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digitalmars.D.bugs - [Issue 6504] New: Regression(2.041): "str" ~ [arr] allows string literal to be modified

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6504

           Summary: Regression(2.041): "str" ~ [arr] allows string literal
                    to be modified
           Product: D
           Version: D1 & D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: clugdbug yahoo.com.au



for (int i=0; i<3; ++i)
{
    char[] x2 = "xxx" ~ ['c'];
    assert(x2[1] == 'x');
    x2[1] = 'q';
}

The assertion fails the second time through the loop.
What happens, is that "xxx" ~ ['c'] becomes a string literal of value "xxxc"
and type char[]. Thus, it is modifiable.

This code passes on 2.040.

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Aug 16 2011
next sibling parent d-bugmail puremagic.com writes:
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This bug was introduced in this commit, which fixed bug 5852.

https://github.com/D-Programming-Language/dmd/commit/5c7c6b51e27d9cd394ddda4f7940cdf9c1610953

This means that "xxx" ~ ['c'] is a string literal of type char[]
(that is, it's a _mutable_ string literal). Either this needs to be changed, or
else a partial fix of bug 2356 needs to be made.

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Aug 16 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |INVALID



21:27:41 PST ---
I'm going to argue this is not a bug.

While "xxx" is immutable, "xxx"~['c'] is mutable. Otherwise, it would be an
error to use it to initialize x2.

Hence, x2 can modify it. Since x2 is a reference to the initializer, not a copy
of it, the initializer is modified.

The spec says that string literals in the source code are immutable, not
incidental string literals in the compiler that result from other operations.

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Jan 31 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |





 I'm going to argue this is not a bug.
 
 While "xxx" is immutable, "xxx"~['c'] is mutable. Otherwise, it would be an
 error to use it to initialize x2.
 
 Hence, x2 can modify it. Since x2 is a reference to the initializer, not a copy
 of it, the initializer is modified.
 
 The spec says that string literals in the source code are immutable, not
 incidental string literals in the compiler that result from other operations.


Reopened, because in every other respect, it behaves as an immutable string
literal.

On Linux, the test case causes a segfault -- it's an attempt to modify an
read-only literal.
On Windows, it's a secret global variable. You can even mark it as pure.
I don't think we can afford to have something so simple causing undefined
behaviour.

Fixing this bug isn't a big deal, btw. Now that I've put an isCtfe flag in
array literals, this case can go back to being an ArrayLiteral without hurting
CTFE performance.

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Feb 01 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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14:05:45 PST ---
I found out it causes the seg fault after posting last night. I don't quite
understand your suggestion. Do you have a fix that can be pulled?

I did try just not constant folding "string"~['c'] and letting that be done at
runtime, but that caused interpret3.d to fail, as it relies on the constant
folder to do that.

So I think that can work if you enhance CTFE to handle the "string"~['c'] case.

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Feb 01 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|nobody puremagic.com        |clugdbug yahoo.com.au





 I found out it causes the seg fault after posting last night. I don't quite
 understand your suggestion. Do you have a fix that can be pulled?


I thought there was an existing pull request, but I was wrong (the closed
pull457 is what I was thinking of, it's closely related but a little
different).

 
 I did try just not constant folding "string"~['c'] and letting that be done at
 runtime, but that caused interpret3.d to fail, as it relies on the constant
 folder to do that.
 
 So I think that can work if you enhance CTFE to handle the "string"~['c'] case.


Yes, I think that I need to create CTFE-specific appender code anyway. It's the
only case left where CTFE makes useless copies of array literals.
I will work on it tonight.

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Feb 02 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=6504




Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/5fd81965b2155abd6c5f8bbfcb9d7b1460a36b87
6504 Regression(2.041): "str" ~ [arr] allows string literal to be modified

(a) Move slicing functions from interpret.c into constfold.c
(b) move existing  string ~ [arr] -> string into interpret.c
(c) create         string ~ [arr] -> [arr]  for non-CTFE functions.
The CTFE slicing functions are used for the conversion, to avoid code
duplication.

Fixes bug 6504.

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Feb 03 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commit pushed to dmd-1.x at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/467cf6687f60dbb4180df036bd0508b9ce408d19
fix issue 6504, fix issue 7419

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Feb 04 2012
prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|                            |FIXED


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Feb 04 2012