Handle spaces in formula variables

[leeper]

margins() chokes on formulae on variable names with spaces in formulae:

> mtcars$"No of Cylinders" <- mtcars$cyl
> margins(lm(mpg ~ `No of Cylinders`, data = mtcars))
Error in parse(text = x) : <text>:1:4: unexpected symbol
1: No of
       ^
> traceback()
11: parse(text = x)
10: all.vars(parse(text = x))
9: FUN(X[[i]], ...)
8: lapply(X = X, FUN = FUN, ...)
7: sapply(names(classes), function(x) all.vars(parse(text = x)))
6: find_terms_in_model(model, variables = variables)
5: marginal_effects.lm(model = model, data = data, variables = variables, 
       type = type, eps = eps, ...)
4: marginal_effects(model = model, data = data, variables = variables, 
       type = type, eps = eps, ...)
3: build_margins(model = model, data = data_list[[i]], variables = variables, 
       type = type, vcov = vcov, vce = vce, iterations = iterations, 
       unit_ses = unit_ses, eps = eps, ...)
2: margins.lm(lm(mpg ~ `No of Cylinders`, data = mtcars))
1: margins(lm(mpg ~ `No of Cylinders`, data = mtcars))

[leeper]

Oops, it's back.

> margins::margins(lm(mpg ~ `No of Cylinders`, data = mtcars))
Error in parse(text = x, keep.source = FALSE) : 
  <text>:1:5: unexpected symbol
1: ~No of
        ^
> traceback()
17: parse(text = x, keep.source = FALSE)
16: eval(parse(text = x, keep.source = FALSE)[[1L]])
15: formula(eval(parse(text = x, keep.source = FALSE)[[1L]]))
14: formula.character(object, env = baseenv())
13: formula(object, env = baseenv())
12: as.formula(new)
11: update.formula(~., paste0("~", x))
10: update(~., paste0("~", x))
9: all.vars(update(~., paste0("~", x)))
8: FUN(X[[i]], ...)
7: lapply(terms, function(x) all.vars(update(~., paste0("~", x))))
6: unlist(lapply(terms, function(x) all.vars(update(~., paste0("~", 
       x)))))
5: unique(unlist(lapply(terms, function(x) all.vars(update(~., paste0("~", 
       x))))))
4: clean_terms(names(classes)[!classes %in% c("factor", "ordered", 
       "logical")])
3: find_terms_in_model(model, variables = variables)
2: margins.lm(lm(mpg ~ `No of Cylinders`, data = mtcars))
1: margins::margins(lm(mpg ~ `No of Cylinders`, data = mtcars))

[leeper]

Fixed (?) again by e140fe9