add checker

third_party/move/move-compiler-v2/src/pipeline/unused_assignment_checker.rs

@@ -0,0 +1,78 @@
+// Copyright © Aptos Foundation
+// SPDX-License-Identifier: Apache-2.0
+
+//! Implements a pipeline that checks and gives warning on unused assignments.
+//! Prerequisite: live variable annotation.
+//! Side effect: the `LiveVarAnnotation` will be added to the function target annotations.
+
+use crate::pipeline::livevar_analysis_processor::LiveVarAnnotation;
+use codespan_reporting::diagnostic::Severity;
+use move_binary_format::file_format::CodeOffset;
+use move_model::{ast::TempIndex, model::FunctionEnv};
+use move_stackless_bytecode::{
+    function_target::{FunctionData, FunctionTarget},
+    function_target_pipeline::{FunctionTargetProcessor, FunctionTargetsHolder},
+    stackless_bytecode::{AttrId, Bytecode},
+};
+
+pub struct UnusedAssignmentChecker {}
+
+impl UnusedAssignmentChecker {
+	/// Check if the assignment to `dst` at offset after the position given by `offset` and `after`.
+	fn check_unused_assignment(target: &FunctionTarget, id: AttrId, offset: CodeOffset, dst: TempIndex, after: bool) {
+		let data = target.data;
+		// only check for user defined variables
+		if let Some(dst_name) = data.local_names.get(&dst) {
+			let live_var_info = target
+			.get_annotations()
+			.get::<LiveVarAnnotation>()
+			.expect("live variable annotation")
+			.get_info_at(offset as u16);
+			let live_var_info = if after {
+				&live_var_info.after
+			} else {
+				&live_var_info.before
+			};
+			let dst_name = dst_name.display(target.func_env.symbol_pool()).to_string();
+			if !dst_name.starts_with("_") && live_var_info.get(&dst).is_none() {
+				let loc = target.get_bytecode_loc(id);
+				target.global_env().diag(Severity::Warning, &loc, &format!("Unused assignment to {}. Consider removing or prefixing with an underscore: `_{}`", dst_name, dst_name));
+			}
+		}
+	}
+}
+
+impl FunctionTargetProcessor for UnusedAssignmentChecker {
+    fn process(
+        &self,
+        _targets: &mut FunctionTargetsHolder,
+        func_env: &FunctionEnv,
+        data: FunctionData,
+        _scc_opt: Option<&[FunctionEnv]>,
+    ) -> FunctionData {
+        if func_env.is_native() {
+            return data;
+        }
+        let target = FunctionTarget::new(func_env, &data);
+        for (offset, bytecode) in data.code.iter().enumerate() {
+			let offset = offset as u16;
+            use Bytecode::*;
+            match bytecode {
+                Load(id, dst, _) | Assign(id, dst, _, _) => {
+					UnusedAssignmentChecker::check_unused_assignment(&target, *id, offset, *dst, true)
+                },
+				Call(id, dsts, _, _, _) => {
+					for dst in dsts {
+						UnusedAssignmentChecker::check_unused_assignment(&target, *id, offset, *dst, true)
+					}
+				}
+                _ => {},
+            }
+        }
+        data
+    }
+
+    fn name(&self) -> String {
+        "UnusedAssignmentChecker".to_string()
+    }
+}