guix: ant-build-system: Add main-class support.

* guix/build-system/ant.scm: New #:main-class argument
* guix/build/ant-build-system.scm: Generate a manifest file with
additional properties.
* doc/guix.texi (Build Systems): Document it.

doc/guix.texi

@@ -3479,6 +3479,10 @@ build file @file{build.xml} with tasks to build the specified jar
 archive.  In this case the parameter @code{#:source-dir} can be used to
 specify the source sub-directory, defaulting to ``src''.
+The @code{#:main-class} parameter can be used with the minimal ant 
+buildfile to specify the main class of the resulting jar.  This makes the 
+jar file executable.
+
 The parameter @code{#:build-target} can be used to specify the Ant task
 that should be run during the @code{build} phase.  By default the
 ``jar'' task will be run.

guix/build-system/ant.scm

@@ -99,6 +99,7 @@ (define* (ant-build store name inputs
                     (make-flags ''())
                     (build-target "jar")
                     (jar-name #f)
+                    (main-class #f)
                     (source-dir "src")
                     (test-dir "src/test")
                     (phases '(@ (guix build ant-build-system)
@@ -130,6 +131,7 @@ (define builder
                   #:test-target ,test-target
                   #:build-target ,build-target
                   #:jar-name ,jar-name
+                  #:main-class ,main-class
                   #:source-dir ,source-dir
                   #:test-dir ,test-dir
                   #:phases ,phases

guix/build/ant-build-system.scm

@@ -36,7 +36,7 @@ (define-module (guix build ant-build-system)
 ;; Code:
 
 (define* (default-build.xml jar-name prefix #:optional
-                            (source-dir ".") (test-dir "./test"))
+                            (source-dir ".") (test-dir "./test") (main-class #f))
   "Create a simple build.xml with standard targets for Ant."
   (call-with-output-file "build.xml"
     (lambda (port)
@@ -44,6 +44,10 @@ (define* (default-build.xml jar-name prefix #:optional
        `(project (@ (basedir "."))
                  (property (@ (name "classes.dir")
                               (value "${basedir}/build/classes")))
+                 (property (@ (name "manifest.dir")
+                              (value "${basedir}/build/manifest")))
+                 (property (@ (name "manifest.file")
+                              (value "${manifest.dir}/MANIFEST.MF")))
                  (property (@ (name "jar.dir")
                               (value "${basedir}/build/jar")))
                  (property (@ (name "dist.dir")
@@ -60,6 +64,17 @@ (define* (default-build.xml jar-name prefix #:optional
                  (path (@ (id "classpath"))
                        (pathelement (@ (location "${env.CLASSPATH}"))))
 
+                 (target (@ (name "manifest"))
+                         (mkdir (@ (dir "${manifest.dir}")))
+                         (echo (@ (file "${manifest.file}")
+                                  (message ,(string-append
+                                              (if main-class
+                                                (string-append
+                                                  "Main-Class: " main-class
+                                                  "${line.separator}")
+                                                "")
+                                              "")))))
+
                  (target (@ (name "compile"))
                          (mkdir (@ (dir "${classes.dir}")))
                          (javac (@ (includeantruntime "false")
@@ -97,10 +112,11 @@ (define* (default-build.xml jar-name prefix #:optional
                                                     (include (@ (name "**/*Test.java" )))))))
 
                  (target (@ (name "jar")
-                            (depends "compile"))
+                            (depends "compile, manifest"))
                          (mkdir (@ (dir "${jar.dir}")))
                          (exec (@ (executable "jar"))
-                               (arg (@ (line ,(string-append "-cf ${jar.dir}/" jar-name
+                               (arg (@ (line ,(string-append "-cmf ${manifest.file} "
+                                                             "${jar.dir}/" jar-name
                                                              " -C ${classes.dir} ."))))))
 
                  (target (@ (name "install"))
@@ -133,12 +149,13 @@ (define* (unpack #:key source #:allow-other-keys)
 
 (define* (configure #:key inputs outputs (jar-name #f)
                     (source-dir "src")
-                    (test-dir "src/test") #:allow-other-keys)
+                    (test-dir "src/test")
+                    (main-class #f) #:allow-other-keys)
   (when jar-name
     (default-build.xml jar-name
                        (string-append (assoc-ref outputs "out")
                                       "/share/java")
-                       source-dir test-dir))
+                       source-dir test-dir main-class))
   (setenv "JAVA_HOME" (assoc-ref inputs "jdk"))
   (setenv "CLASSPATH" (generate-classpath inputs)))