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Not possible to compile latest Angular 2 due to literal types #11794
Description
TypeScript Version: nightly (2.1.0-dev.20161022)
Expected behavior:
No compiler errors.
Actual behavior:
› ./node_modules/.bin/tsc --version
Version 2.1.0-dev.20161022
› ./node_modules/.bin/tsc -p ./modules/tsconfig.json
modules/@angular/compiler/src/expression_parser/lexer.ts(296,13): error TS2365: Operator '==' cannot be applied to types '92' and '117'.
It looks like literal type inference went a bit aggressive with this particular piece of code.
Funnily enough, I've tried to isolate the issue in a more concise class with just a scan method but works all the time, so it must be some weird combination of things going on here, which I couldn't figure out. ):
Activity
[-]Not possible to compile latest Angular 2 modules due to literal types[/-][+]Not possible to compile latest Angular 2 due to literal types[/+]alfaproject commentedon Oct 22, 2016
Forgot to say that it is possible to prevent that error by widening the literal type to number, like this:
But still looks like some weird bug to me.
ahejlsberg commentedon Oct 22, 2016
This is an effect of #11587. In the
if (this.peek == chars.$BACKSLASH)test we narrowthis.peekto the literal type92(the value ofchars.$BACKSLASH). We then complain when you try to compare this literal type to the literal type 117 (the value ofchars.$u). The issue of course is that we don't know thatthis.advance()has a side effect on the value ofthis.peek.Interestingly, we had a very similar issue with TypeScript's own parser as described here. We opted to use an accessor function to obtain the value of the side effected variable.