context, vweb: add ability to set and get values on vweb.Context (#18564)

vlib/context/context.v

@@ -65,12 +65,41 @@ pub interface Any {}
 pub interface Context {
 	deadline() ?time.Time
 	value(key Key) ?Any
-	str() string
 mut:
 	done() chan int
 	err() IError
 }
 
+// str returns the `str` method of the corresponding Context struct
+pub fn (ctx &Context) str() string {
+	// since `Context` is an interface we have to manually match every possible
+	// type that implements `Context` if we want to use a `Context` as a field in a struct
+	// since the `Context` interface has to implement its own `str` method.
+	match ctx {
+		BackgroundContext {
+			return ctx.str()
+		}
+		EmptyContext {
+			return ctx.str()
+		}
+		TodoContext {
+			return ctx.str()
+		}
+		CancelContext {
+			return ctx.str()
+		}
+		TimerContext {
+			return ctx.str()
+		}
+		ValueContext {
+			return ctx.str()
+		}
+		else {
+			return context_name(ctx)
+		}
+	}
+}
+
 fn context_name(ctx Context) string {
 	return typeof(ctx)
 }

vlib/context/empty_test.v

@@ -2,7 +2,7 @@ module context
 
 fn test_background() {
 	ctx := background()
-	assert 'context.Background' == ctx.str()
+	assert '&context.Background' == ctx.str()
 	if _ := ctx.value('') {
 		panic('This should never happen')
 	}
@@ -10,7 +10,7 @@ fn test_background() {
 
 fn test_todo() {
 	ctx := todo()
-	assert 'context.TODO' == ctx.str()
+	assert '&context.TODO' == ctx.str()
 	if _ := ctx.value('') {
 		panic('This should never happen')
 	}