core: Fix check for forward refs by checking for ssa refs instead of block refs

tests/filecheck/parser-printer/graph_region.mlir

@@ -43,13 +43,21 @@ builtin.module {
 
 // -----
 
-// A graph region that refers to a value that is not defined in the module.
+// A graph region that refers to values that are not defined in the module.
+
+// CHECK: values used but not defined: [%1]
 
 builtin.module {
     %0 = "test.termop"(%1) : (i32) -> i32
 }
 
-// CHECK: value %1 was used but not defined
+// -----
+
+// CHECK: values used but not defined: [%1, %2]
+
+builtin.module {
+    %0 = "test.termop"(%1, %2) : (i32, i32) -> i32
+}
 
 // -----
 
@@ -64,20 +72,18 @@ builtin.module {
 
 // -----
 
-// A block defined twice
-
 builtin.module {
     ^blockA:
         "test.op"() : () -> ()
     ^blockA:
         "test.op"() : () -> ()
 }
 
-// CHECK:       /graph_region.mlir:72:4
+// CHECK:       /graph_region.mlir:78:4
 // CHECK-NEXT:      ^blockA:
 // CHECK-NEXT:      ^^^^^^^
 // CHECK-NEXT:      re-declaration of block 'blockA'
 // CHECK-NEXT:  originally declared here:
-// CHECK-NEXT:  /graph_region.mlir:6:4
+// CHECK-NEXT:  /graph_region.mlir:4:4
 // CHECK-NEXT:      ^blockA:
 // CHECK-NEXT:      ^^^^^^^

xdsl/parser/core.py

@@ -145,10 +145,7 @@ def parse_module(self, allow_implicit_module: bool = True) -> ModuleOp:
             value_names = ", ".join(
                 "%" + name for name in self.forward_ssa_references.keys()
             )
-            if len(self.forward_block_references.keys()) > 1:
-                self.raise_error(f"values {value_names} were used but not defined")
-            else:
-                self.raise_error(f"value {value_names} was used but not defined")
+            self.raise_error(f"values used but not defined: [{value_names}]")
 
         return module_op