Add a cyglink Tool to handle linking of shared libraries under

From: David Rothenberger <daveroth@acm.org>

Cygwin. The tool handles creating the DLL import library as well as
replacing the initial "lib" with "cyg".
---
 MANIFEST                      |    1 
 engine/SCons/Tool/__init__.py |    8 +++
 engine/SCons/Tool/cyglink.py  |   96 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 105 insertions(+), 0 deletions(-)
 create mode 100644 engine/SCons/Tool/cyglink.py

diff --git a/MANIFEST b/MANIFEST
index e652610..8ed840c 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -83,6 +83,7 @@ engine/SCons/Tool/as.py
 engine/SCons/Tool/bcc32.py
 engine/SCons/Tool/c++.py
 engine/SCons/Tool/cc.py
+engine/SCons/Tool/cyglink.py
 engine/SCons/Tool/cvf.py
 engine/SCons/Tool/default.py
 engine/SCons/Tool/dmd.py
diff --git a/engine/SCons/Tool/__init__.py b/engine/SCons/Tool/__init__.py
index b12095f..a15526e 100644
--- a/engine/SCons/Tool/__init__.py
+++ b/engine/SCons/Tool/__init__.py
@@ -733,6 +733,14 @@ def tool_list(platform, env):
         assemblers = ['as']
         fortran_compilers = ['gfortran', 'f95', 'f90', 'g77']
         ars = ['ar']
+    elif str(platform) == 'cygwin':
+        "prefer GNU tools on Cygwin, except for a platform-specific linker"
+        linkers = ['cyglink', 'mslink', 'ilink']
+        c_compilers = ['gcc', 'msvc', 'intelc', 'icc', 'cc']
+        cxx_compilers = ['g++', 'msvc', 'intelc', 'icc', 'c++']
+        assemblers = ['gas', 'nasm', 'masm']
+        fortran_compilers = ['gfortran', 'g77', 'ifort', 'ifl', 'f95', 'f90', 'f77']
+        ars = ['ar', 'mslib']
     else:
         "prefer GNU tools on all other platforms"
         linkers = ['gnulink', 'mslink', 'ilink']
diff --git a/engine/SCons/Tool/cyglink.py b/engine/SCons/Tool/cyglink.py
new file mode 100644
index 0000000..768c1ac
--- /dev/null
+++ b/engine/SCons/Tool/cyglink.py
@@ -0,0 +1,96 @@
+"""SCons.Tool.cyglink
+
+Customization of gnulink for Cygwin (http://www.cygwin.com/)
+
+There normally shouldn't be any need to import this module directly.
+It will usually be imported through the generic SCons.Tool.Tool()
+selection method.
+
+"""
+
+import SCons.Action
+import SCons.Util
+
+import gnulink
+
+def shlib_generator(target, source, env, for_signature):
+    cmd = SCons.Util.CLVar(['$SHLINK']) 
+
+    dll = env.FindIxes(target, 'CYGDLLPREFIX', 'CYGDLLSUFFIX')
+    if dll: cmd.extend(['-o', dll])
+
+    cmd.extend(['$SHLINKFLAGS', '$__RPATH'])
+
+    implib = env.FindIxes(target, 'IMPLIBPREFIX', 'IMPLIBSUFFIX')
+    if implib:
+        cmd.extend([
+            '-Wl,--out-implib='+implib.get_string(for_signature),
+            '-Wl,--export-all-symbols',
+            '-Wl,--enable-auto-import',
+            '-Wl,--whole-archive', '$SOURCES',
+            '-Wl,--no-whole-archive', '$_LIBDIRFLAGS', '$_LIBFLAGS'
+            ])
+    
+    return [cmd]
+
+def shlib_emitter(target, source, env):
+    dll = env.FindIxes(target, 'SHLIBPREFIX', 'SHLIBSUFFIX')
+    no_import_lib = env.get('no_import_lib', 0)
+
+    if not dll:
+        raise SCons.Errors.UserError("A shared library should have exactly one target with the suffix: %s" % env.subst("$SHLIBSUFFIX"))
+    
+    # Remove any "lib" after the prefix
+    pre = env.subst('$SHLIBPREFIX')
+    dllName = str(dll)
+    if dllName[len(pre):len(pre)+3] == 'lib':
+        dllName = dllName[len(pre)+3:]
+        dll = env.fs.File(dllName)
+
+    dll = env.ReplaceIxes(dll,
+                          'SHLIBPREFIX', 'SHLIBSUFFIX',
+                          'CYGDLLPREFIX', 'CYGDLLSUFFIX')
+
+    origTarget = target
+    target = [env.fs.File(dll)]
+
+    # Append an import lib target
+    if not no_import_lib and \
+       not env.FindIxes(origTarget, 'IMPLIBPREFIX', 'IMPLIBSUFFIX'):
+
+        # Create list of target libraries as strings
+        targetStrings = env.ReplaceIxes(origTarget[0],
+                                        'SHLIBPREFIX', 'SHLIBSUFFIX',
+                                        'IMPLIBPREFIX', 'IMPLIBSUFFIX')
+        
+        # Now add file nodes to target list
+        target.append(env.fs.File(targetStrings))
+
+    return (target, source)
+                         
+
+shlib_action = SCons.Action.Action(shlib_generator, generator=1)
+
+def generate(env):
+    """Add Builders and construction variables for cyglink to an Environment."""
+    gnulink.generate(env)
+
+    env['SHLINKCOM'] = shlib_action
+    env['LDMODULECOM'] = shlib_action
+    env.Append(SHLIBEMITTER = [shlib_emitter])
+
+    env['CYGDLLPREFIX']        = 'cyg'
+    env['CYGDLLSUFFIX']        = '.dll'
+
+    env['IMPLIBPREFIX']        = ''
+    env['IMPLIBSUFFIX']        = '.dll.a'
+
+def exists(env):
+    return gnulink.exists(env)
+
+
+# Local Variables:
+# tab-width:4
+# indent-tabs-mode:nil
+# End:
+# vim: set expandtab tabstop=4 shiftwidth=4: