[write-fonts] Additional validation for PairPos1

Another check to ensure that all value records report the correct
format.

resources/codegen_inputs/gpos.rs

@@ -201,6 +201,7 @@ table PairPosFormat1 {
     /// of PairPos subtable, ordered by Coverage Index.
     #[count($pair_set_count)]
     #[read_offset_with($value_format1, $value_format2)]
+    #[validate(check_format_consistency)]
     pair_set_offsets: [Offset16<PairSet>],
 }
 

write-fonts/generated/generated_gpos.rs

@@ -953,7 +953,7 @@ impl Validate for PairPosFormat1 {
                 if self.pair_sets.len() > (u16::MAX as usize) {
                     ctx.report("array exceeds max length");
                 }
-                self.pair_sets.validate_impl(ctx);
+                self.check_format_consistency(ctx);
             });
         })
     }

write-fonts/src/tables/gpos.rs

@@ -107,6 +107,27 @@ impl PairPosFormat1 {
             .map(|rec| rec.value_record2.format())
             .unwrap_or(ValueFormat::empty())
     }
+
+    fn check_format_consistency(&self, ctx: &mut ValidationCtx) {
+        let vf1 = self.compute_value_format1();
+        let vf2 = self.compute_value_format2();
+        ctx.in_array(|ctx| {
+            for pairset in &self.pair_sets {
+                ctx.array_item(|ctx| {
+                    ctx.in_field("pair_value_records", |ctx| {
+                        ctx.in_array(|ctx| {
+                            if pairset.pair_value_records.iter().any(|pairset| {
+                                pairset.value_record1.format() != vf1
+                                    || pairset.value_record2.format() != vf2
+                            }) {
+                                ctx.report("all ValueRecords must have same format")
+                            }
+                        })
+                    })
+                })
+            }
+        })
+    }
 }
 
 impl PairPosFormat2 {
@@ -197,6 +218,8 @@ mod tests {
 
     use read_fonts::tables::{gpos as read_gpos, layout::LookupFlag};
 
+    use crate::tables::layout::VariationIndex;
+
     use super::*;
 
     // adapted from/motivated by https://github.com/fonttools/fonttools/issues/471
@@ -312,4 +335,47 @@ mod tests {
         let ppf2 = PairPos::format_2(coverage, class1, class2, class1recs);
         crate::dump_table(&ppf2).unwrap();
     }
+
+    #[test]
+    fn validate_pairpos1() {
+        let coverage: CoverageTable = [1, 2].into_iter().map(GlyphId::new).collect();
+        let good_table = PairPosFormat1::new(
+            coverage.clone(),
+            vec![
+                PairSet::new(vec![PairValueRecord::new(
+                    GlyphId::new(5),
+                    ValueRecord::new().with_x_advance(5),
+                    ValueRecord::new(),
+                )]),
+                PairSet::new(vec![PairValueRecord::new(
+                    GlyphId::new(1),
+                    ValueRecord::new().with_x_advance(42),
+                    ValueRecord::new(),
+                )]),
+            ],
+        );
+
+        let bad_table = PairPosFormat1::new(
+            coverage,
+            vec![
+                PairSet::new(vec![PairValueRecord::new(
+                    GlyphId::new(5),
+                    ValueRecord::new().with_x_advance(5),
+                    ValueRecord::new(),
+                )]),
+                PairSet::new(vec![PairValueRecord::new(
+                    GlyphId::new(1),
+                    //this is a different format, which is not okay
+                    ValueRecord::new().with_x_placement(42),
+                    ValueRecord::new(),
+                )]),
+            ],
+        );
+
+        assert!(crate::dump_table(&good_table).is_ok());
+        assert!(matches!(
+            crate::dump_table(&bad_table),
+            Err(crate::error::Error::ValidationFailed(_))
+        ));
+    }
 }