Add customization point for easyblocks to specify additional paramete…

…rs for "sources"

Some easyblocks such as `Cargo` will use a custom EasyConfig parameters
to fill the `sources` list.
To avoid hard-coding them `inject_checksums` introduce a static method
`src_parameter_names` to return a list of parameters that contribute to
the final list of `sources` when parsing the EasyConfig.

easybuild/framework/easyblock.py

@@ -138,6 +138,14 @@ def extra_options(extra=None):
 
         return extra
 
+    @staticmethod
+    def src_keys():
+        """
+        Return list of EasyConfig parameter that contribute to the sources in the `src` member
+        (or equivalently to the `sources` parameter of a parsed EasyConfig)
+        """
+        return ['sources']
+
     #
     # INIT
     #
@@ -4752,7 +4760,7 @@ def make_checksum_lines(checksums, indent_level):
             placeholder = '# PLACEHOLDER FOR SOURCES/PATCHES WITH CHECKSUMS'
 
             # grab raw lines for the following params
-            keys = ['source_urls', 'sources', 'crates', 'patches']
+            keys = ['source_urls'] + app.src_keys() + ['patches']
             raw = {}
             for key in keys:
                 regex = re.compile(r'^(%s(?:.|\n)*?\])\s*$' % key, re.M)

test/framework/sandbox/easybuild/easyblocks/generic/cargo.py

@@ -37,6 +37,10 @@ def extra_options():
         }
         return EasyBlock.extra_options(extra_vars)
 
+    @staticmethod
+    def src_keys():
+        return super(Cargo, Cargo).src_keys() + ['crates']
+
     def __init__(self, *args, **kwargs):
         """Constructor for Cargo easyblock."""
         super(Cargo, self).__init__(*args, **kwargs)