[Bug rust/20164] fix string printing in rust

[Bug rust/20164] fix string printing in rust

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
Working on the escapes now.

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[Bug rust/20164] fix string printing in rust

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
I wonder if char printing should use unicode-ish syntax like:

(gdb) print 'x'
$1 = U+0078 'x'

Not sure.

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[Bug rust/20164] fix string printing in rust

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mark at klomp dot org

--- Comment #4 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Tom Tromey from comment #3)
> I wonder if char printing should use unicode-ish syntax like:
> 
> (gdb) print 'x'
> $1 = U+0078 'x'
> 
> Not sure.

I like it.

Note that the convention is to have zeros prepended when there are less than 4
digits, but not when there are 5 or 6 digits.
https://www.unicode.org/versions/Unicode14.0.0/appA.pdf
"Leading zeros are omitted, unless the code point would have fewer than four
hexadecimal digits — for example, U+0001, U+0012, U+0123, U+1234, U+12345,
U+102345."

I am not sure how to flag the "illegal" char values, U+D800 to U+DFFF and
anything larger than U+10FFFF. But it would be good to have some indicator you
are dealing with an invalid value.

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[Bug rust/20164] fix string printing in rust

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Mark Wielaard from comment #4)

> I am not sure how to flag the "illegal" char values, U+D800 to U+DFFF and
> anything larger than U+10FFFF. But it would be good to have some indicator
> you are dealing with an invalid value.

You'll already get a hex escape in this situation:

(gdb) p '\u{d800}'
$2 = 55296 '\u{00d800}'

I guess the escapes sort of make the "U+..." idea a bit weird.
It would just be printing the same info twice.

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[Bug rust/20164] fix string printing in rust

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

--- Comment #6 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Tom Tromey from comment #5)
> (In reply to Mark Wielaard from comment #4)
> 
> > I am not sure how to flag the "illegal" char values, U+D800 to U+DFFF and
> > anything larger than U+10FFFF. But it would be good to have some indicator
> > you are dealing with an invalid value.
> 
> You'll already get a hex escape in this situation:
> 
> (gdb) p '\u{d800}'
> $2 = 55296 '\u{00d800}'

But isn't that escape "value" itself invalid?
Shouldn't it be something like

$2 = 55296 '???'

So, use U+xxxxxx 'unicode-char' for valid char values, otherwise "raw number"
'???'

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[Bug rust/20164] fix string printing in rust

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

--- Comment #7 from Tom Tromey <tromey at sourceware dot org> ---
Yeah, I see that rustc rejects a program using that.
We could print something like

$2 = U+D8000 <invalid Unicode character>

... at least if the invalid ranges aren't a pain to figure out.
Is it really just surrogates and values > 0x10ffff?  I didn't look yet.

There are still characters that print as escapes, for example U+200C.
But maybe double-printing these oddities isn't so bad.

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[Bug rust/20164] fix string printing in rust

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

--- Comment #8 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Tom Tromey from comment #7)
> Yeah, I see that rustc rejects a program using that.
> We could print something like
> 
> $2 = U+D8000 <invalid Unicode character>

I would like that.

> ... at least if the invalid ranges aren't a pain to figure out.
> Is it really just surrogates and values > 0x10ffff?  I didn't look yet.

It is, see https://doc.rust-lang.org/reference/types/textual.html
"A value of type char is a Unicode scalar value (i.e. a code point that is not
a surrogate), represented as a 32-bit unsigned word in the 0x0000 to 0xD7FF or
0xE000 to 0x10FFFF range. It is immediate Undefined Behavior to create a char
that falls outside this range."

> There are still characters that print as escapes, for example U+200C.
> But maybe double-printing these oddities isn't so bad.

I don't think it is that odd. You could also use ascii escapes
(https://doc.rust-lang.org/reference/tokens.html#ascii-escapes) when possible.

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[Bug rust/20164] fix string printing in rust

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20164

--- Comment #9 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Mark Wielaard from comment #8)
> I don't think it is that odd. You could also use ascii escapes
> (https://doc.rust-lang.org/reference/tokens.html#ascii-escapes) when
> possible.

That's already done, though I see on that page that only up to 0x7f
is supported for char types, so there's a little bug in the output here,
as gdb checks "if (value <= 255)"

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