Fix #3155 - prevent error when using two matching regex in cascade

The following manifest:
case $var {
  /match/: {
     if $var =~ /matchagain/ {
     }
  }
}

is failing because the "=~" operators when matching sets an ephemeral
variable in the scope. But the case regex also did it, and since they
both belong to the same scope, and Puppet variables are immutables, the
scope raises an error.

This patch fixes this issue by adding to the current scope a stack
of ephemeral symbol tables. Each new match operator or case/selector
with regex adds a new scope. When we get out of the case/if/selector
structure the scope is reset to the ephemeral level we were when
entering it.

This way the following manifest produces the correct output:
case $var {
  /match(rematch)/: {
     notice("1. \$0 = $0, \$1 = $1")
     if $var =~ /matchagain/ {
         notice("2. \$0 = $0, \$1 = $1")
     }
     notice("3. \$0 = $0, \$1 = $1")
  }
}
notice("4. \$0 = $0")

And the output is:
1. $0 = match, $1 = rematch
2. $0 = matchagain, $1 = rematch
3. $0 = match, $1 = rematch
4. $0 =

Signed-off-by: Brice Figureau <brice-puppet@daysofwonder.com>

4 files changed, 68 insertions, 12 deletions

diff --git a/lib/puppet/parser/ast/casestatement.rb b/lib/puppet/parser/ast/casestatement.rb
index 64298cac3..ed1bb8aa3 100644
--- a/lib/puppet/parser/ast/casestatement.rb
+++ b/lib/puppet/parser/ast/casestatement.rb
@@ -11,6 +11,8 @@ class Puppet::Parser::AST
         # Short-curcuit evaluation.  Return the value of the statements for
         # the first option that matches.
         def evaluate(scope)
+            level = scope.ephemeral_level
+
             value = @test.safeevaluate(scope)
 
             retvalue = nil
@@ -32,7 +34,7 @@ class Puppet::Parser::AST
             Puppet.debug "No true answers and no default"
             return nil
         ensure
-            scope.unset_ephemeral_var
+            scope.unset_ephemeral_var(level)
         end
 
         def each
diff --git a/lib/puppet/parser/ast/ifstatement.rb b/lib/puppet/parser/ast/ifstatement.rb
index 9d52123b6..d84445bbd 100644
--- a/lib/puppet/parser/ast/ifstatement.rb
+++ b/lib/puppet/parser/ast/ifstatement.rb
@@ -16,6 +16,7 @@ class Puppet::Parser::AST
         # else if there's an 'else' setting, evaluate it.
         # the first option that matches.
         def evaluate(scope)
+            level = scope.ephemeral_level
             value = @test.safeevaluate(scope)
 
             # let's emulate a new scope for each branches
@@ -30,7 +31,7 @@ class Puppet::Parser::AST
                     end
                 end
             ensure
-                scope.unset_ephemeral_var
+                scope.unset_ephemeral_var(level)
             end
         end
     end
diff --git a/lib/puppet/parser/ast/selector.rb b/lib/puppet/parser/ast/selector.rb
index ce834b63b..cc468a536 100644
--- a/lib/puppet/parser/ast/selector.rb
+++ b/lib/puppet/parser/ast/selector.rb
@@ -12,6 +12,7 @@ class Puppet::Parser::AST
 
         # Find the value that corresponds with the test.
         def evaluate(scope)
+            level = scope.ephemeral_level
             # Get our parameter.
             paramvalue = @param.safeevaluate(scope)
 
@@ -37,7 +38,7 @@ class Puppet::Parser::AST
 
             self.fail Puppet::ParseError, "No matching value for selector param '%s'" % paramvalue
         ensure
-            scope.unset_ephemeral_var
+            scope.unset_ephemeral_var(level)
         end
 
         def to_s
diff --git a/lib/puppet/parser/scope.rb b/lib/puppet/parser/scope.rb
index d6d663041..3623f40e2 100644
--- a/lib/puppet/parser/scope.rb
+++ b/lib/puppet/parser/scope.rb
@@ -20,6 +20,30 @@ class Puppet::Parser::Scope
     attr_accessor :top, :translated, :compiler
     attr_writer :parent
 
+    # thin wrapper around an ephemeral
+    # symbol table.
+    # when a symbol
+    class Ephemeral
+        def initialize(parent=nil)
+            @symbols = {}
+            @parent = parent
+        end
+
+        [:include?, :delete, :[]=].each do |m|
+            define_method(m) do |*args|
+                @symbols.send(m, *args)
+            end
+        end
+
+        def [](name)
+            unless @symbols.include?(name) or @parent.nil?
+                @parent[name]
+            else
+                @symbols[name]
+            end
+        end
+    end
+
     # A demeterific shortcut to the catalog.
     def catalog
         compiler.catalog
@@ -131,7 +155,9 @@ class Puppet::Parser::Scope
         # the ephemeral symbol tables
         # those should not persist long, and are used for the moment only
         # for $0..$xy capture variables of regexes
-        @ephemeral = {}
+        # this is actually implemented as a stack, with each ephemeral scope
+        # shadowing the previous one
+        @ephemeral = [ Ephemeral.new ]
 
         # All of the defaults set for types.  It's a hash of hashes,
         # with the first key being the type, then the second key being
@@ -194,13 +220,13 @@ class Puppet::Parser::Scope
     # 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)
-        table = ephemeral?(name) ? @ephemeral : @symtable
+        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 table.include?(name)
+        if ephemeral_include?(name) or table.include?(name)
             if usestring and table[name] == :undef
                 return ""
             else
@@ -293,7 +319,7 @@ class Puppet::Parser::Scope
     # in scopes above, but will not allow variables in the current scope
     # to be reassigned.
     def setvar(name,value, options = {})
-        table = options[:ephemeral] ? @ephemeral : @symtable
+        table = options[:ephemeral] ? @ephemeral.last : @symtable
         #Puppet.debug "Setting %s to '%s' at level %s mode append %s" %
         #    [name.inspect,value,self.level, append]
         if table.include?(name)
@@ -338,7 +364,7 @@ class Puppet::Parser::Scope
                 else # look the variable up
                     # make sure $0-$9 are lookupable only if ephemeral
                     var = ss[1] || ss[3] || ss[4]
-                    if var and var =~ /^[0-9]+$/ and not ephemeral?(var)
+                    if var and var =~ /^[0-9]+$/ and not ephemeral_include?(var)
                         next
                     end
                     out << lookupvar(var).to_s || ""
@@ -403,23 +429,49 @@ class Puppet::Parser::Scope
 
     # Undefine a variable; only used for testing.
     def unsetvar(var)
-        table = ephemeral?(var) ? @ephemeral : @symtable
+        table = ephemeral?(var) ? @ephemeral.last : @symtable
         if table.include?(var)
             table.delete(var)
         end
     end
 
-    def unset_ephemeral_var
-        @ephemeral = {}
+    # remove ephemeral scope up to level
+    def unset_ephemeral_var(level=:all)
+        if level == :all
+            @ephemeral = [ Ephemeral.new ]
+        else
+            (@ephemeral.size - level).times do 
+                @ephemeral.pop
+            end
+        end
+    end
+
+    # check if name exists in one of the ephemeral scope.
+    def ephemeral_include?(name)
+        @ephemeral.reverse.each do |eph|
+            return true if eph.include?(name)
+        end
+        false
     end
 
+    # is name an ephemeral variable?
     def ephemeral?(name)
-        @ephemeral.include?(name)
+        name =~ /^\d+$/
+    end
+
+    def ephemeral_level
+        @ephemeral.size
+    end
+
+    def new_ephemeral
+        @ephemeral.push(Ephemeral.new(@ephemeral.last))
     end
 
     def ephemeral_from(match, file = nil, line = nil)
         raise(ArgumentError,"Invalid regex match data") unless match.is_a?(MatchData)
 
+        new_ephemeral
+
         setvar("0", match[0], :file => file, :line => line, :ephemeral => true)
         match.captures.each_with_index do |m,i|
             setvar("#{i+1}", m, :file => file, :line => line, :ephemeral => true)