allow prompt and getpass to dispatch on the input-stream type (#28038)

* allow prompt and getpass to dispatch on the input-stream type

* dispatch on both stdin and stdout

* tests

* test default arg of Base.prompt

base/util.jl

@@ -458,9 +458,10 @@ graphical interface.
 function getpass end
 
 if Sys.iswindows()
-function getpass(prompt::AbstractString)
-    print(prompt, ": ")
-    flush(stdout)
+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
@@ -478,12 +479,17 @@ function getpass(prompt::AbstractString)
     return s
 end
 else
-function getpass(prompt::AbstractString)
+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.
+getpass(prompt::AbstractString) = getpass(stdin, stdout, prompt)
+
 """
     prompt(message; default="") -> Union{String, Nothing}
 
@@ -493,15 +499,18 @@ then the user can enter just a newline character to select the `default`.
 
 See also `Base.getpass` and `Base.winprompt` for secure entry of passwords.
 """
-function prompt(message::AbstractString; default::AbstractString="")
+function prompt(input::IO, output::IO, message::AbstractString; default::AbstractString="")
     msg = !isempty(default) ? "$message [$default]: " : "$message: "
-    print(msg)
-    uinput = readline(keep=true)
+    print(output, msg)
+    uinput = readline(input, keep=true)
     isempty(uinput) && return nothing  # Encountered an EOF
     uinput = chomp(uinput)
     isempty(uinput) ? default : uinput
 end
 
+# allow new prompt methods to be defined if stdin has been
+# redirected to some custom stream, e.g. in IJulia.
+prompt(message::AbstractString; default::AbstractString="") = prompt(stdin, stdout, message, default=default)
 
 # Windows authentication prompt
 if Sys.iswindows()

test/misc.jl

@@ -408,6 +408,16 @@ let a = [1,2,3]
     @test a == [0,0,0]
 end
 
+# PR #28038 (prompt/getpass stream args)
+@test_throws MethodError Base.getpass(IOBuffer(), stdout, "pass")
+let buf = IOBuffer()
+    @test Base.prompt(IOBuffer("foo\nbar\n"), buf, "baz") == "foo"
+    @test String(take!(buf)) == "baz: "
+    @test Base.prompt(IOBuffer("\n"), buf, "baz", default="foobar") == "foobar"
+    @test String(take!(buf)) == "baz [foobar]: "
+    @test Base.prompt(IOBuffer("blah\n"), buf, "baz", default="foobar") == "blah"
+end
+
 # Test that we can VirtualProtect jitted code to writable
 @noinline function WeVirtualProtectThisToRWX(x, y)
     return x + y