fix corner cases in reduce_vars & unused (#5247)

fixes #5246

test/compress/default-values.js

@@ -2038,3 +2038,59 @@ issue_5222: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5246_1: {
+    options = {
+        pure_getters: true,
+        unused: true,
+    }
+    input: {
+        console.log(function({} = 42) {
+            return "PASS";
+        }("foo"));
+    }
+    expect: {
+        console.log(function({} = 0) {
+            return "PASS";
+        }("foo"));
+    }
+    expect_stdout: "PASS"
+    expect_warnings: [
+        "INFO: Dropping unused default argument value {}=42 [test/compress/default-values.js:1,29]",
+        "INFO: Dropping unused default argument value {}=0 [test/compress/default-values.js:1,29]",
+    ]
+    node_version: ">=6"
+}
+
+issue_5246_2: {
+    options = {
+        unused: true,
+    }
+    input: {
+        (function f(a = "FAIL", [] = 42) {
+            console.log(a);
+        })("PASS", []);
+    }
+    expect: {
+        (function(a = "FAIL", []) {
+            console.log(a);
+        })("PASS", []);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5246_3: {
+    options = {
+        default_values: true,
+        unused: true,
+    }
+    input: {
+        console.log(function f([ , {} ] = null){}([ , {} ]));
+    }
+    expect: {
+        console.log(function([ {} ]){}([ {} ]));
+    }
+    expect_stdout: "undefined"
+    node_version: ">=6"
+}

test/compress/rests.js

@@ -359,7 +359,7 @@ retain_funarg_destructured_object_2: {
     expect: {
         console.log(function({ p: a, ... b }) {
             return b;
-        }({ p: "FAIL" }).p || "PASS");
+        }({}).p || "PASS");
     }
     expect_stdout: "PASS"
     node_version: ">=8.3.0"
@@ -1104,7 +1104,7 @@ issue_5108: {
     expect: {
         console.log(function([]) {
             return "PASS";
-        }([ "PASS", "FAIL" ]));
+        }([]));
     }
     expect_stdout: "PASS"
     node_version: ">=6"
@@ -1205,3 +1205,62 @@ issue_5165_2: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5246_1: {
+    options = {
+        reduce_vars: true,
+        rests: true,
+        unused: true,
+    }
+    input: {
+        console.log(typeof function([ , ...a ]) {
+            return this && a;
+        }([ , function(){} ])[0]);
+    }
+    expect: {
+        console.log(typeof function([]) {
+            return this && [ function(){} ];
+        }([])[0]);
+    }
+    expect_stdout: "function"
+    node_version: ">=6"
+}
+
+issue_5246_2: {
+    options = {
+        reduce_vars: true,
+        rests: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        A = [ , "PASS", "FAIL" ];
+        var  [ , ...a ] = [ ... A ];
+        console.log(a[0]);
+    }
+    expect: {
+        A = [ , "PASS", "FAIL" ];
+        var  [ , ...a ] = [ ... A ];
+        console.log(a[0]);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5246_3: {
+    options = {
+        unused: true,
+    }
+    input: {
+        (function f(...[ [ a ] ]) {
+            console.log(a);
+        })([ "PASS" ]);
+    }
+    expect: {
+        (function(...[ a ]) {
+            console.log(a);
+        })([ "PASS" ][0]);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}

test/compress/yields.js

@@ -1371,12 +1371,12 @@ issue_5034: {
     node_version: ">=4"
 }
 
-issue_5076: {
+issue_5076_1: {
     options = {
         evaluate: true,
         hoist_vars: true,
-        passes: 2,
         pure_getters: "strict",
+        sequences: true,
         side_effects: true,
         toplevel: true,
         unused: true,
@@ -1393,13 +1393,41 @@ issue_5076: {
     }
     expect: {
         var a;
-        console.log("PASS");
+        console.log("PASS"),
         a = 42["a"];
     }
     expect_stdout: "PASS"
     node_version: ">=6"
 }
 
+issue_5076_2: {
+    options = {
+        evaluate: true,
+        hoist_vars: true,
+        passes: 2,
+        pure_getters: "strict",
+        sequences: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+        yields: true,
+    }
+    input: {
+        var a;
+        console.log("PASS");
+        var b = function*({
+            p: {},
+        }) {}({
+            p: { a } = 42,
+        });
+    }
+    expect: {
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
 issue_5177: {
     options = {
         properties: true,