feat(oxc_cfg): add implicit return instruction

crates/oxc_cfg/src/block.rs

@@ -47,6 +47,7 @@ impl Instruction {
 pub enum InstructionKind {
     Unreachable,
     Statement,
+    ImplicitReturn,
     Return(ReturnInstructionKind),
     Break(LabeledInstruction),
     Continue(LabeledInstruction),

crates/oxc_cfg/src/builder/mod.rs

@@ -111,8 +111,12 @@ impl<'a> ControlFlowGraphBuilder<'a> {
         self.push_instruction(InstructionKind::Statement, Some(stmt));
     }
 
-    pub fn push_return(&mut self, kind: ReturnInstructionKind, node: NodeId) {
-        self.push_instruction(InstructionKind::Return(kind), Some(node));
+    pub fn push_return(&mut self, kind: ReturnInstructionKind, node: Option<NodeId>) {
+        self.push_instruction(InstructionKind::Return(kind), node);
+    }
+
+    pub fn push_implicit_return(&mut self) {
+        self.push_instruction(InstructionKind::ImplicitReturn, None);
     }
 
     /// Creates and push a new `BasicBlockId` onto `self.error_path` stack.

crates/oxc_cfg/src/dot.rs

@@ -78,6 +78,7 @@ impl DisplayDot for Instruction {
             InstructionKind::Return(ReturnInstructionKind::ImplicitUndefined) => {
                 "return <implicit undefined>"
             }
+            InstructionKind::ImplicitReturn => "return",
             InstructionKind::Return(ReturnInstructionKind::NotImplicitUndefined) => {
                 "return <value>"
             }

crates/oxc_linter/src/rules/eslint/getter_return.rs

@@ -257,8 +257,10 @@ impl GetterReturn {
                                 match it.kind {
                                     // Throws are classified as returning.
                                     InstructionKind::Return(_) | InstructionKind::Throw => true,
+
                                     // Ignore irrelevant elements.
-                                    InstructionKind::Break(_)
+                                    InstructionKind::ImplicitReturn
+                                    | InstructionKind::Break(_)
                                     | InstructionKind::Continue(_)
                                     | InstructionKind::Iteration(_)
                                     | InstructionKind::Unreachable

crates/oxc_linter/src/rules/react/require_render_return.rs

@@ -127,6 +127,7 @@ fn contains_return_statement(node: &AstNode, ctx: &LintContext) -> bool {
                         return (FoundReturn::No, STOP_WALKING_ON_THIS_PATH);
                     }
                     InstructionKind::Return(ReturnInstructionKind::ImplicitUndefined)
+                    | InstructionKind::ImplicitReturn
                     | InstructionKind::Break(_)
                     | InstructionKind::Continue(_)
                     | InstructionKind::Iteration(_)

crates/oxc_semantic/src/builder.rs

@@ -10,7 +10,7 @@ use rustc_hash::FxHashMap;
 
 use oxc_ast::{ast::*, AstKind, Visit};
 use oxc_cfg::{
-    ControlFlowGraphBuilder, CtxCursor, CtxFlags, EdgeType, ErrorEdgeKind,
+    ControlFlowGraphBuilder, CtxCursor, CtxFlags, EdgeType, ErrorEdgeKind, InstructionKind,
     IterationInstructionKind, ReturnInstructionKind,
 };
 use oxc_diagnostics::OxcDiagnostic;
@@ -1286,7 +1286,7 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
 
         /* cfg */
         control_flow!(self, |cfg| {
-            cfg.push_return(ret_kind, node_id);
+            cfg.push_return(ret_kind, Some(node_id));
             cfg.append_unreachable();
         });
         /* cfg */
@@ -1678,6 +1678,16 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
 
         /* cfg */
         control_flow!(self, |cfg| {
+            let c = cfg.current_basic_block();
+            // If the last is an unreachable instruction, it means there is already a explicit
+            // return or throw statement at the end of function body, we don't need to
+            // insert an implicit return.
+            if !matches!(
+                c.instructions().last().map(|inst| &inst.kind),
+                Some(InstructionKind::Unreachable)
+            ) {
+                cfg.push_implicit_return();
+            }
             cfg.ctx(None).resolve_expect(CtxFlags::FUNCTION);
             cfg.release_error_harness(error_harness);
             cfg.pop_finalization_stack();
@@ -1730,6 +1740,16 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
 
         /* cfg */
         control_flow!(self, |cfg| {
+            let c = cfg.current_basic_block();
+            // If the last is an unreachable instruction, it means there is already a explicit
+            // return or throw statement at the end of function body, we don't need to
+            // insert an implicit return.
+            if !matches!(
+                c.instructions().last().map(|inst| &inst.kind),
+                Some(InstructionKind::Unreachable)
+            ) {
+                cfg.push_implicit_return();
+            }
             cfg.ctx(None).resolve_expect(CtxFlags::FUNCTION);
             cfg.release_error_harness(error_harness);
             cfg.pop_finalization_stack();

crates/oxc_semantic/src/dot.rs

@@ -173,6 +173,7 @@ impl DebugDot for Instruction {
             InstructionKind::Return(ReturnInstructionKind::ImplicitUndefined) => {
                 "return <implicit undefined>".to_string()
             }
+            InstructionKind::ImplicitReturn => "return".to_string(),
             InstructionKind::Return(ReturnInstructionKind::NotImplicitUndefined) => {
                 "return <value>".to_string()
             }

crates/oxc_semantic/tests/integration/snapshots/argument_map.snap

@@ -2,6 +2,7 @@
 source: crates/oxc_semantic/tests/integration/cfg.rs
 expression: snapshot
 input_file: crates/oxc_semantic/tests/integration/cfg_fixtures/argument_map.js
+snapshot_kind: text
 ---
 bb0: {
 
@@ -17,6 +18,7 @@ bb2: {
 
 bb3: {
 	statement
+	return
 }
 
 bb4: {
@@ -28,7 +30,8 @@ digraph {
     1 [ label = "bb1" shape = box]
     2 [ label = "bb2" shape = box]
     3 [ label = "bb3
-ExpressionStatement" shape = box]
+ExpressionStatement
+return" shape = box]
     4 [ label = "bb4" shape = box]
     1 -> 0 [ label="Error(Implicit)", style=dashed, color=red]
     3 -> 2 [ label="Error(Implicit)", style=dashed, color=red]

crates/oxc_semantic/tests/integration/snapshots/arrow_expressions.snap

@@ -2,6 +2,7 @@
 source: crates/oxc_semantic/tests/integration/cfg.rs
 expression: snapshot
 input_file: crates/oxc_semantic/tests/integration/cfg_fixtures/arrow_expressions.js
+snapshot_kind: text
 ---
 bb0: {
 
@@ -18,6 +19,7 @@ bb2: {
 
 bb3: {
 	statement
+	return
 }
 
 bb4: {
@@ -26,6 +28,7 @@ bb4: {
 
 bb5: {
 	statement
+	return
 }
 
 digraph {
@@ -35,10 +38,12 @@ ExpressionStatement
 VariableDeclaration" shape = box]
     2 [ label = "bb2" shape = box]
     3 [ label = "bb3
-ExpressionStatement" shape = box]
+ExpressionStatement
+return" shape = box]
     4 [ label = "bb4" shape = box]
     5 [ label = "bb5
-ExpressionStatement" shape = box]
+ExpressionStatement
+return" shape = box]
     1 -> 0 [ label="Error(Implicit)", style=dashed, color=red]
     3 -> 2 [ label="Error(Implicit)", style=dashed, color=red]
     1 -> 3 [ label="NewFunction"]

crates/oxc_semantic/tests/integration/snapshots/class.snap

@@ -2,6 +2,7 @@
 source: crates/oxc_semantic/tests/integration/cfg.rs
 expression: snapshot
 input_file: crates/oxc_semantic/tests/integration/cfg_fixtures/class.js
+snapshot_kind: text
 ---
 bb0: {
 
@@ -17,6 +18,7 @@ bb2: {
 
 bb3: {
 	statement
+	return
 }
 
 bb4: {
@@ -28,7 +30,8 @@ digraph {
     1 [ label = "bb1" shape = box]
     2 [ label = "bb2" shape = box]
     3 [ label = "bb3
-ExpressionStatement" shape = box]
+ExpressionStatement
+return" shape = box]
     4 [ label = "bb4" shape = box]
     1 -> 0 [ label="Error(Implicit)", style=dashed, color=red]
     3 -> 2 [ label="Error(Implicit)", style=dashed, color=red]

crates/oxc_semantic/tests/integration/snapshots/cond_expr_in_arrow_fn.snap

@@ -2,6 +2,7 @@
 source: crates/oxc_semantic/tests/integration/cfg.rs
 expression: snapshot
 input_file: crates/oxc_semantic/tests/integration/cfg_fixtures/cond_expr_in_arrow_fn.js
+snapshot_kind: text
 ---
 bb0: {
 
@@ -32,7 +33,7 @@ bb6: {
 }
 
 bb7: {
-
+	return
 }
 
 digraph {
@@ -46,7 +47,8 @@ ExpressionStatement" shape = box]
 Condition(CallExpression(a))" shape = box]
     5 [ label = "bb5" shape = box]
     6 [ label = "bb6" shape = box]
-    7 [ label = "bb7" shape = box]
+    7 [ label = "bb7
+return" shape = box]
     1 -> 0 [ label="Error(Implicit)", style=dashed, color=red]
     3 -> 2 [ label="Error(Implicit)", style=dashed, color=red]
     1 -> 3 [ label="NewFunction"]

crates/oxc_semantic/tests/integration/snapshots/do_while_break.snap

@@ -2,6 +2,7 @@
 source: crates/oxc_semantic/tests/integration/cfg.rs
 expression: snapshot
 input_file: crates/oxc_semantic/tests/integration/cfg_fixtures/do_while_break.js
+snapshot_kind: text
 ---
 bb0: {
 
@@ -50,7 +51,7 @@ bb10: {
 }
 
 bb11: {
-
+	return
 }
 
 bb12: {
@@ -78,7 +79,8 @@ unreachable" shape = box]
     9 [ label = "bb9
 Condition(true)" shape = box]
     10 [ label = "bb10" shape = box]
-    11 [ label = "bb11" shape = box]
+    11 [ label = "bb11
+return" shape = box]
     12 [ label = "bb12" shape = box]
     1 -> 0 [ label="Error(Implicit)", style=dashed, color=red]
     3 -> 2 [ label="Error(Implicit)", style=dashed, color=red]

crates/oxc_semantic/tests/integration/snapshots/for_in.snap

@@ -2,6 +2,7 @@
 source: crates/oxc_semantic/tests/integration/cfg.rs
 expression: snapshot
 input_file: crates/oxc_semantic/tests/integration/cfg_fixtures/for_in.js
+snapshot_kind: text
 ---
 bb0: {
 
@@ -34,6 +35,7 @@ bb6: {
 
 bb7: {
 	statement
+	return
 }
 
 bb8: {
@@ -53,7 +55,8 @@ Condition(test)" shape = box]
     6 [ label = "bb6
 ExpressionStatement" shape = box]
     7 [ label = "bb7
-ExpressionStatement" shape = box]
+ExpressionStatement
+return" shape = box]
     8 [ label = "bb8" shape = box]
     1 -> 0 [ label="Error(Implicit)", style=dashed, color=red]
     3 -> 2 [ label="Error(Implicit)", style=dashed, color=red]