refactor(dfir_lang): more precise span on generic diagnostics (#2676)

Author: MingweiSamuel

dfir_lang/src/graph/meta_graph.rs

@@ -308,7 +308,7 @@ impl DfirGraph {
                     .contains(&generics.persistence_args.len())
                 {
                     diagnostics.push(Diagnostic::spanned(
-                        generics_span,
+                        generics.persistence_args_span().unwrap_or(generics_span),
                         Level::Error,
                         format!(
                             "`{}` should have {} persistence lifetime arguments, actually has {}.",
@@ -320,7 +320,7 @@ impl DfirGraph {
                 }
                 if !op_constraints.type_args.contains(&generics.type_args.len()) {
                     diagnostics.push(Diagnostic::spanned(
-                        generics_span,
+                        generics.type_args_span().unwrap_or(generics_span),
                         Level::Error,
                         format!(
                             "`{}` should have {} generic type arguments, actually has {}.",

dfir_lang/src/graph/mod.rs

@@ -213,6 +213,45 @@ pub struct OpInstGenerics {
     pub type_args: Vec<Type>,
 }
 
+impl OpInstGenerics {
+    /// Helper to join a sequence of spans into a single span, if possible.
+    ///
+    /// Returns `None` if there are no spans or if any `Span::join` call fails
+    /// (for example, when spans are not contiguous).
+    fn join_spans<I>(mut spans: I) -> Option<Span>
+    where
+        I: Iterator<Item = Span>,
+    {
+        let mut span = spans.next()?;
+        for s in spans {
+            span = span.join(s)?;
+        }
+        Some(span)
+    }
+
+    /// Returns a [`Span`] containing all persistence (lifetime) args if possible.
+    pub fn persistence_args_span(&self) -> Option<Span> {
+        self.generic_args.as_ref().and_then(|args| {
+            Self::join_spans(
+                args.iter()
+                    .filter(|a| matches!(a, GenericArgument::Lifetime(_)))
+                    .map(|a| a.span()),
+            )
+        })
+    }
+
+    /// Returns a [`Span`] containing all type args if possible.
+    pub fn type_args_span(&self) -> Option<Span> {
+        self.generic_args.as_ref().and_then(|args| {
+            Self::join_spans(
+                args.iter()
+                    .filter(|a| matches!(a, GenericArgument::Type(_)))
+                    .map(|a| a.span()),
+            )
+        })
+    }
+}
+
 /// Gets the generic arguments for the operator.
 ///
 /// This helper method is useful due to the special handling of persistence lifetimes (`'static`,

dfir_rs/tests/compile-fail-stable/surface_lattice_fold_wronggeneric.stderr

@@ -1,5 +1,13 @@
 error: `lattice_fold` should have exactly 0 generic type arguments, actually has 1.
- --> tests/compile-fail-stable/surface_lattice_fold_wronggeneric.rs:6:31
+ --> tests/compile-fail-stable/surface_lattice_fold_wronggeneric.rs:7:40
   |
-6 | ...   -> lattice_fold::<'static, dfir_rs::lattices::set_union::SetUnionHashSet<u32>>(dfir_rs::lattices::set_union::SetUnionHashSet::<u32>...
-  |                         ^^^^^^^
+7 |             -> lattice_fold::<'static, SetUnionHashSet<u32>>(SetUnionHashSet::<u32>::default())
+  |                                        ^^^^^^^^^^^^^^^
+
+warning: unused import: `dfir_rs::lattices::set_union::SetUnionHashSet`
+ --> tests/compile-fail-stable/surface_lattice_fold_wronggeneric.rs:2:5
+  |
+2 | use dfir_rs::lattices::set_union::SetUnionHashSet;
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

dfir_rs/tests/compile-fail-stable/surface_lattice_reduce_wronggeneric.stderr

@@ -1,5 +1,13 @@
 error: `lattice_reduce` should have exactly 0 generic type arguments, actually has 1.
- --> tests/compile-fail-stable/surface_lattice_reduce_wronggeneric.rs:6:33
+ --> tests/compile-fail-stable/surface_lattice_reduce_wronggeneric.rs:7:42
   |
-6 |             -> lattice_reduce::<'static, dfir_rs::lattices::set_union::SetUnionHashSet<u32>>()
-  |                                 ^^^^^^^
+7 |             -> lattice_reduce::<'static, SetUnionHashSet<u32>>()
+  |                                          ^^^^^^^^^^^^^^^
+
+warning: unused import: `dfir_rs::lattices::set_union::SetUnionHashSet`
+ --> tests/compile-fail-stable/surface_lattice_reduce_wronggeneric.rs:2:5
+  |
+2 | use dfir_rs::lattices::set_union::SetUnionHashSet;
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

dfir_rs/tests/compile-fail/surface_lattice_fold_wronggeneric.rs

@@ -1,9 +1,10 @@
 use dfir_rs::dfir_syntax;
+use dfir_rs::lattices::set_union::SetUnionHashSet;
 
 fn main() {
     let mut df = dfir_syntax! {
         source_iter([1,2,3,4,5])
-            -> lattice_fold::<'static, dfir_rs::lattices::set_union::SetUnionHashSet<u32>>(dfir_rs::lattices::set_union::SetUnionHashSet::<u32>::default())
+            -> lattice_fold::<'static, SetUnionHashSet<u32>>(SetUnionHashSet::<u32>::default())
             -> for_each(|x| println!("Least upper bound: {:?}", x));
     };
     df.run_available_sync();

dfir_rs/tests/compile-fail/surface_lattice_fold_wronggeneric.stderr

@@ -1,9 +1,10 @@
 use dfir_rs::dfir_syntax;
+use dfir_rs::lattices::set_union::SetUnionHashSet;
 
 fn main() {
     let mut df = dfir_syntax! {
         source_iter([1,2,3,4,5])
-            -> lattice_reduce::<'static, dfir_rs::lattices::set_union::SetUnionHashSet<u32>>()
+            -> lattice_reduce::<'static, SetUnionHashSet<u32>>()
             -> for_each(|x| println!("Least upper bound: {:?}", x));
     };
     df.run_available_sync();