Escape control characters in std.conv.to error messages

[dlangBugzillaToGithub]

dlang-bugzilla (@CyberShadow) reported this on 2017-07-31T19:31:51Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=17708

CC List

• bugzilla (@WalterBright)
• jrdemail2000-dlang

Description

Currently this program:

///// test.d ////
import std.conv;

void main()
{
    to!int("\r");
}
/////////////////

will produce output which looks like this in a terminal:

' when converting from type string to type intbin/../phobos/std/conv.d(2168): Unexpected '
----------------
??:? pure @safe int std.conv.parse!(int, immutable(char)[]).parse(ref immutable(char)[]) [0x4331de]
??:? pure @safe int std.conv.toImpl!(int, immutable(char)[]).toImpl(immutable(char)[]) [0x436a70]
??:? pure @safe int std.conv.to!(int).to!(immutable(char)[]).to(immutable(char)[]) [0x432a83]
??:? _Dmain [0x432a5d]

The error message appears malformed.

std.conv.to should escape whitespace / control / non-printable characters in its error messages. Perhaps the existing functionality in std.conv / std.format can be reused: format!"%(%s%)"(c.only) will already correctly escape such characters.

See discussion in https://github.com/dlang/phobos/pull/5591 (which fixed this issue specifically for the newline character only) for more details.

[dlangBugzillaToGithub]

jrdemail2000-dlang commented on 2017-12-17T18:50:54Z

Encountered this case in my tools (https://github.com/eBay/tsv-utils-dlang/issues/96). A user was processing a DOS file (with `\r\n` line endings) on a Unix box, byLine left the extraneous `\r` at the end of the line. My tool tried to convert to double, and output the error text when this failed due to the `\r`. The formatting of the output is quite confusing, as `\r` actually repositions to the start of the line, effectively deleting the initial part of the output line. The result:

  ' when converting from type const(char)[] to type doubleUnexpected '

For my tools I'll add explicit detection of DOS line endings on Unix boxes, it's just too common when getting data files from a variety of sources. However, it'd be helpful to update error message generation to handle `\r` and other non-printing characters.

[dlangBugzillaToGithub]

bugzilla (@WalterBright) commented on 2019-12-06T13:10:56Z

Which controll characters need escaping? 0x00 - 0x1F only? Or are there more of them I'm unaware of?