Only accept iconv implementations with the GNU behavior

deps/build.jl

@@ -2,9 +2,34 @@ using BinDeps
 
 @BinDeps.setup
 
+# Check for an iconv implementation with the GNU (non-POSIX) behavior:
+# EILSEQ is returned when a sequence cannot be converted to target encoding,
+# instead of succeeding and only returning the number of invalid conversions
+# This non-standard behavior is required to allow replacing invalid sequences
+# with a user-defined character. glibc, GNU libiconv and win_iconv behave that way.
+function validate_iconv(n, h)
+    Libdl.dlsym_e(h, "iconv_open") == C_NULL && return false
+
+    cd = ccall((:iconv_open, h), Ptr{Void}, (Cstring, Cstring), "ASCII", "UTF-8")
+    cd == Ptr{Void}(-1) && return false
+
+    s = "café"
+    a = similar(s.data)
+    inbufptr = Ref{Ptr{UInt8}}(pointer(s.data))
+    inbytesleft = Ref{Csize_t}(length(s.data))
+    outbufptr = Ref{Ptr{UInt8}}(pointer(a))
+    outbytesleft = Ref{Csize_t}(length(a))
+    ret = ccall((:iconv, h), Csize_t,
+                (Ptr{Void}, Ptr{Ptr{UInt8}}, Ref{Csize_t}, Ptr{Ptr{UInt8}}, Ref{Csize_t}),
+                cd, inbufptr, inbytesleft, outbufptr, outbytesleft)
+    ccall((:iconv_close, h), Void, (Ptr{Void},), cd) == -1 && return false
+
+    return ret == -1 % Csize_t && Base.Libc.errno() == Base.Libc.EILSEQ
+end
+
 libiconv = library_dependency("libiconv", aliases = ["libc", "iconv"],
                               # Check whether libc provides iconv_open (as on Linux)
-                              validate = (n, h) -> Libdl.dlsym_e(h, "iconv_open") != C_NULL)
+                              validate = validate_iconv)
 
 @windows_only begin
     using WinRPM