make implicit cstring conversions explicit (#19488)

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

6 files changed, 22 insertions, 22 deletions

diff --git a/lib/pure/logging.nim b/lib/pure/logging.nim
index 6751a372a..cbe8a827a 100644
--- a/lib/pure/logging.nim
+++ b/lib/pure/logging.nim
@@ -367,7 +367,7 @@ method log*(logger: ConsoleLogger, level: Level, args: varargs[string, `$`]) =
   if level >= logging.level and level >= logger.levelThreshold:
     let ln = substituteLog(logger.fmtStr, level, args)
     when defined(js):
-      let cln: cstring = ln
+      let cln = ln.cstring
       case level
       of lvlDebug: {.emit: "console.debug(`cln`);".}
       of lvlInfo:  {.emit: "console.info(`cln`);".}
diff --git a/lib/pure/nativesockets.nim b/lib/pure/nativesockets.nim
index 39438a04e..ca4e61621 100644
--- a/lib/pure/nativesockets.nim
+++ b/lib/pure/nativesockets.nim
@@ -300,7 +300,7 @@ proc getAddrInfo*(address: string, port: Port, domain: Domain = AF_INET,
     if domain == AF_INET6:
       hints.ai_flags = AI_V4MAPPED
   let socketPort = if sockType == SOCK_RAW: "" else: $port
-  var gaiResult = getaddrinfo(address, socketPort, addr(hints), result)
+  var gaiResult = getaddrinfo(address, socketPort.cstring, addr(hints), result)
   if gaiResult != 0'i32:
     when useWinVersion or defined(freertos):
       raiseOSError(osLastError())
@@ -460,10 +460,10 @@ when not useNimNetLite:
     const size = 256
     result = newString(size)
     when useWinVersion:
-      let success = winlean.gethostname(result, size)
+      let success = winlean.gethostname(result.cstring, size)
     else:
       # Posix
-      let success = posix.gethostname(result, size)
+      let success = posix.gethostname(result.cstring, size)
     if success != 0.cint:
       raiseOSError(osLastError())
     let x = len(cstring(result))
diff --git a/lib/pure/net.nim b/lib/pure/net.nim
index 370b83e54..7b50b8ba6 100644
--- a/lib/pure/net.nim
+++ b/lib/pure/net.nim
@@ -682,7 +682,7 @@ when defineSsl:
           var found = false
           let useEnvVars = (if verifyMode == CVerifyPeerUseEnvVars: true else: false)
           for fn in scanSSLCertificates(useEnvVars = useEnvVars):
-            if newCTX.SSL_CTX_load_verify_locations(fn, nil) == VerifySuccess:
+            if newCTX.SSL_CTX_load_verify_locations(fn.cstring, nil) == VerifySuccess:
               found = true
               break
           if not found:
diff --git a/lib/pure/os.nim b/lib/pure/os.nim
index 79f9950a7..82ccd9051 100644
--- a/lib/pure/os.nim
+++ b/lib/pure/os.nim
@@ -1259,12 +1259,12 @@ proc findExe*(exe: string, followSymlinks: bool = true;
           while followSymlinks: # doubles as if here
             if x.symlinkExists:
               var r = newString(maxSymlinkLen)
-              var len = readlink(x, r, maxSymlinkLen)
+              var len = readlink(x.cstring, r.cstring, maxSymlinkLen)
               if len < 0:
                 raiseOSError(osLastError(), exe)
               if len > maxSymlinkLen:
                 r = newString(len+1)
-                len = readlink(x, r, len)
+                len = readlink(x.cstring, r.cstring, len)
               setLen(r, len)
               if isAbsolute(r):
                 x = r
@@ -1404,8 +1404,8 @@ when not defined(nimscript):
       var bufsize = 1024 # should be enough
       result = newString(bufsize)
       while true:
-        if getcwd(result, bufsize) != nil:
-          setLen(result, c_strlen(result))
+        if getcwd(result.cstring, bufsize) != nil:
+          setLen(result, c_strlen(result.cstring))
           break
         else:
           let err = osLastError()
@@ -1774,12 +1774,12 @@ proc expandSymlink*(symlinkPath: string): string {.noWeirdTarget.} =
     result = symlinkPath
   else:
     result = newString(maxSymlinkLen)
-    var len = readlink(symlinkPath, result, maxSymlinkLen)
+    var len = readlink(symlinkPath, result.cstring, maxSymlinkLen)
     if len < 0:
       raiseOSError(osLastError(), symlinkPath)
     if len > maxSymlinkLen:
       result = newString(len+1)
-      len = readlink(symlinkPath, result, len)
+      len = readlink(symlinkPath, result.cstring, len)
     setLen(result, len)
 
 const hasCCopyfile = defined(osx) and not defined(nimLegacyCopyFile)
@@ -2344,7 +2344,7 @@ iterator walkDir*(dir: string; relative = false, checkDir = false):
             var k = pcFile
 
             template kSetGeneric() =  # pure Posix component `k` resolution
-              if lstat(path, s) < 0'i32: continue  # don't yield
+              if lstat(path.cstring, s) < 0'i32: continue  # don't yield
               elif S_ISDIR(s.st_mode):
                 k = pcDir
               elif S_ISLNK(s.st_mode):
@@ -3041,10 +3041,10 @@ when not weirdTarget and (defined(freebsd) or defined(dragonfly) or defined(netb
 when not weirdTarget and (defined(linux) or defined(solaris) or defined(bsd) or defined(aix)):
   proc getApplAux(procPath: string): string =
     result = newString(maxSymlinkLen)
-    var len = readlink(procPath, result, maxSymlinkLen)
+    var len = readlink(procPath, result.cstring, maxSymlinkLen)
     if len > maxSymlinkLen:
       result = newString(len+1)
-      len = readlink(procPath, result, len)
+      len = readlink(procPath, result.cstring, len)
     setLen(result, len)
 
 when not weirdTarget and defined(openbsd):
@@ -3169,7 +3169,7 @@ proc getAppFilename*(): string {.rtl, extern: "nos$1", tags: [ReadIOEffect], noW
     var size = cuint32(0)
     getExecPath1(nil, size)
     result = newString(int(size))
-    if getExecPath2(result, size):
+    if getExecPath2(result.cstring, size):
       result = "" # error!
     if result.len > 0:
       result = result.expandFilename
diff --git a/lib/pure/osproc.nim b/lib/pure/osproc.nim
index 666ccdda8..a0079cf95 100644
--- a/lib/pure/osproc.nim
+++ b/lib/pure/osproc.nim
@@ -1086,9 +1086,9 @@ elif not defined(useNimRtl):
       var pid: Pid
 
       if (poUsePath in data.options):
-        res = posix_spawnp(pid, data.sysCommand, fops, attr, data.sysArgs, data.sysEnv)
+        res = posix_spawnp(pid, data.sysCommand.cstring, fops, attr, data.sysArgs, data.sysEnv)
       else:
-        res = posix_spawn(pid, data.sysCommand, fops, attr, data.sysArgs, data.sysEnv)
+        res = posix_spawn(pid, data.sysCommand.cstring, fops, attr, data.sysArgs, data.sysEnv)
 
       discard posix_spawn_file_actions_destroy(fops)
       discard posix_spawnattr_destroy(attr)
@@ -1174,14 +1174,14 @@ elif not defined(useNimRtl):
         when defined(uClibc) or defined(linux) or defined(haiku):
           # uClibc environment (OpenWrt included) doesn't have the full execvpe
           let exe = findExe(data.sysCommand)
-          discard execve(exe, data.sysArgs, data.sysEnv)
+          discard execve(exe.cstring, data.sysArgs, data.sysEnv)
         else:
           # MacOSX doesn't have execvpe, so we need workaround.
           # On MacOSX we can arrive here only from fork, so this is safe:
           environ = data.sysEnv
-          discard execvp(data.sysCommand, data.sysArgs)
+          discard execvp(data.sysCommand.cstring, data.sysArgs)
       else:
-        discard execve(data.sysCommand, data.sysArgs, data.sysEnv)
+        discard execve(data.sysCommand.cstring, data.sysArgs, data.sysEnv)
 
       startProcessFail(data)
     {.pop.}
diff --git a/lib/pure/parsejson.nim b/lib/pure/parsejson.nim
index c92eac26e..fcbcf8e36 100644
--- a/lib/pure/parsejson.nim
+++ b/lib/pure/parsejson.nim
@@ -221,7 +221,7 @@ proc parseString(my: var JsonParser): TokKind =
           add(my.a, 'u')
         inc(pos, 2)
         var pos2 = pos
-        var r = parseEscapedUTF16(my.buf, pos)
+        var r = parseEscapedUTF16(cstring(my.buf), pos)
         if r < 0:
           my.err = errInvalidToken
           break
@@ -231,7 +231,7 @@ proc parseString(my: var JsonParser): TokKind =
             my.err = errInvalidToken
             break
           inc(pos, 2)
-          var s = parseEscapedUTF16(my.buf, pos)
+          var s = parseEscapedUTF16(cstring(my.buf), pos)
           if (s and 0xfc00) == 0xdc00 and s > 0:
             r = 0x10000 + (((r - 0xd800) shl 10) or (s - 0xdc00))
           else: