report global cycle endpoints

compiler/checker/checker.odin

@@ -7088,6 +7088,28 @@ Cycle_Frame :: struct {
 	next_dependency: int,
 }
 
+cycle_global_location :: proc(checker: ^Checker, global_id: hir.Global_Id) -> (name, path: string, line: int) {
+	name = "<unknown>"
+	path = "<unknown>"
+	line = 1
+	index := int(global_id)
+	if global_id == hir.INVALID_GLOBAL || index >= len(checker.module.globals) {
+		return
+	}
+	name = symbol_text(checker, checker.module.globals[global_id].name)
+	if index >= len(checker.ast_module.globals) {
+		return
+	}
+	span := checker.ast_module.globals[global_id].span
+	source_file := source.source_for_span(checker.diagnostics, span)
+	if source_file == nil {
+		return
+	}
+	path = source_file.path
+	line, _ = source.line_and_column(source_file, span.start)
+	return
+}
+
 detect_global_cycles_visit :: proc(checker: ^Checker, global_id: hir.Global_Id, states: []u8) {
 	if states[global_id] == 2 {
 		return
@@ -7120,11 +7142,18 @@ detect_global_cycles_visit :: proc(checker: ^Checker, global_id: hir.Global_Id,
 			continue
 		}
 		if states[dependency] == 1 {
+			start_name, start_path, start_line := cycle_global_location(checker, dependency)
+			end_name, end_path, end_line := cycle_global_location(checker, frame.global)
 			id := source.addf(
 				checker.diagnostics,
 				checker.ast_module.globals[dependency].span,
-				"global initialization cycle involving '%s'",
-				symbol_text(checker, checker.module.globals[dependency].name),
+				"global initialization cycle from '%s' at %s:%d to '%s' at %s:%d",
+				start_name,
+				start_path,
+				start_line,
+				end_name,
+				end_path,
+				end_line,
 			)
 			checker.module.globals[dependency].diagnostic = id
 			checker.module.globals[dependency].problematic = true