The Nim manual says that an implicit conversion to cstring will
eventually not be allowed [1]:
A Nim `string` is implicitly convertible to `cstring` for convenience.
[...]
Even though the conversion is implicit, it is not *safe*: The garbage collector
does not consider a `cstring` to be a root and may collect the underlying
memory. For this reason, the implicit conversion will be removed in future
releases of the Nim compiler. Certain idioms like conversion of a `const` string
to `cstring` are safe and will remain to be allowed.
And from Nim 1.6.0, such a conversion triggers a warning [2]:
A dangerous implicit conversion to `cstring` now triggers a `[CStringConv]` warning.
This warning will become an error in future versions! Use an explicit conversion
like `cstring(x)` in order to silence the warning.
However, some files in this repo produced such a warning. For example,
before this commit, compiling `parsejson.nim` would produce:
/foo/Nim/lib/pure/parsejson.nim(221, 37) Warning: implicit conversion to 'cstring' from a non-const location: my.buf; this will become a compile time error in the future [CStringConv]
/foo/Nim/lib/pure/parsejson.nim(231, 39) Warning: implicit conversion to 'cstring' from a non-const location: my.buf; this will become a compile time error in the future [CStringConv]
This commit resolves the most visible `CStringConv` warnings, making the
cstring conversions explicit.
[1] https://github.com/nim-lang/Nim/blob/d2318d9ccfe6/doc/manual.md#cstring-type
[2] https://github.com/nim-lang/Nim/blob/d2318d9ccfe6/changelogs/changelog_1_6_0.md#type-system
