Merge pull request #887 from googlefonts/fea-rs-verbose-error

[fea-rs] Add CompilerError::display_verbose

fea-rs/src/bin/compile.rs

@@ -6,7 +6,7 @@ use clap::Parser;
 use fea_rs::{
     compile::{
         self,
-        error::{FontGlyphOrderError, GlyphOrderError, UfoGlyphOrderError},
+        error::{CompilerError, FontGlyphOrderError, GlyphOrderError, UfoGlyphOrderError},
         Compiler, MockVariationInfo, NopFeatureProvider, Opts,
     },
     GlyphMap,
@@ -80,8 +80,8 @@ enum Error {
     MissingGlyphOrder,
     #[error("Error parsing axis info: L{line}, '{message}'")]
     BadAxisInfo { line: usize, message: String },
-    #[error("{0}")]
-    CompileFail(#[from] compile::error::CompilerError),
+    #[error("{}", .0.display_verbose())]
+    CompileFail(#[from] CompilerError),
 }
 
 /// Compile FEA files

fea-rs/src/compile/error.rs

@@ -1,5 +1,7 @@
 //! Error types related to compilation
 
+use std::fmt::Display;
+
 use write_fonts::{read::ReadError, BuilderError};
 
 use crate::{parse::SourceLoadError, DiagnosticSet};
@@ -58,6 +60,26 @@ pub enum CompilerError {
     WriteFail(#[from] BuilderError),
 }
 
+impl CompilerError {
+    /// Return a `Display` type that reports the location and nature of syntax errors
+    pub fn display_verbose(&self) -> impl Display + '_ {
+        struct Verbose<'a>(&'a CompilerError);
+        impl std::fmt::Display for Verbose<'_> {
+            fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                write!(f, "{}", self.0)?;
+                let diagnostic = match self.0 {
+                    CompilerError::ParseFail(x)
+                    | CompilerError::ValidationFail(x)
+                    | CompilerError::CompilationFail(x) => x,
+                    _ => return Ok(()),
+                };
+                write!(f, "\n{}", diagnostic.display())
+            }
+        }
+        Verbose(self)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;