collapse_vars: fix inlining expr into scope with shadowed var (#1065)

* collapse_vars: fix inlining expr into scope with shadowed var * Fix scope crawl * Update lib/compress/tighten-body.js Co-authored-by: Fábio Santos <fabiosantosart@gmail.com> Co-authored-by: Fábio Santos <fabiosantosart@gmail.com>
terser · Sep 11, 2021 · f8a1f89 · f8a1f89
1 parent 438806d
commit f8a1f89
Show file tree

Hide file tree

Showing 2 changed files with 95 additions and 7 deletions.
diff --git a/lib/compress/tighten-body.js b/lib/compress/tighten-body.js
@@ -321,7 +321,9 @@ export function tighten_body(statements, compressor) {
             // Replace variable with assignment when found
             if (can_replace
                 && !(node instanceof AST_SymbolDeclaration)
-                && lhs.equivalent_to(node)) {
+                && lhs.equivalent_to(node)
+                && !shadows(node.scope, lvalues)
+            ) {
                 if (stop_if_hit) {
                     abort = true;
                     return node;
@@ -369,7 +371,7 @@ export function tighten_body(statements, compressor) {
                 || node instanceof AST_PropAccess
                 && (side_effects || node.expression.may_throw_on_access(compressor))
                 || node instanceof AST_SymbolRef
-                && (lvalues.get(node.name) || side_effects && may_modify(node))
+                && ((lvalues.has(node.name) && lvalues.get(node.name).modified) || side_effects && may_modify(node))
                 || node instanceof AST_VarDef && node.value
                 && (lvalues.has(node.name.name) || side_effects && may_modify(node.name))
                 || (sym = is_lhs(node.left, node))
@@ -442,8 +444,9 @@ export function tighten_body(statements, compressor) {
                 // Locate symbols which may execute code outside of scanning range
                 var lvalues = get_lvalues(candidate);
                 var lhs_local = is_lhs_local(lhs);
-                if (lhs instanceof AST_SymbolRef)
-                    lvalues.set(lhs.name, false);
+                if (lhs instanceof AST_SymbolRef) {
+                    lvalues.set(lhs.name, { def: lhs.definition(), modified: false });
+                }
                 var side_effects = value_has_side_effects(candidate);
                 var replace_all = replace_all_symbols();
                 var may_throw = candidate.may_throw(compressor);
@@ -509,8 +512,9 @@ export function tighten_body(statements, compressor) {
                 return false;
             let cur_scope = def.scope;
             while (cur_scope && cur_scope !== scope) {
-                if (cur_scope.variables.has(def.name))
+                if (cur_scope.variables.has(def.name)) {
                     return true;
+                }
                 cur_scope = cur_scope.parent_scope;
             }
             return false;
@@ -791,8 +795,14 @@ export function tighten_body(statements, compressor) {
                 var sym = node;
                 while (sym instanceof AST_PropAccess)
                     sym = sym.expression;
-                if (sym instanceof AST_SymbolRef || sym instanceof AST_This) {
-                    lvalues.set(sym.name, lvalues.get(sym.name) || is_modified(compressor, tw, node, node, 0));
+                if (sym instanceof AST_SymbolRef) {
+                    const prev = lvalues.get(sym.name);
+                    if (!prev || !prev.modified) {
+                        lvalues.set(sym.name, {
+                            def: sym.definition(),
+                            modified: is_modified(compressor, tw, node, node, 0)
+                        });
+                    }
                 }
             });
             get_rvalue(expr).walk(tw);
@@ -904,6 +914,18 @@ export function tighten_body(statements, compressor) {
             }
             return false;
         }
+
+        function shadows(newScope, lvalues) {
+            for (const {def} of lvalues.values()) {
+                let current = newScope;
+                while (current && current !== def.scope) {
+                    let nested_def = current.variables.get(def.name);
+                    if (nested_def && nested_def !== def) return true;
+                    current = current.parent_scope;
+                }
+            }
+            return false;
+        }
     }
 
     function eliminate_spurious_blocks(statements) {

diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
@@ -6056,3 +6056,69 @@ do_not_place_chain_on_lhs_2: {
         a.d = e;
     }
 }
+
+shadowed_variable: {
+    options = {
+        pure_getters: true,
+        collapse_vars: true,
+        unused: true,
+    }
+    input: {
+        function test(e) {
+            const result = {};
+            const test = e.test;
+
+            {
+                const e = random(test);
+                result.discretized = e
+            }
+
+            return result;
+        }
+    }
+    expect: {
+        function test(e) {
+          const result = {};
+          const test = e.test;
+          {
+            const e = random(test);
+            result.discretized = e;
+          }
+          return result;
+        }
+    }
+}
+
+shadowed_variable_2: {
+    options = {
+        pure_getters: true,
+        collapse_vars: true,
+        unused: true,
+    }
+    input: {
+        function test(e) {
+            const result = {};
+            const test = e.test;
+            {
+                {
+                    result.discretized = random(test);
+                }
+                const e = random();
+                console.log(e);
+            }
+            return result;
+        }
+    }
+    expect: {
+        function test(e) {
+          const result = {};
+          const test = e.test;
+          {
+            result.discretized = random(test);
+            const e = random();
+            console.log(e);
+          }
+          return result;
+        }
+    }
+}