[fea-rs] Support more granular control via API

This is a small set of changes to make it easier to manually run the
validate & compile passes, without using the Compiler struct.

fea-rs/src/compile.rs

@@ -44,7 +44,7 @@ mod validate;
 mod variations;
 
 /// Run the validation pass, returning any diagnostics.
-pub(crate) fn validate<V: VariationInfo>(
+pub fn validate<V: VariationInfo>(
     node: &ParseTree,
     glyph_map: &GlyphMap,
     fvar: Option<&V>,
@@ -54,6 +54,29 @@ pub(crate) fn validate<V: VariationInfo>(
     DiagnosticSet::new(ctx.errors, node, usize::MAX)
 }
 
+/// Run the compilation pass.
+///
+/// If successful, returns the [`Compilation`] result, and any warnings.
+pub fn compile<V: VariationInfo, T: FeatureProvider>(
+    tree: &ParseTree,
+    glyph_map: &GlyphMap,
+    var_info: Option<&V>,
+    extra_features: Option<&T>,
+) -> Result<(Compilation, DiagnosticSet), DiagnosticSet> {
+    let mut ctx = CompilationCtx::new(glyph_map, tree.source_map(), var_info, extra_features);
+    ctx.compile(&tree.typed_root());
+    match ctx.build() {
+        Ok((compilation, warnings)) => {
+            let warnings = DiagnosticSet::new(warnings, tree, usize::MAX);
+            Ok((compilation, warnings))
+        }
+        Err(errors) => {
+            let errors = DiagnosticSet::new(errors, tree, usize::MAX);
+            Err(errors)
+        }
+    }
+}
+
 /// A helper function for extracting the glyph order from a UFO
 ///
 /// If the public.glyphOrder key is missing, or the glyphOrder is malformed,

fea-rs/src/compile/compile_ctx.rs

@@ -170,7 +170,7 @@ impl<'a, F: FeatureProvider, V: VariationInfo> CompilationCtx<'a, F, V> {
         self.features.sort_and_dedupe_lookups();
     }
 
-    pub(crate) fn build(&mut self) -> Result<Compilation, Vec<Diagnostic>> {
+    pub(crate) fn build(&mut self) -> Result<(Compilation, Vec<Diagnostic>), Vec<Diagnostic>> {
         if self.errors.iter().any(Diagnostic::is_error) {
             return Err(self.errors.clone());
         }
@@ -237,19 +237,21 @@ impl<'a, F: FeatureProvider, V: VariationInfo> CompilationCtx<'a, F, V> {
             }
         }
 
-        Ok(Compilation {
-            warnings: self.errors.clone(),
-            head: self.tables.head.as_ref().map(|raw| raw.build(None)),
-            hhea: self.tables.hhea.clone(),
-            vhea: self.tables.vhea.clone(),
-            os2: self.tables.os2.as_ref().map(|raw| raw.build()),
-            gdef,
-            base: self.tables.base.as_ref().map(|raw| raw.build()),
-            name: name_builder.build(),
-            stat,
-            gsub,
-            gpos,
-        })
+        Ok((
+            Compilation {
+                head: self.tables.head.as_ref().map(|raw| raw.build(None)),
+                hhea: self.tables.hhea.clone(),
+                vhea: self.tables.vhea.clone(),
+                os2: self.tables.os2.as_ref().map(|raw| raw.build()),
+                gdef,
+                base: self.tables.base.as_ref().map(|raw| raw.build()),
+                name: name_builder.build(),
+                stat,
+                gsub,
+                gpos,
+            },
+            self.errors.clone(),
+        ))
     }
 
     fn run_feature_writer_if_present(&mut self) {

fea-rs/src/compile/compiler.rs

@@ -160,7 +160,7 @@ impl<'a, F: FeatureProvider, V: VariationInfo> Compiler<'a, F, V> {
         let diagnostics = DiagnosticSet::new(messages, &tree, self.max_n_errors);
         print_warnings_return_errors(diagnostics, self.print_warnings, self.max_n_errors)
             .map_err(CompilerError::CompilationFail)?;
-        Ok(ctx.build().unwrap()) // we've taken the errors, so this can't fail
+        Ok(ctx.build().unwrap().0) // we've taken the errors, so this can't fail
     }
 
     /// Compile to a binary font.

fea-rs/src/compile/output.rs

@@ -7,7 +7,7 @@ use write_fonts::{
 
 use super::Opts;
 
-use crate::{Diagnostic, GlyphMap};
+use crate::GlyphMap;
 
 /// The tables generated by this compilation.
 ///
@@ -20,8 +20,6 @@ use crate::{Diagnostic, GlyphMap};
 ///
 /// [`to_binary`]: Compilation::to_binary
 pub struct Compilation {
-    /// Any warnings encountered during parsing or compilation
-    pub warnings: Vec<Diagnostic>,
     /// The `head` table, if one was generated
     pub head: Option<wtables::head::Head>,
     /// The `hhea` table, if one was generated

fea-rs/src/diagnostic.rs

@@ -139,6 +139,11 @@ impl DiagnosticSet {
         self.max_to_print = max_to_print;
     }
 
+    /// Discard any warnings, keeping only errors
+    pub fn discard_warnings(&mut self) {
+        self.messages.retain(|x| x.is_error());
+    }
+
     /// Remove and return any warnings in this set.
     pub fn split_off_warnings(&mut self) -> Option<DiagnosticSet> {
         self.messages.sort_unstable_by_key(|d| d.level);