[Issue 10755] New: 'has no effect in expression' error for return too with comma operator

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=10755

           Summary: 'has no effect in expression' error for return too
                    with comma operator
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2013-08-04 10:34:27 PDT ---
With dmd 2.064alpha this code gives:

void main() {
    1;
}


test.d(2): Error: long has no effect in expression (1)

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This gives an error, commas are disallowed here:


void main() {
    int[10] a;
    auto x = a[1, 2];
}


test.d(3): Error: only one index allowed to index int[10u]

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This too gives errors:


void main() {
    int[10, 20] a;
}


test.d(2): Error: found ',' when expecting ']'
test.d(2): Error: no identifier for declarator int[10]
test.d(2): Error: semicolon expected, not '20'
test.d(2): Error: found ']' when expecting ';' following statement

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This is disallowed:

void main() {
    int x = 1, 2;
}


test.d(2): Error: no identifier for declarator int
test.d(2): Error: semicolon expected, not '2'

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This gives an error:

void main() {
    int x;
    x = 1, 2;
}

test.d(3): Error: long has no effect in expression (2)

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While this code compiles with no errors nor warnings:


int foo() {
    return 1, 2; // line 2
}
int bar() {
    return foo(), 3; // line 5
}
void main() {
    assert(bar() == 3);
}


Inside bar() there is a call to foo(). foo() is not pure, but inside foo() "1"
is a pure expression (a literal), so for this program I suggest to generate an
error at line 2, and disallow comma syntax at return points, but probably no
warning at line 5:

test.d(2): Error: int has no effect in expression (1)

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This generates an error:

int foo() {
    return 1;
}
void main() {
    int x;
    x = foo(), 2;
}


test.d(6): Error: long has no effect in expression (2)


So maybe it's right to generate an error at line 5 too.

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