No default angle in element_text when using label.theme and title.theme in guide_legend leads to error when setting other parameters

[Henrik-P]

When using guide = guide_legend(...) to change non-angle parameters of label.theme or title.theme, an error is generated due to non-NULL value for angle.

Here are examples trying to set face, without setting angle:

library(ggplot2)                                                                                                                                                       
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +                                                                                               
geom_point() +                                                                                                                                                         
scale_color_discrete(guide = guide_legend(label.theme = element_text(face = "italic")))                                                                                
#> Error in element_grob.element_text(element = label.theme, label = label, : Text element requires non-NULL value for 'angle'.
                                                                                                                                                                       
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +                                                                                               
geom_point() +                                                                                                                                                         
scale_color_discrete(guide = guide_legend(title.theme = element_text(face = "italic")))                                                                                
#> Error in element_grob.element_text(guide$title.theme %||% calc_element("legend.title", : Text element requires non-NULL value for 'angle'.

(reprex inserts an 'empty plot placeholder' here, despite the code above errors...)

Trying to set size, hjust or vjust without setting angle leads to the same error.

To change any non-angle parameters, we need to set angle as well. E.g.:

ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +                                                                                               
geom_point() +                                                                                                                                                         
scale_color_discrete(guide = guide_legend(label.theme = element_text(face = "italic", angle = 0)))                                                                     

---

In contrast, there is no need to explicitly set any of the other NULL arguments in element_text when setting angle only:

ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +                                                                                               
geom_point() +                                                                                                                                                         
scale_color_discrete(guide = guide_legend(                                                                                                                             
label.theme = element_text(angle = -5)))                                                                                                                               

                                                                                                                                                                       
                                                                                                                                                                       
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +                                                                                               
geom_point() +                                                                                                                                                         
scale_color_discrete(guide = guide_legend(                                                                                                                             
title.theme = element_text(angle = 5)))                                                                                                                                

[daniel-barnett]

ggplot2/R/guide-legend.r

Line 330 in 9034d53

title.theme <- guide$title.theme %||% calc_element("legend.title", theme)

ggplot2/R/guide-legend.r

Line 358 in 9034d53

label.theme <- guide$label.theme %||% calc_element("legend.text", theme)

These two lines seem to be the problem. Once you change at least one parameter, guide$title.theme isn't NULL anymore so guide$title.theme$angle will still be NULL when it is used as element$angle here (same applies for label.theme):

ggplot2/R/theme-elements.r

Lines 206 to 209 in 9034d53

	angle <- angle %||% element$angle
	if (is.null(angle)) {
	stop("Text element requires non-NULL value for 'angle'.")
	}

Adding guide$title.theme$angle <- guide$title.theme$angle %||% calc_element("legend.title", theme)$angle on the next line removes the problem, but there's probably a more elegant fix than this.

[clauswilke]

I think the correct fix is to replace lines 206-209 in theme-elements.r with:

angle <- angle %||% element$angle %||% 0

It's reasonable to always assume that if no angle is given then it's zero.

[hadley]

@clauswilke's sounds like the right fix to me. Would anyone like to do a PR?

[clauswilke]

Done.

[lock]

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