build: Improve value substitution

The waf build system uses lists for tool flags.  The build items may use
variable substitution.  Add the ability to use the variable substitution in
lists.  For example:

MORE_FLAGS = ['-more', '-flags']

flags:
- -some-flag
- ${MORE_FLAGS}

Before this change, the ${MORE_FLAGS} was substituted to "-more -flags".  This
would be passed by waf as a single command line argument to the tool.

After this change, the ${MORE_FLAGS} list extends the flags list:

flags = ['-some-flag', '-more', '-flags']

This list extension is performed if a list element consists of exactly one
variable.

Update #4670.

1 files changed, 16 insertions, 9 deletions

diff --git a/wscript b/wscript
index 731d1402ff..6ad230aca5 100755
--- a/wscript
+++ b/wscript
@@ -115,6 +115,9 @@ class Template(string.Template):
     idpattern = "[_A-Za-z][_A-Za-z0-9:#]*"
 
 
+_VAR_PATTERN = re.compile("\$\{?(" + Template.idpattern + ")\}?$")
+
+
 def _is_enabled_op_and(enabled, enabled_by):
     for next_enabled_by in enabled_by:
         if not _is_enabled(enabled, next_enabled_by):
@@ -249,18 +252,22 @@ class Item(object):
                     )
                 )
         if isinstance(value, list):
-            return [self.substitute(ctx, subvalue) for subvalue in value]
+            more = []
+            for item in value:
+                if isinstance(item, str):
+                    m = _VAR_PATTERN.match(item)
+                else:
+                    m = None
+                if m:
+                    more.extend(ctx.env[m.group(1).strip("{}")])
+                else:
+                    more.append(self.substitute(ctx, item))
+            return more
         return value
 
     def get(self, ctx, name):
         return self.substitute(ctx, self.data[name])
 
-    def get_values(self, ctx, name):
-        more = []
-        for value in self.data[name]:
-            more.extend(self.substitute(ctx, value).split())
-        return more
-
     def install_target(self, bld):
         install_path = self.data["install-path"]
         if install_path:
@@ -512,12 +519,12 @@ class GroupItem(Item):
 
     def prepare_build(self, bld, bic):
         return BuildItemContext(
-            bic.includes + self.get_values(bld, "includes"),
+            bic.includes + self.substitute(bld, self.data["includes"]),
             bic.cppflags,
             bic.cflags,
             bic.cxxflags,
             self.data["use-before"] + bic.use + self.data["use-after"],
-            bic.ldflags + self.get_values(bld, "ldflags"),
+            bic.ldflags + self.substitute(bld, self.data["ldflags"]),
             bic.objects,
         )