.sun.tools.javac.code.Symbol.complete(Symbol.java:633)
at jdk.compiler/com.sun.tools.javac.code.Symbol$ClassSymbol.complete(Symbol.java:1314)
at jdk.compiler/com.sun.tools.javac.code.Symbol$ClassSymbol.flags(Symbol.java:1248)
at jdk.compiler/com.sun.tools.javac.code.Symbol$TypeSymbol.getEnclosedElements(Symbol.java:800)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getItems0(Utils.java:2468)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getItems0(Utils.java:2463)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.recursiveGetItems(Utils.java:2451)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils$16.visitPackage(Utils.java:2436)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils$16.visitPackage(Utils.java:2432)
at jdk.compiler/com.sun.tools.javac.code.Symbol$PackageSymbol.accept(Symbol.java:1166)
at java.compiler@9-Ubuntu/javax.lang.model.util.AbstractElementVisitor6.visit(AbstractElementVisitor6.java:106)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getItems(Utils.java:2445)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getClasses(Utils.java:2182)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.util.Utils.getAllClasses(Utils.java:2355)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.ConstantsSummaryBuilder.hasConstantField(ConstantsSummaryBuilder.java:258)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.ConstantsSummaryBuilder.buildContents(ConstantsSummaryBuilder.java:171)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.AbstractBuilder.build(AbstractBuilder.java:157)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.AbstractBuilder.buildChildren(AbstractBuilder.java:200)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.ConstantsSummaryBuilder.buildConstantSummary(ConstantsSummaryBuilder.java:156)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.AbstractBuilder.build(AbstractBuilder.java:157)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.builders.ConstantsSummaryBuilder.build(ConstantsSummaryBuilder.java:136)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.generateOtherFiles(AbstractDoclet.java:228)
at jdk.javadoc/jdk.javadoc.internal.doclets.formats.html.HtmlDoclet.generateOtherFiles(HtmlDoclet.java:116)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.startGeneration(AbstractDoclet.java:213)
at jdk.javadoc/jdk.javadoc.internal.doclets.toolkit.AbstractDoclet.run(AbstractDoclet.java:117)
at jdk.javadoc/jdk.javadoc.doclet.StandardDoclet.run(StandardDoclet.java:72)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.parseAndExecute(Start.java:574)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:423)
at jdk.javadoc/jdk.javadoc.internal.tool.Start.begin(Start.java:340)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.execute(Main.java:63)
at jdk.javadoc/jdk.javadoc.internal.tool.Main.main(Main.java:52)
1 error


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
See "steps to reproduce".
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Teach the build system to remove the example classes from the source tree before building?