FULL PRODUCT VERSION :
java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin Lingchaos-iMac 17.0.0 Darwin Kernel Version 17.0.0: Thu Aug 24 21:48:19 PDT 2017; root:xnu-4570.1.46~2/RELEASE_X86_64 x86_64

A DESCRIPTION OF THE PROBLEM :
Jshell crashes when I use `TAB` to complete something in it.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
I can always reproduce this bug by these steps:

$ jshell -v --add-modules jdk.incubator.httpclient

jshell> import jdk.incubator.http.*;

jshell> HttpRequest.newBuilder().uri(new URI( // here type `TAB` twice

then jshell crashes with the traceback:

jshell> HttpRequest.newBuilder().uri(new URI(Exception in thread "main" java.lang.StringIndexOutOfBoundsException: index 1230,length 1230
at java.base/java.lang.String.checkIndex(String.java:3075)
at java.base/java.lang.AbstractStringBuilder.charAt(AbstractStringBuilder.java:281)
at java.base/java.lang.StringBuilder.charAt(StringBuilder.java:77)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter.reflow(JavadocFormatter.java:590)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter.access$200(JavadocFormatter.java:70)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.reflowTillNow(JavadocFormatter.java:561)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.visitStartElement(JavadocFormatter.java:256)
at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCStartElement.accept(DCTree.java:810)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:79)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.scan(JavadocFormatter.java:549)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scanAndReduce(DocTreeScanner.java:83)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:98)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.visitDocComment(JavadocFormatter.java:147)
at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCDocComment.accept(DCTree.java:132)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:79)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.scan(JavadocFormatter.java:549)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter.formatJavadoc(JavadocFormatter.java:118)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$ExpressionJavadocTask.lambda$perform$0(ConsoleIOContext.java:626)
at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1494)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:511)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$ExpressionJavadocTask.perform(ConsoleIOContext.java:632)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.complete(ConsoleIOContext.java:287)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.access$000(ConsoleIOContext.java:69)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$1.complete(ConsoleIOContext.java:100)
at jdk.internal.le/jdk.internal.jline.console.ConsoleReader.readLine(ConsoleReader.java:2684)
at jdk.internal.le/jdk.internal.jline.console.ConsoleReader.readLine(ConsoleReader.java:2279)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.readLine(ConsoleIOContext.java:139)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.run(JShellTool.java:1140)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.start(JShellTool.java:929)
at jdk.jshell/jdk.internal.jshell.tool.JShellToolBuilder.run(JShellToolBuilder.java:239)
at jdk.jshell/jdk.internal.jshell.tool.JShellToolProvider.main(JShellToolProvider.java:119)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
jshell should not crash
ACTUAL -
jshell crashes

ERROR MESSAGES/STACK TRACES THAT OCCUR :
jshell> HttpRequest.newBuilder().uri(new URI(Exception in thread "main" java.lang.StringIndexOutOfBoundsException: index 1230,length 1230
at java.base/java.lang.String.checkIndex(String.java:3075)
at java.base/java.lang.AbstractStringBuilder.charAt(AbstractStringBuilder.java:281)
at java.base/java.lang.StringBuilder.charAt(StringBuilder.java:77)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter.reflow(JavadocFormatter.java:590)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter.access$200(JavadocFormatter.java:70)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.reflowTillNow(JavadocFormatter.java:561)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.visitStartElement(JavadocFormatter.java:256)
at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCStartElement.accept(DCTree.java:810)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:79)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.scan(JavadocFormatter.java:549)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scanAndReduce(DocTreeScanner.java:83)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:98)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.visitDocComment(JavadocFormatter.java:147)
at jdk.compiler/com.sun.tools.javac.tree.DCTree$DCDocComment.accept(DCTree.java:132)
at jdk.compiler/com.sun.source.util.DocTreeScanner.scan(DocTreeScanner.java:79)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter$FormatJavadocScanner.scan(JavadocFormatter.java:549)
at jdk.compiler/jdk.internal.shellsupport.doc.JavadocFormatter.formatJavadoc(JavadocFormatter.java:118)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$ExpressionJavadocTask.lambda$perform$0(ConsoleIOContext.java:626)
at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1494)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:511)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$ExpressionJavadocTask.perform(ConsoleIOContext.java:632)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.complete(ConsoleIOContext.java:287)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.access$000(ConsoleIOContext.java:69)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$1.complete(ConsoleIOContext.java:100)
at jdk.internal.le/jdk.internal.jline.console.ConsoleReader.readLine(ConsoleReader.java:2684)
at jdk.internal.le/jdk.internal.jline.console.ConsoleReader.readLine(ConsoleReader.java:2279)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.readLine(ConsoleIOContext.java:139)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.run(JShellTool.java:1140)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.start(JShellTool.java:929)
at jdk.jshell/jdk.internal.jshell.tool.JShellToolBuilder.run(JShellToolBuilder.java:239)
at jdk.jshell/jdk.internal.jshell.tool.JShellToolProvider.main(JShellToolProvider.java:119)

REPRODUCIBILITY :
This bug can be reproduced always.