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

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/impure/db_sqlite.nim b/lib/impure/db_sqlite.nim
index 1638d38c6..f79e87f1b 100644
--- a/lib/impure/db_sqlite.nim
+++ b/lib/impure/db_sqlite.nim
@@ -235,7 +235,7 @@ proc tryExec*(db: DbConn, query: SqlQuery,
   assert(not db.isNil, "Database not connected.")
   var q = dbFormat(query, args)
   var stmt: sqlite3.PStmt
-  if prepare_v2(db, q, q.len.cint, stmt, nil) == SQLITE_OK:
+  if prepare_v2(db, q.cstring, q.len.cint, stmt, nil) == SQLITE_OK:
     let x = step(stmt)
     if x in {SQLITE_DONE, SQLITE_ROW}:
       result = finalize(stmt) == SQLITE_OK
@@ -278,7 +278,7 @@ proc setupQuery(db: DbConn, query: SqlQuery,
                 args: varargs[string]): PStmt =
   assert(not db.isNil, "Database not connected.")
   var q = dbFormat(query, args)
-  if prepare_v2(db, q, q.len.cint, result, nil) != SQLITE_OK: dbError(db)
+  if prepare_v2(db, q.cstring, q.len.cint, result, nil) != SQLITE_OK: dbError(db)
 
 proc setupQuery(db: DbConn, stmtName: SqlPrepared): SqlPrepared {.since: (1, 3).} =
   assert(not db.isNil, "Database not connected.")
@@ -653,7 +653,7 @@ proc tryInsertID*(db: DbConn, query: SqlQuery,
   var q = dbFormat(query, args)
   var stmt: sqlite3.PStmt
   result = -1
-  if prepare_v2(db, q, q.len.cint, stmt, nil) == SQLITE_OK:
+  if prepare_v2(db, q.cstring, q.len.cint, stmt, nil) == SQLITE_OK:
     if step(stmt) == SQLITE_DONE:
       result = last_insert_rowid(db)
     if finalize(stmt) != SQLITE_OK: