Duplicate `"use strict"` prologue in the generated output.

[mhegazy]

Duplicate "use strict" prologue in the generated output.

See https://github.com/raw/Microsoft/TypeScript/master/lib/tsc.js

[a-tarasyuk]

@mhegazy @weswigham

TS transformer uses node.prepends, which includes build/local/compiler.js (createInputFiles, node.javascriptText). compiler.js has own "use strict" definition - it is the first "use strict"

The second "use strict" TS transformer adds in the method visitSourceFile because the following condition does not check "use strict" definition in the node.prepends

const alwaysStrict = getStrictOptionValue(compilerOptions, "alwaysStrict") &&
   !(isExternalModule(node) && moduleKind >= ModuleKind.ES2015) &&
   !isJsonSourceFile(node);

as the result, tsc.js contains "use strict";"use strict";

Does that make sense? What do you think?

[weswigham]

Yep, that's exactly the problem. To fix it, we need to instantiate a scanner and scan the first of the prepends to see if it already has a use strict statement.

[weswigham]

Actually, we should scan all of them and remove any prologues we find and unify them/move them to the top. That has interesting implications for souremapping, too.

[a-tarasyuk]

@weswigham thanks.

Actually, we should scan all of them and remove any prologues we find and unify them/move them to the top. That has interesting implications for souremapping, too.

Should we remove prologues from prepends or check if prologues exist in some of them and skip adding "use strict" later? Why I ask, because "compiler.js" has "use strict", and in my opinion, it is right, because "compiler.js" independent file and it should contain "use strict"., just need to skip adding addition prologues later

[weswigham]

@a-tarasyuk Keeping them in the intermediate outputs is fine (heck, we should probably even error if they don't all have the same set of prologues - concating a loose file to a strict one could be bad!) - we just need to remove them when concatenating and fixup the resulting concatenated sourcemaps.

[a-tarasyuk]

@weswigham thanks. For instance, during concatenation, we need to remove "use strict" prologue directly in javascriptText(string representation). is it true? I just want to fix and make PR, if you don't mind. :)

[weswigham]

I don't think we can remove it on load - since we need to track what we remove to update the sourcemap positions - it should probably just be elided during concatenation itself.

[a-tarasyuk]

@weswigham I thought that we could track "use strict"; prologue when the compiler builds prepends - getPrependNodes, however, it is not true.

[weswigham]

Yeah. Instead you wanna create a scanner and scan the text and check the type of the first token.