[SR-186] Comments not followed by whitespace can confuse compiler #42808

swift-ci · 2015-12-10T23:13:33Z


Previous ID	SR-186
Radar	None
Original Reporter	somegeekintn (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

Swift 2.1.1, Xcode 7.2

Additional Detail from JIRA


Votes	0
Component/s	Compiler
Labels	Bug, StarterBug
Assignee	jder (JIRA)
Priority	Medium

md5: 7122c4cd48dd86437f4b98b0c6e18b52

relates to:

SR-960 Implement SE-0037: Clarify interaction between comments & operators

Issue Description:

Attempting to compile the following:

let even = false

if /* some comment */!even {
    print("odd")
}

Fails with the following errors:

error: expected expression, var, or let in 'if' condition
                if /* some comment */!even {
                                     ^
error: braced block of statements is an unused closure
                if /* some comment */!even {
                                           ^
error: expression resolves to an unused function
                if /* some comment */!even {

Adding whitespace between the */ and ! compiles fine:

if /* some comment */ !even {

As does removing the NOT without added whitespace:

if /* some comment */even {

Expectation: I would expect the compiler to treat everything between and including the /* */ delimiters to be treated as invisible such that:

if /* some comment */!even {

would appear to the compiler as

if !even {

gribozavr · 2015-12-10T23:58:41Z

Sounds like a simple Lexer/Parser bug.

swift-ci · 2015-12-12T03:53:07Z

Comment by Jesse Rusak (JIRA)

The issue appears to be that the ! is lexed as a postfix operator because the character to the left of it (/) is not whitespace, parens, etc. I have a patch that I believe fixes this; will put up a PR shortly.

swift-ci · 2015-12-12T16:17:20Z

Comment by Jesse Rusak (JIRA)

After looking over the language reference, it seems like comments should be treated as whitespace, rather than as "invisible". At the moment, the code which decides between postfix/prefix/binary operators treats comments as non-whitespace.

Changing this code to treat comments as whitespace could break existing code. For example, the code foo/* */! is currently parsed as a postfix operator. Fixing this bug would break that code.

Worth discussing on the mailing list before making a PR?

gribozavr · 2015-12-12T22:46:54Z

I think it is worth a quick email.

swift-ci · 2015-12-20T20:01:43Z

Comment by Jesse Rusak (JIRA)

I've started a thread on swift-evolution to discuss the questions which were raised by this.

swift-ci · 2015-12-21T02:57:40Z

Comment by Jesse Rusak (JIRA)

I've started a draft patch for this, pending further discussion on swift-evolution.

master...jder:comment-operator-fixes

swift-ci · 2016-03-15T14:14:44Z

Comment by Jesse Rusak (JIRA)

The review for the related swift-evolution proposal concludes today: http://thread.gmane.org/gmane.comp.lang.swift.evolution/9218

swift-ci · 2016-04-03T15:47:07Z

Comment by Jesse Rusak (JIRA)

This has been fixed with this PR: #1732

swift-ci transferred this issue from apple/swift-issues Apr 25, 2022

This issue was closed.

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[SR-186] Comments not followed by whitespace can confuse compiler #42808

[SR-186] Comments not followed by whitespace can confuse compiler #42808

swift-ci commented Dec 10, 2015

gribozavr commented Dec 10, 2015

swift-ci commented Dec 12, 2015

swift-ci commented Dec 12, 2015

gribozavr commented Dec 12, 2015

swift-ci commented Dec 20, 2015

swift-ci commented Dec 21, 2015

swift-ci commented Mar 15, 2016

swift-ci commented Apr 3, 2016