WIP: diag(naga): refine spans for Select type errors

TODO: This is an improvement. Are there further improvements to make?

TODO: Would these errors look fine with the "overall" span still intact?

Author: ErichDonGubler

naga/src/valid/expression.rs

@@ -53,13 +53,18 @@ pub enum ExpressionError {
         rhs_expr: Handle<crate::Expression>,
         rhs_type: crate::TypeInner,
     },
-    #[error("Expected selection argument types to match, but reject value of type {reject:?} does not match accept value of value {accept:?}")]
+    #[error("Expected selection reject and accept values ({accept:?} and {reject:?}, respectively) to match, but they have different types")]
     SelectValuesTypeMismatch {
-        accept: crate::TypeInner,
-        reject: crate::TypeInner,
+        accept: Handle<crate::Expression>,
+        accept_ty: crate::TypeInner,
+        reject: Handle<crate::Expression>,
+        reject_ty: crate::TypeInner,
+    },
+    #[error("Expected selection condition {actual:?} to be a boolean value")]
+    SelectConditionNotABool {
+        actual: Handle<crate::Expression>,
+        actual_ty: crate::TypeInner,
     },
-    #[error("Expected selection condition to be a boolean value, got {actual:?}")]
-    SelectConditionNotABool { actual: crate::TypeInner },
     #[error("Relational argument {0:?} is not a boolean vector")]
     InvalidBooleanVector(Handle<crate::Expression>),
     #[error("Relational argument {0:?} is not a float")]
@@ -159,8 +164,21 @@ impl ExpressionError {
             Self::IndexableLength(..) => Vec::new(),
             Self::InvalidUnaryOperandType(..) => Vec::new(),
             Self::InvalidBinaryOperandTypes { .. } => Vec::new(),
-            Self::SelectValuesTypeMismatch { .. } => Vec::new(),
-            Self::SelectConditionNotABool { .. } => Vec::new(),
+            Self::SelectValuesTypeMismatch {
+                accept,
+                ref accept_ty,
+                reject,
+                ref reject_ty,
+            } => vec![
+                (accept, format!("accept value of type {accept_ty:?}")),
+                (reject, format!("reject value of type {reject_ty:?}")),
+            ],
+            Self::SelectConditionNotABool {
+                actual,
+                ref actual_ty,
+            } => {
+                vec![(actual, format!("this is of type {actual_ty:?}"))]
+            }
             Self::InvalidBooleanVector(..) => Vec::new(),
             Self::InvalidFloatArgument(..) => Vec::new(),
             Self::Type(..) => Vec::new(),
@@ -1007,13 +1025,16 @@ impl super::Validator {
                 };
                 if accept_inner != reject_inner {
                     return Err(ExpressionError::SelectValuesTypeMismatch {
-                        accept: accept_inner.clone(),
-                        reject: reject_inner.clone(),
+                        accept,
+                        accept_ty: accept_inner.clone(),
+                        reject,
+                        reject_ty: reject_inner.clone(),
                     });
                 }
                 if !condition_good {
                     return Err(ExpressionError::SelectConditionNotABool {
-                        actual: condition_ty.clone(),
+                        actual: condition,
+                        actual_ty: condition_ty.clone(),
                     });
                 }
                 ShaderStages::all()

naga/tests/validation.rs

@@ -644,13 +644,13 @@ fn main() {
 ",
             "\
 error: Entry point main at Compute is invalid
-  ┌─ wgsl:4:9
+  ┌─ wgsl:4:22
   │
 4 │     _ = select(1, 2, 9001);
-  │         ^^^^^^^^^^^^^^^^^^ naga::ir::Expression [3]
+  │                      ^^^^ this is of type Scalar(Scalar { kind: Sint, width: 4 })
   │
   = Expression [3] is invalid
-  = Expected selection condition to be a boolean value, got Scalar(Scalar { kind: Sint, width: 4 })
+  = Expected selection condition [2] to be a boolean value
 
 ",
         ),
@@ -664,13 +664,15 @@ fn main() {
 ",
             "\
 error: Entry point main at Compute is invalid
-  ┌─ wgsl:4:9
+  ┌─ wgsl:4:16
   │
 4 │     _ = select(true, 1, false);
-  │         ^^^^^^^^^^^^^^^^^^^^^^ naga::ir::Expression [3]
+  │                ^^^^  ^ accept value of type Scalar(Scalar { kind: Sint, width: 4 })
+  │                │      
+  │                reject value of type Scalar(Scalar { kind: Bool, width: 1 })
   │
   = Expression [3] is invalid
-  = Expected selection argument types to match, but reject value of type Scalar(Scalar { kind: Bool, width: 1 }) does not match accept value of value Scalar(Scalar { kind: Sint, width: 4 })
+  = Expected selection reject and accept values ([1] and [0], respectively) to match, but they have different types
 
 ",
         ),