use source toolchain version when passing only --try-toolchain

`process_software_build_specs` ialways adds a `toolchain` key
even when only the name of the toolchain is available.
This makes the code in `tweak` ignore the code path in using
`toolchain_name` and/or `toolchain_version` with the fallback to using
the values of the source toolchain.
This in turn leads to failures further down when a value of `None` is
used where an actual version is expected.

Fix by only adding the `toolchain` key when we have both the name and
version and hence a complete, valid toolchain spec.

easybuild/tools/options.py

@@ -1735,11 +1735,13 @@ def process_software_build_specs(options):
             })
 
     # provide both toolchain and toolchain_name/toolchain_version keys
-    if 'toolchain_name' in build_specs:
+    try:
         build_specs['toolchain'] = {
             'name': build_specs['toolchain_name'],
-            'version': build_specs.get('toolchain_version', None),
+            'version': build_specs['toolchain_version'],
         }
+    except KeyError:
+        pass  # Don't set toolchain key if we don't have both keys
 
     # process --amend and --try-amend
     if options.amend or options.try_amend:

test/framework/easyconfigs/test_ecs/i/iimpi/iimpi-2018a.eb

@@ -0,0 +1,20 @@
+# This is an easyconfig file for EasyBuild, see http://easybuilders.github.io/easybuild
+easyblock = 'Toolchain'
+
+name = 'iimpi'
+version = '2018a'
+
+homepage = 'https://software.intel.com/parallel-studio-xe'
+description = """Intel C/C++ and Fortran compilers, alongside Intel MPI."""
+
+toolchain = SYSTEM
+
+local_compver = '2016.1.150'
+local_suff = '-GCC-4.9.3-2.25'
+dependencies = [
+    ('icc', local_compver, local_suff),
+    ('ifort', local_compver, local_suff),
+    ('impi', '5.1.2.150', '', ('iccifort', '%s%s' % (local_compver, local_suff))),
+]
+
+moduleclass = 'toolchain'

test/framework/easyconfigs/test_ecs/i/intel/intel-2018a.eb

@@ -8,14 +8,17 @@ description = """Intel Cluster Toolkit Compiler Edition provides Intel C/C++ and
 
 toolchain = SYSTEM
 
+local_compver = '2016.1.150'
+local_gccver = '4.9.3'
+local_binutilsver = '2.25'
+local_gccsuff = '-GCC-%s-%s' % (local_gccver, local_binutilsver)
 # fake intel toolchain easyconfig, no dependencies (good enough for testing)
 local_fake_dependencies = [
-    ('GCCcore', '6.4.0'),
-    ('binutils', '2.28', '-GCCcore-6.4.0'),
-    ('icc', '2018.1.163', '-GCCcore-6.4.0'),
-    ('ifort', '2018.1.163', '-GCCcore-6.4.0'),
-    ('impi', '2018.1.163', '', ('iccifort', '2018.1.163-GCCcore-6.4.0')),
-    ('imkl', '2018.1.163', '', ('iimpi', version)),
+    ('GCCcore', local_gccver),
+    ('binutils', local_binutilsver, '-GCCcore-%s' % local_gccver),
+    ('icc', local_compver, local_gccsuff),
+    ('ifort', local_compver, local_gccsuff),
+    ('impi', '5.1.2.150', '', ('iccifort', '%s%s' % (local_compver, local_gccsuff))),
 ]
 
 moduleclass = 'toolchain'

test/framework/easyconfigs/test_ecs/t/toy/toy-0.0-foss-2018a.eb

@@ -0,0 +1,33 @@
+name = 'toy'
+version = '0.0'
+
+homepage = 'https://easybuilders.github.io/easybuild'
+description = "Toy C program, 100% toy."
+
+toolchain = {'name': 'foss', 'version': '2018a'}
+toolchainopts = {'pic': True, 'opt': True, 'optarch': True}
+
+sources = [SOURCE_TAR_GZ]
+checksums = [[
+    'be662daa971a640e40be5c804d9d7d10',  # default (MD5)
+    '44332000aa33b99ad1e00cbd1a7da769220d74647060a10e807b916d73ea27bc',  # default (SHA256)
+    ('adler32', '0x998410035'),
+    ('crc32', '0x1553842328'),
+    ('md5', 'be662daa971a640e40be5c804d9d7d10'),
+    ('sha1', 'f618096c52244539d0e89867405f573fdb0b55b0'),
+    ('size', 273),
+]]
+patches = [
+    'toy-0.0_fix-silly-typo-in-printf-statement.patch',
+    ('toy-extra.txt', 'toy-0.0'),
+]
+
+sanity_check_paths = {
+    'files': [('bin/yot', 'bin/toy')],
+    'dirs': ['bin'],
+}
+
+postinstallcmds = ["echo TOY > %(installdir)s/README"]
+
+moduleclass = 'tools'
+# trailing comment, leave this here, it may trigger bugs with extract_comments()

test/framework/options.py

@@ -2420,6 +2420,19 @@ def test_try(self):
         allargs = args + ['--software-version=1.2.3', '--toolchain=gompi,2018a']
         self.assertErrorRegex(EasyBuildError, "version .* not available", self.eb_main, allargs, raise_error=True)
 
+        # Try changing only name or version of toolchain
+        args.pop(0)  # Remove EC filename
+        test_cases = [
+            (['toy-0.0-gompi-2018a.eb', '--try-toolchain-name=intel'], 'toy/0.0-iimpi-2018a'),
+            (['toy-0.0-foss-2018a.eb', '--try-toolchain-name=intel'], 'toy/0.0-intel-2018a'),
+            (['toy-0.0-gompi-2018a.eb', '--try-toolchain-version=2018b'], 'toy/0.0-gompi-2018b'),
+        ]
+        for extra_args, mod in test_cases:
+            outtxt = self.eb_main(args + extra_args, verbose=True, raise_error=True)
+            mod_regex = re.compile(r"\(module: %s\)$" % mod, re.M)
+            self.assertTrue(mod_regex.search(outtxt), "Pattern %s found in %s" % (mod_regex.pattern, outtxt))
+
+
     def test_try_with_copy(self):
         """Test whether --try options are taken into account."""
         ecs_path = os.path.join(os.path.dirname(os.path.abspath(__file__)), 'easyconfigs', 'test_ecs')