fix corner case in string concatenations (#3692)

- migrate de-facto compression to `conditionals` & `strings`

fixes #3689

4 files changed, 129 insertions, 77 deletions

diff --git a/test/compress/arrays.js b/test/compress/arrays.js
index 497e96c4..9569c4fa 100644
--- a/test/compress/arrays.js
+++ b/test/compress/arrays.js
@@ -16,6 +16,7 @@ holes_and_undefined: {
 constant_join: {
     options = {
         evaluate: true,
+        strings: true,
         unsafe: true,
     }
     input: {
@@ -65,6 +66,7 @@ constant_join: {
 constant_join_2: {
     options = {
         evaluate: true,
+        strings: true,
         unsafe: true,
     }
     input: {
@@ -94,9 +96,11 @@ constant_join_2: {
 constant_join_3: {
     options = {
         evaluate: true,
+        strings: true,
         unsafe: true,
     }
     input: {
+        var foo, bar, baz;
         var a = [ null ].join();
         var b = [ , ].join();
         var c = [ , 1, , 3 ].join();
@@ -111,6 +115,7 @@ constant_join_3: {
         var l = [ foo, bar + "baz" ].join("");
     }
     expect: {
+        var foo, bar, baz;
         var a = "";
         var b = "";
         var c = ",1,,3";
diff --git a/test/compress/concat-strings.js b/test/compress/concat-strings.js
index a9957d3d..5e8c512a 100644
--- a/test/compress/concat-strings.js
+++ b/test/compress/concat-strings.js
@@ -26,7 +26,9 @@ concat_1: {
 }
 
 concat_2: {
-    options = {}
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             1 + (2 + 3),
@@ -55,7 +57,9 @@ concat_2: {
 }
 
 concat_3: {
-    options = {}
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             1 + 2 + (3 + 4 + 5),
@@ -84,7 +88,9 @@ concat_3: {
 }
 
 concat_4: {
-    options = {}
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             1 + "2" + (3 + 4 + 5),
@@ -113,7 +119,9 @@ concat_4: {
 }
 
 concat_5: {
-    options = {}
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             "1" + 2 + (3 + 4 + 5),
@@ -142,7 +150,9 @@ concat_5: {
 }
 
 concat_6: {
-    options = {}
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             "1" + "2" + (3 + 4 + 5),
@@ -171,6 +181,9 @@ concat_6: {
 }
 
 concat_7: {
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             "" + 1,
@@ -197,6 +210,9 @@ concat_7: {
 }
 
 concat_8: {
+    options = {
+        strings: true,
+    }
     input: {
         console.log(
             1 + "",
@@ -221,3 +237,20 @@ concat_8: {
     }
     expect_stdout: true
 }
+
+issue_3689: {
+    options = {
+        strings: true,
+    }
+    input: {
+        console.log(function(a) {
+            return a + ("" + (a[0] = 0));
+        }([]));
+    }
+    expect: {
+        console.log(function(a) {
+            return a + ("" + (a[0] = 0));
+        }([]));
+    }
+    expect_stdout: "00"
+}
diff --git a/test/compress/dead-code.js b/test/compress/dead-code.js
index 024d710b..344e1ff9 100644
--- a/test/compress/dead-code.js
+++ b/test/compress/dead-code.js
@@ -830,6 +830,7 @@ issue_3552: {
 unreachable_assign: {
     options = {
         dead_code: true,
+        strings: true,
     }
     input: {
         console.log(A = "P" + (A = "A" + (B = "S" + (A = B = "S"))), A, B);
diff --git a/test/compress/issue-269.js b/test/compress/issue-269.js
index 20b11b0a..2adc5017 100644
--- a/test/compress/issue-269.js
+++ b/test/compress/issue-269.js
@@ -1,98 +1,111 @@
 issue_269_1: {
-	options = {
+    options = {
         unsafe: true,
     }
-	input: {
-		f(
-			String(x),
-			Number(x),
-			Boolean(x),
+    input: {
+        var x = {};
+        console.log(
+            String(x),
+            Number(x),
+            Boolean(x),
 
-			String(),
-			Number(),
-			Boolean()
-		);
-	}
-	expect: {
-		f(
-			x + '', +x, !!x,
-			'', 0, false
-		);
-	}
+            String(),
+            Number(),
+            Boolean()
+        );
+    }
+    expect: {
+        var x = {};
+        console.log(
+            x + "", +x, !!x,
+            "", 0, false
+        );
+    }
+    expect_stdout: true
 }
 
 issue_269_dangers: {
-	options = {
+    options = {
         unsafe: true,
     }
-	input: {
-		f(
-			String(x, x),
-			Number(x, x),
-			Boolean(x, x)
-		);
-	}
-	expect: {
-		f(String(x, x), Number(x, x), Boolean(x, x));
-	}
+    input: {
+        var x = {};
+        console.log(
+            String(x, x),
+            Number(x, x),
+            Boolean(x, x)
+        );
+    }
+    expect: {
+        var x = {};
+        console.log(String(x, x), Number(x, x), Boolean(x, x));
+    }
+    expect_stdout: true
 }
 
 issue_269_in_scope: {
-	options = {
+    options = {
         unsafe: true,
     }
-	input: {
-		var String, Number, Boolean;
-		f(
-			String(x),
-			Number(x, x),
-			Boolean(x)
-		);
-	}
-	expect: {
-		var String, Number, Boolean;
-		f(String(x), Number(x, x), Boolean(x));
-	}
+    input: {
+        var String, Number, Boolean;
+        var x = {};
+        console.log(
+            String(x),
+            Number(x, x),
+            Boolean(x)
+        );
+    }
+    expect: {
+        var String, Number, Boolean;
+        var x = {};
+        console.log(String(x), Number(x, x), Boolean(x));
+    }
+    expect_stdout: true
 }
 
 strings_concat: {
-	options = {
+    options = {
+        strings: true,
         unsafe: true,
     }
-	input: {
-		f(
-			String(x + 'str'),
-			String('str' + x)
-		);
-	}
-	expect: {
-		f(
-			x + 'str',
-			'str' + x
-		);
-	}
+    input: {
+        var x = {};
+        console.log(
+            String(x + "str"),
+            String("str" + x)
+        );
+    }
+    expect: {
+        var x = {};
+        console.log(
+            x + "str",
+            "str" + x
+        );
+    }
+    expect_stdout: true
 }
 
 regexp: {
-	options = {
+    options = {
         evaluate: true,
         unsafe: true,
     }
-	input: {
-		RegExp("foo");
-		RegExp("bar", "ig");
-		RegExp(foo);
-		RegExp("bar", ig);
-		RegExp("should", "fail");
-	}
-	expect: {
-		/foo/;
-		/bar/ig;
-		RegExp(foo);
-		RegExp("bar", ig);
-		RegExp("should", "fail");
-	}
-	expect_warnings: [
-		'WARN: Error converting RegExp("should","fail") [test/compress/issue-269.js:5,2]',
-	]
+    input: {
+        RegExp("foo");
+        RegExp("bar", "ig");
+        RegExp(foo);
+        RegExp("bar", ig);
+        RegExp("should", "fail");
+    }
+    expect: {
+        /foo/;
+        /bar/ig;
+        RegExp(foo);
+        RegExp("bar", ig);
+        RegExp("should", "fail");
+    }
+    expect_warnings: [
+        'WARN: Error converting RegExp("should","fail") [test/compress/issue-269.js:5,8]',
+    ]
 }