config: add fallback output mode

toml-config/src/config/parsers/fallback_output_mode.rs

@@ -0,0 +1,38 @@
+use {
+    crate::{
+        config::parser::{DataType, ParseResult, Parser, UnexpectedDataType},
+        toml::toml_span::{Span, SpannedExt},
+    },
+    jay_config::input::FallbackOutputMode,
+    thiserror::Error,
+};
+
+pub struct FallbackOutputModeParser;
+
+#[derive(Debug, Error)]
+pub enum FallbackOutputModeParserError {
+    #[error(transparent)]
+    DataType(#[from] UnexpectedDataType),
+    #[error("Unknown mode {0}")]
+    Unknown(String),
+}
+
+impl Parser for FallbackOutputModeParser {
+    type Value = FallbackOutputMode;
+    type Error = FallbackOutputModeParserError;
+    const EXPECTED: &'static [DataType] = &[DataType::String];
+
+    fn parse_string(&mut self, span: Span, string: &str) -> ParseResult<Self> {
+        use FallbackOutputMode::*;
+        let api = match string.to_ascii_lowercase().as_str() {
+            "cursor" => Cursor,
+            "focus" => Focus,
+            _ => {
+                return Err(
+                    FallbackOutputModeParserError::Unknown(string.to_string()).spanned(span)
+                );
+            }
+        };
+        Ok(api)
+    }
+}