A simple inline comment crashes compiler with NPE

[hubertp]

main args =
    v = 42 ## meh
    v

will blow up:

> ./built-distribution/enso-engine-0.0.0-dev-linux-amd64/enso-0.0.0-dev/bin/enso --run simple-crash.enso

[ERROR] [enso.org.enso.compiler.Compiler] Encountered a critical failure while parsing module
java.lang.NullPointerException: Cannot invoke "org.enso.compiler.core.ir.Expression.transformExpressions(scala.PartialFunction)" because "x$1" is null
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.$anonfun$transformExpressions$1(Expression.scala:24)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.CallArgument$Specified.mapExpressions(CallArgument.scala:124)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.CallArgument$Specified.mapExpressions(CallArgument.scala:43)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.expression.Application$Prefix.$anonfun$mapExpressions$1(Application.scala:144)
	at [email protected]/scala.collection.immutable.List.map(List.scala:246)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.expression.Application$Prefix.mapExpressions(Application.scala:144)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.expression.Application$Prefix.mapExpressions(Application.scala:24)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.transformExpressions(Expression.scala:24)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.transformExpressions$(Expression.scala:18)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.expression.Application$Prefix.transformExpressions(Application.scala:24)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.$anonfun$transformExpressions$1(Expression.scala:24)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression$Binding.mapExpressions(Expression.scala:280)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression$Binding.mapExpressions(Expression.scala:192)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.transformExpressions(Expression.scala:24)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.transformExpressions$(Expression.scala:18)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression$Binding.transformExpressions(Expression.scala:192)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$.org$enso$compiler$pass$resolve$DocumentationComments$$resolveExpression(DocumentationComments.scala:83)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$$anonfun$org$enso$compiler$pass$resolve$DocumentationComments$$resolveExpression$1.$anonfun$applyOrElse$1(DocumentationComments.scala:86)
	at [email protected]/scala.collection.immutable.List.map(List.scala:246)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$$anonfun$org$enso$compiler$pass$resolve$DocumentationComments$$resolveExpression$1.applyOrElse(DocumentationComments.scala:86)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$$anonfun$org$enso$compiler$pass$resolve$DocumentationComments$$resolveExpression$1.applyOrElse(DocumentationComments.scala:83)
	at [email protected]/scala.runtime.AbstractPartialFunction.apply(AbstractPartialFunction.scala:35)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.transformExpressions(Expression.scala:22)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression.transformExpressions$(Expression.scala:18)
	at org.enso.runtime.parser/org.enso.compiler.core.ir.Expression$Block.transformExpressions(Expression.scala:57)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$.org$enso$compiler$pass$resolve$DocumentationComments$$resolveExpression(DocumentationComments.scala:83)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$.resolveDefinition(DocumentationComments.scala:167)
	at org.enso.runtime.compiler/org.enso.compiler.pass.resolve.DocumentationComments$.$anonfun$resolveModule$5(DocumentationComments.scala:211)
	at [email protected]/scala.collection.immutable.List.map(List.scala:246)
...

[kazcw]

The AST looks reasonable:

> echo -en 'foo ## bar\nbaz' | cargo run -p enso-parser-debug --bin enso-parser-debug
(BodyBlock #(
 (App (Ident foo) (Documented (#((Section " bar")) #()) ()))
 (Ident baz)))

A syntax warning would be nice, since documentation at the end of a line is not supported (the documentation could be associated with the preceding content, but this is not a planned feature AFAIK); I added this to a (new) syntax-warning wishlist issue.