Refactor en route to #5027 -- remove usestring parameter from lookupvar

The usestring parameter to lookupvar was objectionable for several reasons;
first, it performed a function orthogonal to the main purpose of the method,
second its default was the least common value, and third it was causing other
code to work for reasons that were not obvious (extlookup).

This refactor breaks the value-transforming function out into a seperate
method which allows the user to specify the value to be used in lieu of :undef
and removes the parameter.  The function, Scope#undef_as(default,exp) is
written so that it can be used in user code (templates, functions, etc.) if
needed.

This refactor will introduce a user-visible behaviour change in the case where
users were counting on lookupvar to return "" for undefined variables.  The
best solution is to have them use undef_as, replacing:

    lookupvar('myvar')

with

    undef_as('',lookupvar('myvar'))

(with the option to specify another default value if desired).  If this is too
objectionable, we could rename the existing lookupvar as raw_lookupvar and
define

    def lookupvar(v)
      undef_as('',raw_lookupvar(v))
    end

to restore the present behaviour.

5 files changed, 25 insertions, 35 deletions

diff --git a/lib/puppet/parser/ast/leaf.rb b/lib/puppet/parser/ast/leaf.rb
index 77617e992..b61634d6c 100644
--- a/lib/puppet/parser/ast/leaf.rb
+++ b/lib/puppet/parser/ast/leaf.rb
@@ -124,7 +124,7 @@ class Puppet::Parser::AST
     # not include syntactical constructs, like '$' and '{}').
     def evaluate(scope)
       parsewrap do
-        if (var = scope.lookupvar(@value, false)) == :undefined
+        if (var = scope.lookupvar(@value)) == :undefined
           var = :undef
         end
         var
diff --git a/lib/puppet/parser/functions/extlookup.rb b/lib/puppet/parser/functions/extlookup.rb
index b5688d644..5fbf26cec 100644
--- a/lib/puppet/parser/functions/extlookup.rb
+++ b/lib/puppet/parser/functions/extlookup.rb
@@ -91,9 +91,9 @@ This is for back compatibility to interpolate variables with %. % interpolation
 
   raise Puppet::ParseError, ("extlookup(): wrong number of arguments (#{args.length}; must be <= 3)") if args.length > 3
 
-  extlookup_datadir = lookupvar('::extlookup_datadir')
+  extlookup_datadir = undef_as('',lookupvar('::extlookup_datadir'))
 
-  extlookup_precedence = lookupvar('::extlookup_precedence').collect { |var| var.gsub(/%\{(.+?)\}/) { lookupvar("::#{$1}") } }
+  extlookup_precedence = undef_as([],lookupvar('::extlookup_precedence')).collect { |var| var.gsub(/%\{(.+?)\}/) { lookupvar("::#{$1}") } }
 
   datafiles = Array.new
 
diff --git a/lib/puppet/parser/resource.rb b/lib/puppet/parser/resource.rb
index c007d4dbe..ace01bb4b 100644
--- a/lib/puppet/parser/resource.rb
+++ b/lib/puppet/parser/resource.rb
@@ -241,7 +241,7 @@ class Puppet::Parser::Resource < Puppet::Resource
 
   def add_backward_compatible_relationship_param(name)
     # Skip metaparams for which we get no value.
-    return unless val = scope.lookupvar(name.to_s, false) and val != :undefined
+    return unless val = scope.lookupvar(name.to_s) and val != :undefined
 
     # The default case: just set the value
     set_parameter(name, val) and return unless @parameters[name]
diff --git a/lib/puppet/parser/scope.rb b/lib/puppet/parser/scope.rb
index 07347552b..df307915e 100644
--- a/lib/puppet/parser/scope.rb
+++ b/lib/puppet/parser/scope.rb
@@ -210,45 +210,41 @@ class Puppet::Parser::Scope
     find_definition(name) || find_hostclass(name)
   end
 
-  def lookup_qualified_var(name, usestring)
+  def undef_as(x,v)
+    (v == :undefined) ? x : (v == :undef) ? x : v
+  end
+
+  def lookup_qualified_var(name)
     parts = name.split(/::/)
     shortname = parts.pop
     klassname = parts.join("::")
     klass = find_hostclass(klassname)
     unless klass
       warning "Could not look up qualified variable '#{name}'; class #{klassname} could not be found"
-      return usestring ? "" : :undefined
+      return :undefined
     end
     unless kscope = class_scope(klass)
       warning "Could not look up qualified variable '#{name}'; class #{klassname} has not been evaluated"
-      return usestring ? "" : :undefined
+      return :undefined
     end
-    kscope.lookupvar(shortname, usestring)
+    kscope.lookupvar(shortname)
   end
 
   private :lookup_qualified_var
 
-  # Look up a variable.  The simplest value search we do.  Default to returning
-  # an empty string for missing values, but support returning a constant.
-  def lookupvar(name, usestring = true)
+  # Look up a variable.  The simplest value search we do.  
+  def lookupvar(name)
     table = ephemeral?(name) ? @ephemeral.last : @symtable
     # If the variable is qualified, then find the specified scope and look the variable up there instead.
     if name =~ /::/
-      return lookup_qualified_var(name, usestring)
-    end
-    # We can't use "if table[name]" here because the value might be false
-    if ephemeral_include?(name) or table.include?(name)
-      if usestring and table[name] == :undef
-        return ""
-      else
-        return table[name]
-      end
-    elsif self.parent
-      return parent.lookupvar(name, usestring)
-    elsif usestring
-      return ""
+      lookup_qualified_var(name)
+    elsif ephemeral_include?(name) or table.include?(name)
+      # We can't use "if table[name]" here because the value might be false
+      table[name]
+    elsif parent
+      parent.lookupvar(name)
     else
-      return :undefined
+      :undefined
     end
   end
 
@@ -333,7 +329,7 @@ class Puppet::Parser::Scope
       table[name] = value
     else # append case
       # lookup the value in the scope if it exists and insert the var
-      table[name] = lookupvar(name)
+      table[name] = undef_as('',lookupvar(name))
       # concatenate if string, append if array, nothing for other types
       case value
       when Array
@@ -363,7 +359,7 @@ class Puppet::Parser::Scope
           if var and var =~ /^[0-9]+$/ and not ephemeral_include?(var)
             next
           end
-          out << lookupvar(var).to_s || ""
+          out << undef_as('',lookupvar(var)).to_s
         end
       elsif ss.scan(/^\\(.)/)
         # Puppet.debug("Got escape: pos:%d; m:%s" % [ss.pos, ss.matched])
diff --git a/lib/puppet/parser/templatewrapper.rb b/lib/puppet/parser/templatewrapper.rb
index 6864aa1a9..73fcb8aac 100644
--- a/lib/puppet/parser/templatewrapper.rb
+++ b/lib/puppet/parser/templatewrapper.rb
@@ -20,11 +20,7 @@ class Puppet::Parser::TemplateWrapper
 
   # Should return true if a variable is defined, false if it is not
   def has_variable?(name)
-    if scope.lookupvar(name.to_s, false) != :undefined
-      true
-    else
-      false
-    end
+    scope.lookupvar(name.to_s) != :undefined
   end
 
   # Allow templates to access the defined classes
@@ -55,9 +51,7 @@ class Puppet::Parser::TemplateWrapper
   # the missing_method definition here until we declare the syntax finally
   # dead.
   def method_missing(name, *args)
-    # We have to tell lookupvar to return :undefined to us when
-    # appropriate; otherwise it converts to "".
-    value = scope.lookupvar(name.to_s, false)
+    value = scope.lookupvar(name.to_s)
     if value != :undefined
       return value
     else