Add jl_getch(), use it from getpass()

This works around the lack of `getch()` on non-windows platforms, such
that we can use the windows-specific `getpass()` on all platforms.  This
was necessary to prevent breakage from `musl` due to a bad interaction
between `with_fake_pty()` and `getpass()`.

Author: staticfloat

base/util.jl

@@ -257,19 +257,19 @@ graphical interface.
 """
 function getpass end
 
-if Sys.iswindows()
+_getch() = UInt8(ccall(:jl_getch, Cint, ()))
 function getpass(input::TTY, output::IO, prompt::AbstractString)
     input === stdin || throw(ArgumentError("getpass only works for stdin"))
     print(output, prompt, ": ")
     flush(output)
     s = SecretBuffer()
     plen = 0
     while true
-        c = UInt8(ccall(:_getch, Cint, ()))
-        if c == 0xff || c == UInt8('\n') || c == UInt8('\r')
+        c = _getch()
+        if c == 0xff || c == UInt8('\n') || c == UInt8('\r') || c == 0x04
             break # EOF or return
         elseif c == 0x00 || c == 0xe0
-            ccall(:_getch, Cint, ()) # ignore function/arrow keys
+            _getch() # ignore function/arrow keys
         elseif c == UInt8('\b') && plen > 0
             plen -= 1 # delete last character on backspace
         elseif !iscntrl(Char(c)) && plen < 128
@@ -278,13 +278,6 @@ function getpass(input::TTY, output::IO, prompt::AbstractString)
     end
     return seekstart(s)
 end
-else
-function getpass(input::TTY, output::IO, prompt::AbstractString)
-    (input === stdin && output === stdout) || throw(ArgumentError("getpass only works for stdin"))
-    msg = string(prompt, ": ")
-    unsafe_SecretBuffer!(ccall(:getpass, Cstring, (Cstring,), msg))
-end
-end
 
 # allow new getpass methods to be defined if stdin has been
 # redirected to some custom stream, e.g. in IJulia.

src/jl_exported_funcs.inc

@@ -199,6 +199,7 @@
     XX(jl_generic_function_def) \
     XX(jl_gensym) \
     XX(jl_getallocationgranularity) \
+    XX(jl_getch) \
     XX(jl_getnameinfo) \
     XX(jl_getpagesize) \
     XX(jl_get_ARCH) \

src/julia.h

@@ -2057,6 +2057,7 @@ extern JL_DLLEXPORT JL_STREAM *JL_STDERR;
 JL_DLLEXPORT JL_STREAM *jl_stdout_stream(void);
 JL_DLLEXPORT JL_STREAM *jl_stdin_stream(void);
 JL_DLLEXPORT JL_STREAM *jl_stderr_stream(void);
+JL_DLLEXPORT int jl_getch(void);
 
 // showing and std streams
 JL_DLLEXPORT void jl_flush_cstdio(void) JL_NOTSAFEPOINT;

src/sys.c

@@ -27,6 +27,9 @@
 #include <sys/mman.h>
 #include <dlfcn.h>
 #include <grp.h>
+
+// For `struct termios`
+#include <termios.h>
 #endif
 
 #ifndef _OS_WINDOWS_
@@ -514,6 +517,31 @@ JL_DLLEXPORT JL_STREAM *jl_stdin_stream(void)  { return JL_STDIN; }
 JL_DLLEXPORT JL_STREAM *jl_stdout_stream(void) { return JL_STDOUT; }
 JL_DLLEXPORT JL_STREAM *jl_stderr_stream(void) { return JL_STDERR; }
 
+// terminal workarounds
+JL_DLLEXPORT int jl_getch(void) JL_NOTSAFEPOINT
+{
+#if defined(_OS_WINDOWS_)
+    // Windows has an actual `_getch()`, use that:
+    return _getch();
+#else
+    // On all other platforms, we do the POSIX terminal manipulation dance
+    char c;
+    int r;
+    struct termios old_termios = {0};
+    struct termios new_termios = {0};
+    if (tcgetattr(0, &old_termios) != 0)
+        return -1;
+    new_termios = old_termios;
+    cfmakeraw(&new_termios);
+    if (tcsetattr(0, TCSADRAIN, &new_termios) != 0)
+        return -1;
+    r = read(0, &c, 1);
+    if (tcsetattr(0, TCSADRAIN, &old_termios) != 0)
+        return -1;
+    return r == 1 ? c : -1;
+#endif
+}
+
 // -- processor native alignment information --
 
 JL_DLLEXPORT void jl_native_alignment(uint_t *int8align, uint_t *int16align, uint_t *int32align,