Add option to prevent reversing AST_Binary nodes

[iccir]

Bug report or Feature request?
Feature request

Version (complete output of terser -V or specific git commit) 5.16.6

Complete CLI command or minify() options used

    let results = (await minify(inContents, {
        mangle: false,
        compress: {
            arguments     : false,
            arrows        : false,
            booleans      : false,
            booleans_as_integers : false,
            collapse_vars : false,
            comparisons   : false,
            computed_props: false,
            conditionals  : false,
            dead_code     : false,
            defaults      : false,
            directives    : false,
            drop_console  : false,
            drop_debugger : false,
            evaluate      : false,
            expression    : false,
            global_defs   : false,
            hoist_funs    : false,
            hoist_props   : false,
            hoist_vars    : false,
            ie8           : false,
            if_return     : false,
            inline        : false,
            join_vars     : false,
            keep_classnames: false,
            keep_fargs    : false,
            keep_fnames   : false,
            keep_infinity : false,
            loops         : false,
            module        : false,
            negate_iife   : false,
            passes        : 1,
            properties    : false,
            pure_getters  : false,
            pure_funcs    : null,
            reduce_funcs  : false,
            reduce_vars   : false,
            sequences     : false,
            side_effects  : false,
            switches      : false,
            top_retain    : null,
            typeofs       : false,
            unsafe        : false,
            unsafe_arrows : false,
            unsafe_comps  : false,
            unsafe_Function: false,
            unsafe_math   : false,
            unsafe_symbols: false,
            unsafe_methods: false,
            unsafe_proto  : false,
            unsafe_regexp : false,
            unsafe_undefined: false,
            unused        : false,
            warnings      : false  // legacy
        },
        output: {
            beautify: true
        }
    })).code;

terser input
if (foo == 42) { bar(); }

terser output or error
if (42 == foo) bar()

Expected result
if (foo == 42) bar()

Notes
Right now, if you turn on compress, there is no way of opting-out of AST_Binary's reversible()/reverse() logic, even when comparisons is set to false. Could there be a new option to prevent this, or could the comparisons option prevent reversing.

Specifically, in our use case, we need to run with compress for dead_code and unused, but we want to prevent as many additional transformations as possible.

[iccir]

Upon further investigation, the fix involves adding an option check to Line 2134 of lib/compress/index.js.

I believe that the default value of this option needs to be true rather than !false_by_default, as too many test cases expect constants to be moved to the left-hand side.

[fabiosantoscode]

Hello!

As an unrelated hint, you can set defaults: false in the compressor and only enable what you need, avoiding that big options object.

Would you be open to issuing a PR for this?

[iccir]

Thanks for the hint about defaults: false, I didn't realize that was API.

I think the "move constants to left-hand side" option should be disabled with defaults: false, even though it means auditing all of the failing test cases. Let me investigate and I'll issue a PR!

[iccir]

In version 5.16.9.