Better disambiguation of leading operators

[odersky]

Classify something as a leading operator only if it is not followed in turn
by an operator. This means that

acc += (i * `i'`)
`i'` += 1

the i' is no longer classified as a leading operator.

[catap]

Hey,

Are you sure that it is related to this issue?

I feel that it introduces another one similar to this: #7031 / #7024

[odersky]

This issue is interesting. It worked somewhat by accident before. First, if the backticked "`a`" gets changed to "a" this never compiles. We do not skip a newline after a prefix operator, so we have a prefix operator + with nothing that follows it --> error. What happened previously was that the "`a`" was interpreted as a leading infix operator, so the lexical analyzer saw a noun +, followed by an operator "`a`", and did not insert a new line. Then the parser made different sense of it and reclassified + to a prefix operator and "`a`" to its operand. But now we do not interpret "`a`" as a leading operator anymore, so we get an error (as we should).

[catap]

I see.

I've also plaid a bit this with scala 2 and can't compile it.

[som-snytt]

Aha. I stared at that test while bringing -Xsource:3 into better alignment. Thanks!

[liufengyun]

LGTM