add support to specify mangled name (mishoo#5815)

Author: lauriro

README.md

@@ -1029,6 +1029,15 @@ discarded by the compressor as not referenced.
 The safest comments where to place copyright information (or other info that
 needs to be kept in the output) are comments attached to toplevel nodes.
 
+### Specify preferred mangled name in comment annotations
+
+`/*@mangleTo:X*/` or `/*@mangleTo:X*/` comments allow you to choose the name.
+
+```javascript
+(function(one /*#mangleTo:H*/, two /*#mangleTo:i*/) { /*..*/ })(1, 2);
+// results (function(H,i){ /*..*/ )(1,2);
+```
+
 ### The `unsafe` `compress` option
 
 It enables some transformations that *might* break code logic in certain

lib/scope.js

@@ -565,7 +565,13 @@ function next_mangled_name(def, options) {
             scopes.push(scope);
         } while (scope = scope.parent_scope);
     });
-    var name;
+    var comment = def.orig[0].start.comments_after[0]?.value;
+    var preferred_name = comment && /[@#]mangleTo:(.*)/.exec(comment);
+    var name = preferred_name && preferred_name[1];
+    if (name && !names.has(name)) {
+        in_use.set(name, true);
+        return name;
+    }
     for (var i = 0; i < holes.length; i++) {
         name = base54(holes[i]);
         if (names.has(name)) continue;

test/compress/keep_fargs.js

@@ -965,6 +965,20 @@ function_name_mangle: {
     expect_stdout: "function"
 }
 
+function_name_mangle_from_preferred_comment: {
+    options = {
+        keep_fargs: false,
+    }
+    mangle = {}
+    input: {
+        (function(one /*#mangleTo:W*/, two) {
+            console.log(one, two);
+        })(1, 2);
+    }
+    expect_exact: "(function(W,o){console.log(W,o)})(1,2);"
+    expect_stdout: "1 2"
+}
+
 function_name_mangle_ie8: {
     options = {
         keep_fargs: false,