compress object literals (#3546)

3 files changed, 280 insertions, 19 deletions

diff --git a/README.md b/README.md
index 270f20cb..f686889d 100644
--- a/README.md
+++ b/README.md
@@ -478,42 +478,42 @@ if (result.error) throw result.error;
 
 ## Minify options
 
-- `warnings` (default `false`) — pass `true` to return compressor warnings
-  in `result.warnings`. Use the value `"verbose"` for more detailed warnings.
-
-- `parse` (default `{}`) — pass an object if you wish to specify some
-  additional [parse options](#parse-options).
-
 - `compress` (default `{}`) — pass `false` to skip compressing entirely.
   Pass an object to specify custom [compress options](#compress-options).
 
+- `ie8` (default `false`) -- set to `true` to support IE8.
+
+- `keep_fnames` (default: `false`) -- pass `true` to prevent discarding or mangling
+  of function names.  Useful for code relying on `Function.prototype.name`.
+
 - `mangle` (default `true`) — pass `false` to skip mangling names, or pass
   an object to specify [mangle options](#mangle-options) (see below).
 
   - `mangle.properties` (default `false`) — a subcategory of the mangle option.
     Pass an object to specify custom [mangle property options](#mangle-properties-options).
 
+- `nameCache` (default `null`) -- pass an empty object `{}` or a previously
+  used `nameCache` object if you wish to cache mangled variable and
+  property names across multiple invocations of `minify()`. Note: this is
+  a read/write property. `minify()` will read the name cache state of this
+  object and update it during minification so that it may be
+  reused or externally persisted by the user.
+
 - `output` (default `null`) — pass an object if you wish to specify
   additional [output options](#output-options).  The defaults are optimized
   for best compression.
 
-- `sourceMap` (default `false`) - pass an object if you wish to specify
+- `parse` (default `{}`) — pass an object if you wish to specify some
+  additional [parse options](#parse-options).
+
+- `sourceMap` (default `false`) -- pass an object if you wish to specify
   [source map options](#source-map-options).
 
-- `toplevel` (default `false`) - set to `true` if you wish to enable top level
+- `toplevel` (default `false`) -- set to `true` if you wish to enable top level
   variable and function name mangling and to drop unused variables and functions.
 
-- `nameCache` (default `null`) - pass an empty object `{}` or a previously
-  used `nameCache` object if you wish to cache mangled variable and
-  property names across multiple invocations of `minify()`. Note: this is
-  a read/write property. `minify()` will read the name cache state of this
-  object and update it during minification so that it may be
-  reused or externally persisted by the user.
-
-- `ie8` (default `false`) - set to `true` to support IE8.
-
-- `keep_fnames` (default: `false`) - pass `true` to prevent discarding or mangling
-  of function names.  Useful for code relying on `Function.prototype.name`.
+- `warnings` (default `false`) — pass `true` to return compressor warnings
+  in `result.warnings`. Use the value `"verbose"` for more detailed warnings.
 
 ## Minify options structure
 
@@ -682,6 +682,8 @@ If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.u
   where the return value is discarded, to avoid the parens that the
   code generator would insert.
 
+- `objects` (default: `true`) -- compact duplicate keys in object literals.
+
 - `passes` (default: `1`) -- The maximum number of times to run compress.
   In some cases more than one pass leads to further compressed code.  Keep in
   mind more passes will take more time.
diff --git a/lib/compress.js b/lib/compress.js
index 10161337..3058b678 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -74,6 +74,7 @@ function Compressor(options, false_by_default) {
         keep_infinity   : false,
         loops           : !false_by_default,
         negate_iife     : !false_by_default,
+        objects         : !false_by_default,
         passes          : 1,
         properties      : !false_by_default,
         pure_getters    : !false_by_default && "strict",
@@ -6981,6 +6982,41 @@ merge(Compressor.prototype, {
         return self;
     });
 
+    OPT(AST_Object, function(self, compressor) {
+        if (!compressor.option("objects") || compressor.has_directive("use strict")) return self;
+        var props = self.properties;
+        var keys = new Dictionary();
+        var values = [];
+        self.properties.forEach(function(prop) {
+            if (typeof prop.key != "string") {
+                flush();
+                values.push(prop);
+                return;
+            }
+            if (prop.value.has_side_effects(compressor)) {
+                flush();
+            }
+            keys.add(prop.key, prop.value);
+        });
+        flush();
+        if (self.properties.length != values.length) {
+            return make_node(AST_Object, self, {
+                properties: values
+            });
+        }
+        return self;
+
+        function flush() {
+            keys.each(function(expressions, key) {
+                values.push(make_node(AST_ObjectKeyVal, self, {
+                    key: key,
+                    value: make_sequence(self, expressions)
+                }));
+            });
+            keys = new Dictionary();
+        }
+    });
+
     OPT(AST_Return, function(self, compressor) {
         if (self.value && is_undefined(self.value, compressor)) {
             self.value = null;
diff --git a/test/compress/objects.js b/test/compress/objects.js
new file mode 100644
index 00000000..fb1e5865
--- /dev/null
+++ b/test/compress/objects.js
@@ -0,0 +1,223 @@
+duplicate_key: {
+    options = {
+        objects: true,
+        side_effects: true,
+    }
+    input: {
+        var o = {
+            a: 1,
+            b: 2,
+            a: 3,
+        };
+        for (var k in o)
+            console.log(k, o[k]);
+    }
+    expect: {
+        var o = {
+            a: 3,
+            b: 2,
+        };
+        for (var k in o)
+            console.log(k, o[k]);
+    }
+    expect_stdout: [
+        "a 3",
+        "b 2",
+    ]
+}
+
+duplicate_key_strict: {
+    options = {
+        objects: true,
+        side_effects: true,
+    }
+    input: {
+        "use strict";
+        var o = {
+            a: 1,
+            b: 2,
+            a: 3,
+        };
+        for (var k in o)
+            console.log(k, o[k]);
+    }
+    expect: {
+        "use strict";
+        var o = {
+            a: 1,
+            b: 2,
+            a: 3,
+        };
+        for (var k in o)
+            console.log(k, o[k]);
+    }
+    expect_stdout: true
+}
+
+duplicate_key_side_effect: {
+    options = {
+        objects: true,
+        side_effects: true,
+    }
+    input: {
+        var o = {
+            a: 1,
+            b: o = 2,
+            a: 3,
+        };
+        for (var k in o)
+            console.log(k, o[k]);
+    }
+    expect: {
+        var o = {
+            a: 1,
+            b: o = 2,
+            a: 3,
+        };
+        for (var k in o)
+            console.log(k, o[k]);
+    }
+    expect_stdout: [
+        "a 3",
+        "b 2",
+    ]
+}
+
+duplicate_key_with_accessor: {
+    options = {
+        objects: true,
+        side_effects: true,
+    }
+    input: {
+        [
+            {
+                a: 0,
+                b: 1,
+                a: 2,
+                set b(v) {},
+            },
+            {
+                a: 3,
+                b: 4,
+                get a() {
+                    return 5;
+                },
+                a: 6,
+                b: 7,
+                a: 8,
+                b: 9,
+            },
+        ].forEach(function(o) {
+            for (var k in o)
+                console.log(k, o[k]);
+        });
+    }
+    expect: {
+        [
+            {
+                a: 2,
+                b: 1,
+                set b(v) {},
+            },
+            {
+                a: 3,
+                b: 4,
+                get a() {
+                    return 5;
+                },
+                a: 8,
+                b: 9,
+            },
+        ].forEach(function(o) {
+            for (var k in o)
+                console.log(k, o[k]);
+        });
+    }
+    expect_stdout: true
+}
+
+unsafe_object_repeated: {
+    options = {
+        evaluate: true,
+        objects: true,
+        reduce_funcs: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unsafe: true,
+    }
+    input: {
+        var o = { a: { b: 1 }, a: 1 };
+        console.log(
+            o + 1,
+            o.a + 1,
+            o.b + 1,
+            o.a.b + 1
+        );
+    }
+    expect: {
+        var o = { a: 1 };
+        console.log(
+            o + 1,
+            2,
+            o.b + 1,
+            NaN
+        );
+    }
+    expect_stdout: true
+}
+
+numeric_literal: {
+    options = {
+        objects: true,
+        side_effects: true,
+    }
+    mangle = {
+        properties: true,
+    }
+    beautify = {
+        beautify: true,
+    }
+    input: {
+        var obj = {
+            0: 0,
+            "-0": 1,
+            42: 2,
+            "42": 3,
+            0x25: 4,
+            "0x25": 5,
+            1E42: 6,
+            "1E42": 7,
+            "1e+42": 8,
+        };
+        console.log(obj[-0], obj[-""], obj["-0"]);
+        console.log(obj[42], obj["42"]);
+        console.log(obj[0x25], obj["0x25"], obj[37], obj["37"]);
+        console.log(obj[1E42], obj["1E42"], obj["1e+42"]);
+    }
+    expect_exact: [
+        'var obj = {',
+        '    0: 0,',
+        '    "-0": 1,',
+        '    42: 3,',
+        '    37: 4,',
+        '    o: 5,',
+        '    1e42: 8,',
+        '    b: 7',
+        '};',
+        '',
+        'console.log(obj[-0], obj[-""], obj["-0"]);',
+        '',
+        'console.log(obj[42], obj["42"]);',
+        '',
+        'console.log(obj[37], obj["o"], obj[37], obj["37"]);',
+        '',
+        'console.log(obj[1e42], obj["b"], obj["1e+42"]);',
+    ]
+    expect_stdout: [
+        "0 0 1",
+        "3 3",
+        "4 5 4 4",
+        "8 7 8",
+    ]
+}