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Function declaration in a block conflicts with global const declaration #1043
Description
Version (complete output of terser -V or specific git commit)
terser 4.8.0
Complete CLI command or minify() options used
./node_modules/.bin/terser asd.js --mangle --compress
terser input
if(true){
function asd(){}
}
const asd = 123;
terser output or error
Parse error at asd.js:8,6
const asd = 123;
^
ERROR: "asd" is redeclared
at js_error (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/parse.js:369:11)
at On.visit (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/scope.js:328:17)
at On._visit (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:1509:24)
at AST_SymbolConst._walk (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:121:24)
at AST_VarDef.call (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:809:23)
at On._visit (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:1513:21)
at AST_VarDef._walk (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:808:24)
at AST_Const.call (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:779:32)
at On._visit (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:1513:21)
at AST_Const._walk (/home/wutll/home/git/rui/main/server/node_modules/terser/lib/ast.js:776:24)
Expected result
The code works, because JS hoisting is not the same thing as a declaration, there is no redeclaration. Terser works fine when the const asd is above the if-block.
Maybe there is an option for this, but I think this should work out of the box by default...
Btw I am aware that this isn't nice code, but this is something dropping out of rollup.
Activity
[-]Function Declaration in a block conflicts with global const. [/-][+]Function declaration in a block conflicts with global const declaration[/+]jridgewell commentedon Sep 19, 2021
Seems to be a parser issue? If I add a
"use strict"directive it works correctly, but without it errors.fabiosantoscode commentedon Sep 25, 2021
The intersection of declaring a function decl in a block, and strict/nonstrict mode, is really weird.
https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-block-level-function-declarations-web-legacy-compatibility-semantics
This shouldn't be a parse error though.
js_erroris called in lib/scope. That error message is a bit misleading though so it should probably be tackled as well.lal12 commentedon Sep 26, 2021
I think in my original use case I also had the error with
"use strict";, but I will try to find out if that really was the case.when 'module' is enabled, assume strict mode when figuring out scopes. …