chore: display nice error if footer variable not set (#471)

src/presentation/builder.rs

@@ -42,7 +42,7 @@ use crate::{
             DisplaySeparator, RunAcquireTerminalSnippet, RunImageSnippet, RunSnippetOperation,
             SnippetExecutionDisabledOperation,
         },
-        footer::{FooterGenerator, FooterVariables},
+        footer::{FooterGenerator, FooterVariables, InvalidFooterTemplateError},
         modals::{IndexBuilder, KeyBindingsModalBuilder},
         separator::RenderSeparator,
     },
@@ -343,12 +343,12 @@ impl<'a> PresentationBuilder<'a> {
 
         {
             let footer_context = &mut self.footer_vars;
-            footer_context.title = metadata.title.clone().unwrap_or_default();
-            footer_context.sub_title = metadata.sub_title.clone().unwrap_or_default();
-            footer_context.location = metadata.location.clone().unwrap_or_default();
-            footer_context.event = metadata.event.clone().unwrap_or_default();
-            footer_context.date = metadata.date.clone().unwrap_or_default();
-            footer_context.author = metadata.author.clone().unwrap_or_default();
+            footer_context.title.clone_from(&metadata.title);
+            footer_context.sub_title.clone_from(&metadata.sub_title);
+            footer_context.location.clone_from(&metadata.location);
+            footer_context.event.clone_from(&metadata.event);
+            footer_context.date.clone_from(&metadata.date);
+            footer_context.author.clone_from(&metadata.author);
         }
 
         self.set_theme(&metadata.theme)?;
@@ -1096,8 +1096,7 @@ impl<'a> PresentationBuilder<'a> {
     }
 
     fn generate_footer(&self) -> Result<Vec<RenderOperation>, BuildError> {
-        let generator = FooterGenerator::new(self.theme.footer.clone(), &self.footer_vars, &self.theme.palette)
-            .map_err(|e| BuildError::InvalidFooter(e.to_string()))?;
+        let generator = FooterGenerator::new(self.theme.footer.clone(), &self.footer_vars, &self.theme.palette)?;
         Ok(vec![
             // Exit any layout we're in so this gets rendered on a default screen size.
             RenderOperation::ExitLayout,
@@ -1294,7 +1293,7 @@ pub enum BuildError {
     PresentationTitle(String),
 
     #[error("invalid footer: {0}")]
-    InvalidFooter(String),
+    InvalidFooter(#[from] InvalidFooterTemplateError),
 }
 
 enum ExecutionMode {

src/ui/footer.rs

@@ -1,8 +1,8 @@
 use crate::{
     markdown::{
         elements::{Line, Text},
-        parse::MarkdownParser,
-        text_style::TextStyle,
+        parse::{MarkdownParser, ParseInlinesError},
+        text_style::{TextStyle, UndefinedPaletteColorError},
     },
     render::{
         operation::{AsRenderOperations, ImageRenderProperties, MarginProperties, RenderOperation},
@@ -19,12 +19,12 @@ use unicode_width::UnicodeWidthStr;
 pub(crate) struct FooterVariables {
     pub(crate) current_slide: usize,
     pub(crate) total_slides: usize,
-    pub(crate) author: String,
-    pub(crate) title: String,
-    pub(crate) sub_title: String,
-    pub(crate) event: String,
-    pub(crate) location: String,
-    pub(crate) date: String,
+    pub(crate) author: Option<String>,
+    pub(crate) title: Option<String>,
+    pub(crate) sub_title: Option<String>,
+    pub(crate) event: Option<String>,
+    pub(crate) location: Option<String>,
+    pub(crate) date: Option<String>,
 }
 
 #[derive(Debug)]
@@ -197,23 +197,23 @@ impl FooterLine {
                 ClosedBrace => Cow::Borrowed("}"),
                 Literal(text) => Cow::Owned(text),
                 TotalSlides => Cow::Owned(total_slides.to_string()),
-                Author => Cow::Borrowed(author.as_str()),
-                Title => Cow::Borrowed(title.as_str()),
-                SubTitle => Cow::Borrowed(sub_title.as_str()),
-                Event => Cow::Borrowed(event.as_str()),
-                Location => Cow::Borrowed(location.as_str()),
-                Date => Cow::Borrowed(date.as_str()),
+                Author => Self::extract_variable("author", author)?,
+                Title => Self::extract_variable("title", title)?,
+                SubTitle => Self::extract_variable("sub_title", sub_title)?,
+                Event => Self::extract_variable("event", event)?,
+                Location => Self::extract_variable("location", location)?,
+                Date => Self::extract_variable("date", date)?,
             };
             if raw_text.lines().count() != 1 {
-                return Err(InvalidFooterTemplateError("footer cannot contain newlines".into()));
+                return Err(InvalidFooterTemplateError::NoNewlines);
             }
             let starting_length = raw_text.len();
             let raw_text = raw_text.trim_start();
             let left_whitespace = starting_length - raw_text.len();
             let raw_text = raw_text.trim_end();
             let right_whitespace = starting_length - raw_text.len() - left_whitespace;
-            let inlines = parser.parse_inlines(raw_text).map_err(|e| InvalidFooterTemplateError(e.to_string()))?;
-            let mut contents = inlines.resolve(palette).map_err(|e| InvalidFooterTemplateError(e.to_string()))?;
+            let inlines = parser.parse_inlines(raw_text)?;
+            let mut contents = inlines.resolve(palette)?;
             if left_whitespace != 0 {
                 contents.0.insert(0, " ".repeat(left_whitespace).into());
             }
@@ -225,6 +225,13 @@ impl FooterLine {
         line.apply_style(style);
         Ok(Self(line))
     }
+
+    fn extract_variable<'a>(
+        name: &'static str,
+        variable: &'a Option<String>,
+    ) -> Result<Cow<'a, str>, InvalidFooterTemplateError> {
+        variable.as_deref().map(Cow::Borrowed).ok_or(InvalidFooterTemplateError::VariableNotSet(name))
+    }
 }
 
 #[derive(Clone, Debug)]
@@ -248,8 +255,19 @@ impl RenderedFooterContent {
 }
 
 #[derive(Debug, thiserror::Error)]
-#[error("invalid footer template: {0}")]
-pub(crate) struct InvalidFooterTemplateError(String);
+pub(crate) enum InvalidFooterTemplateError {
+    #[error("footer cannot contain multiple lines")]
+    NoNewlines,
+
+    #[error("invalid markdown: {0}")]
+    Inlines(#[from] ParseInlinesError),
+
+    #[error(transparent)]
+    PaletteColor(#[from] UndefinedPaletteColorError),
+
+    #[error("variable '{0}' not set")]
+    VariableNotSet(&'static str),
+}
 
 #[cfg(test)]
 mod tests {
@@ -262,12 +280,12 @@ mod tests {
     static VARIABLES: Lazy<FooterVariables> = Lazy::new(|| FooterVariables {
         current_slide: 1,
         total_slides: 5,
-        author: "bob".into(),
-        title: "hi".into(),
-        sub_title: "bye".into(),
-        event: "test".into(),
-        location: "here".into(),
-        date: "now".into(),
+        author: Some("bob".into()),
+        title: Some("hi".into()),
+        sub_title: Some("bye".into()),
+        event: Some("test".into()),
+        location: Some("here".into()),
+        date: Some("now".into()),
     });
 
     static PALETTE: Lazy<ColorPalette> = Lazy::new(|| ColorPalette {