On 23.05.2017 22:30, Alex Buckley wrote:
On 5/23/2017 12:54 PM, Stephan Herrmann wrote:
The 2017-05-18 draft of JLS indicates that automatic modules are beyond the
scope of JLS.
I'm puzzled what that should mean for a compiler.
At face value it seems to say that compilers need not care about automatic
modules. Instead I'd expect JLS to state that the host system must be able
to discover automatic modules "as if by invocation of
ModuleFinder.of(Path...)." or similar.
Which is it?
Can you quote the text of concern?
JLS 7.7:
"The Java programming language does not distinguish between (i) named modules
specified
explicitly in module declarations and (ii) named modules specified
implicitly by the Java
Platform Module System, that is, automatic modules. A module declaration
refers to other
named modules without being aware of the manner in which they were
specified."
Automatic modules are not a source artifact, so their specification is found in the API portion of the JPMS spec rather than in the
JLS. The JLS has traditionally not specified how a compiler interprets non-source artifacts, e.g., the JLS says nothing about
whether the host system understands a "class path" or that such a thing might identify non-source artifacts like JAR files. The
analog in the Java SE 9 era is that it's up to a compiler to choose to support a thing called the "module path" and to identify
non-source artifacts on it; I do not see how the JLS can say anything for that. Once a compiler has made the choice, then the JPMS
specifies that certain non-source artifacts must be interpreted as automatic modules, at which point they're "just" named modules
that a modular compilation unit's 'requires' directive can refer to.
There's a decisive difference: for .class files (in the file system or in a
.jar)
the compiler "knows" what it means, because .class files are well in the realm
of
compilers. There are no hidden semantics.
A jar-as-automatic-module has semantics that are not known to the compiler,
unless JLS specifies s.t. to this end.
I wasn't concerned about the module-path aspect of it, just about the semantics
of
those modules for which no descriptor exists.
Stephan
