enhance `unused` (#5064)

6 files changed, 275 insertions, 100 deletions

diff --git a/test/compress/default-values.js b/test/compress/default-values.js
index de5374fa..7b67ed17 100644
--- a/test/compress/default-values.js
+++ b/test/compress/default-values.js
@@ -279,7 +279,7 @@ reduce_array: {
         console.log(a, b, c);
     }
     expect: {
-        var [ , , c = "baz" ] = [ void 0, null ];
+        var [ c = "baz" ] = [];
         console.log("foo", null, c);
     }
     expect_stdout: "foo null baz"
@@ -299,7 +299,7 @@ reduce_object: {
         console.log(a, b, c);
     }
     expect: {
-        var { c = "baz" } = { a: void 0, b: null };
+        var { c = "baz" } = {};
         console.log("foo", null, c);
     }
     expect_stdout: "foo null baz"
@@ -719,7 +719,7 @@ unused_value_var_2: {
         console.log(a);
     }
     expect: {
-        var [ a ] = [ "PASS" ];
+        var a = [ "PASS" ][0];
         console.log(a);
     }
     expect_stdout: "PASS"
@@ -1300,7 +1300,7 @@ issue_4468: {
     expect: {
         (function() {
             var {
-                [console.log("PASS")]: b = 0,
+                [console.log("PASS")]: b,
             } = 0;
         })();
     }
@@ -1743,7 +1743,7 @@ issue_4854: {
         }());
     }
     expect: {
-        console.log(void ([] = "foo"));
+        console.log(void 0);
     }
     expect_stdout: "undefined"
     node_version: ">=6"
diff --git a/test/compress/destructured.js b/test/compress/destructured.js
index 140d48e1..7db2d238 100644
--- a/test/compress/destructured.js
+++ b/test/compress/destructured.js
@@ -1105,7 +1105,7 @@ drop_unused_1: {
             try {
                 throw 42;
             } catch (a) {
-                var [ a ] = [];
+                var a = [][0];
             }
         }
     }
@@ -1138,6 +1138,142 @@ drop_unused_2: {
     node_version: ">=6"
 }
 
+drop_hole: {
+    options = {
+        unused: true,
+    }
+    input: {
+        var [ a ] = [ , ];
+        console.log(a);
+    }
+    expect: {
+        var a = [][0];
+        console.log(a);
+    }
+    expect_stdout: "undefined"
+    node_version: ">=6"
+}
+
+keep_key: {
+    options = {
+        evaluate: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        ({} = {
+            [(console.log("PASS"), 42)]: null,
+        });
+    }
+    expect: {
+        ({} = {
+            [(console.log("PASS"), 42)]: 0,
+        });
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+keep_reference: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = [ {}, 42 ];
+        var [ b, c ] = a;
+        console.log(a[0] === b ? "PASS" : "FAIL");
+    }
+    expect: {
+        var a = [ {}, 42 ];
+        var [ b ] = a;
+        console.log(a[0] === b ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+maintain_position_assign: {
+    options = {
+        unused: true,
+    }
+    input: {
+        console.log(([ , ] = [ , "PASS" ])[1]);
+    }
+    expect: {
+        console.log([ , "PASS" ][1]);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+maintain_position_var: {
+    options = {
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        A = "FAIL";
+        var [ a, b ] = [ A ];
+        console.log(b || "PASS");
+    }
+    expect: {
+        A = "FAIL";
+        var [ , b ] = [ A ];
+        console.log(b || "PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+side_effects_array: {
+    options = {
+        unused: true,
+    }
+    input: {
+        try {
+            var [ a ] = 42;
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            var [ a ] = 42;
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+side_effects_object: {
+    options = {
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = null, b = console, { c } = 42;
+        try {
+            c[a = "PASS"];
+        } catch (e) {
+            console.log(a);
+        }
+    }
+    expect: {
+        var a = null, c = (console, 42["c"]);
+        try {
+            c[a = "PASS"];
+        } catch (e) {
+            console.log(a);
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
 join_vars: {
     options = {
         conditionals: true,
diff --git a/test/compress/evaluate.js b/test/compress/evaluate.js
index 98ce60e8..ed58ce6f 100644
--- a/test/compress/evaluate.js
+++ b/test/compress/evaluate.js
@@ -684,26 +684,47 @@ prototype_function: {
         side_effects: true,
     }
     input: {
-        var a = ({valueOf: 0}) < 1;
-        var b = ({toString: 0}) < 1;
-        var c = ({valueOf: 0}) + "";
-        var d = ({toString: 0}) + "";
-        var e = (({valueOf: 0}) + "")[2];
-        var f = (({toString: 0}) + "")[2];
-        var g = ({valueOf: 0}).valueOf();
-        var h = ({toString: 0}).toString();
-    }
-    expect: {
-        var a = ({valueOf: 0}) < 1;
-        var b = ({toString: 0}) < 1;
-        var c = ({valueOf: 0}) + "";
-        var d = ({toString: 0}) + "";
-        var e = (({valueOf: 0}) + "")[2];
-        var f = (({toString: 0}) + "")[2];
-        var g = 0();
-        var h = 0();
+        function v() {
+            return this.valueOf === v ? "PASS" : "FAIL";
+        }
+        console.log(({ valueOf: v }) < 1);
+        console.log(({ valueOf: v }) + "");
+        console.log((( {valueOf: v }) + "")[2]);
+        console.log(({ valueOf: v }).valueOf());
+        function t() {
+            return this.toString === t ? "PASS" : "FAIL";
+        }
+        console.log(({ toString: t }) < 1);
+        console.log(({ toString: t }) + "");
+        console.log((( {toString: t }) + "")[2]);
+        console.log(({ toString: t }).toString());
     }
-    expect_stdout: true
+    expect: {
+        function v() {
+            return this.valueOf === v ? "PASS" : "FAIL";
+        }
+        console.log(({ valueOf: v }) < 1);
+        console.log(({ valueOf: v }) + "");
+        console.log((( {valueOf: v }) + "")[2]);
+        console.log(({ valueOf: v }).valueOf());
+        function t() {
+            return this.toString === t ? "PASS" : "FAIL";
+        }
+        console.log(({ toString: t }) < 1);
+        console.log(({ toString: t }) + "");
+        console.log((( {toString: t }) + "")[2]);
+        console.log(({ toString: t }).toString());
+    }
+    expect_stdout: [
+        "false",
+        "PASS",
+        "S",
+        "PASS",
+        "false",
+        "PASS",
+        "S",
+        "PASS",
+    ]
 }
 
 call_args: {
diff --git a/test/compress/exports.js b/test/compress/exports.js
index 0917648b..005a93e6 100644
--- a/test/compress/exports.js
+++ b/test/compress/exports.js
@@ -249,7 +249,7 @@ hoist_exports_2: {
         }
     }
     expect: {
-        let e, { foo: a } = 42;
+        let e, a = 42["foo"];
         function f(t, { [e]: o }) {
             t(o, f);
         }
diff --git a/test/compress/rests.js b/test/compress/rests.js
index a22a6b21..6293d58d 100644
--- a/test/compress/rests.js
+++ b/test/compress/rests.js
@@ -244,7 +244,7 @@ retain_destructured_array: {
         console.log.apply(console, b);
     }
     expect: {
-        var [ , ...b ] = [ "FAIL", "PASS", 42 ];
+        var [ ...b ] = [ "PASS", 42 ];
         console.log.apply(console, b);
     }
     expect_stdout: "PASS 42"
@@ -284,7 +284,7 @@ retain_destructured_object_2: {
             console.log(k, b[k]);
     }
     expect: {
-        var { foo: [], ...b } = { foo: [ "FAIL" ], bar: "PASS", baz: 42 };
+        var { foo: {}, ...b } = { foo: 0, bar: "PASS", baz: 42 };
         for (var k in b)
             console.log(k, b[k]);
     }
@@ -407,6 +407,24 @@ drop_unused_call_args_2: {
     node_version: ">=6"
 }
 
+maintain_position: {
+    options = {
+        unused: true,
+    }
+    input: {
+        A = "FAIL";
+        var [ , ...a ] = [ A, "PASS" ];
+        console.log(a[0]);
+    }
+    expect: {
+        A = "FAIL";
+        var [ , ...a ] = [ A, "PASS" ];
+        console.log(a[0]);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
 merge_funarg: {
     options = {
         merge_vars: true,
@@ -723,6 +741,78 @@ issue_4544_2: {
     node_version: ">=6"
 }
 
+issue_4560_1: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = 0;
+        (function(...{
+            [a++]: {},
+        }) {})(2);
+        console.log(a);
+    }
+    expect: {
+        var a = 0;
+        (function(...{
+            [a++]: {},
+        }) {})(2);
+        console.log(a);
+    }
+    expect_stdout: "1"
+    node_version: ">=6"
+}
+
+issue_4560_2: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = 0;
+        (function(...{
+            [a++]: {},
+        }) {})(2);
+        console.log(a);
+    }
+    expect: {
+        var a = 0;
+        (function(...{
+            [a++]: {},
+        }) {})(2);
+        console.log(a);
+    }
+    expect_stdout: "1"
+    node_version: ">=6"
+}
+
+issue_4560_3: {
+    options = {
+        collapse_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = 0, b;
+        [ ...{
+            [a++]: b,
+        } ] = [ "PASS" ];
+        console.log(b);
+    }
+    expect: {
+        var a = 0, b;
+        [ ...{
+            [a++]: b,
+        } ] = [ "PASS" ];
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
 issue_4562: {
     options = {
         evaluate: true,
diff --git a/test/compress/spreads.js b/test/compress/spreads.js
index 7ef118e1..3b1ec461 100644
--- a/test/compress/spreads.js
+++ b/test/compress/spreads.js
@@ -945,78 +945,6 @@ issue_4556: {
     node_version: ">=6"
 }
 
-issue_4560_1: {
-    options = {
-        evaluate: true,
-        reduce_vars: true,
-        toplevel: true,
-    }
-    input: {
-        var a = 0;
-        (function(...{
-            [a++]: {},
-        }) {})(2);
-        console.log(a);
-    }
-    expect: {
-        var a = 0;
-        (function(...{
-            [a++]: {},
-        }) {})(2);
-        console.log(a);
-    }
-    expect_stdout: "1"
-    node_version: ">=6"
-}
-
-issue_4560_2: {
-    options = {
-        reduce_vars: true,
-        toplevel: true,
-        unused: true,
-    }
-    input: {
-        var a = 0;
-        (function(...{
-            [a++]: {},
-        }) {})(2);
-        console.log(a);
-    }
-    expect: {
-        var a = 0;
-        (function(...{
-            [a++]: {},
-        }) {})(2);
-        console.log(a);
-    }
-    expect_stdout: "1"
-    node_version: ">=6"
-}
-
-issue_4560_3: {
-    options = {
-        collapse_vars: true,
-        reduce_vars: true,
-        toplevel: true,
-    }
-    input: {
-        var a = 0, b;
-        [ ...{
-            [a++]: b,
-        } ] = [ "PASS" ];
-        console.log(b);
-    }
-    expect: {
-        var a = 0, b;
-        [ ...{
-            [a++]: b,
-        } ] = [ "PASS" ];
-        console.log(b);
-    }
-    expect_stdout: "PASS"
-    node_version: ">=6"
-}
-
 issue_4614: {
     options = {
         pure_getters: "strict",