git-gui: create a new namespace for chord script evaluation

Evaluating the script in the same namespace as the chord itself creates
potential for variable name collision. And in that case the script would
unknowingly use the chord's variables.

For example, say the script has a variable called 'is_completed', which
also exists in the chord's namespace. The script then calls 'eval' and
sets 'is_completed' to 1 thinking it is setting its own variable,
completely unaware of how the chord works behind the scenes. This leads
to the chord never actually executing because it sees 'is_completed' as
true and thinks it has already completed.

Avoid the potential collision by creating a separate namespace for the
script that is a child of the chord's namespace.

Signed-off-by: Pratyush Yadav <me@yadavpratyush.com>

lib/chord.tcl

@@ -64,6 +64,7 @@ class SimpleChord {
 	field notes
 	field body
 	field is_completed
+	field eval_ns
 
 	# Constructor:
 	#   set chord [SimpleChord::new {body}]
@@ -74,6 +75,7 @@ class SimpleChord {
 		set notes [list]
 		set body $i_body
 		set is_completed 0
+		set eval_ns "[namespace qualifiers $this]::eval"
 		return $this
 	}
 
@@ -83,7 +85,7 @@ class SimpleChord {
 	#     the chord body will be evaluated. This can be used to set variable
 	#     values for the chord body to use.
 	method eval {script} {
-		namespace eval [namespace qualifiers $this] $script
+		namespace eval $eval_ns $script
 	}
 
 	# Method:
@@ -111,7 +113,7 @@ class SimpleChord {
 
 			set is_completed 1
 
-			namespace eval [namespace qualifiers $this] $body
+			namespace eval $eval_ns $body
 			delete_this
 		}
 	}