Add first draft of new osproc.readLines (#15429)

* Add first draft of new osproc.readLines

* Add test for new osproc.readLines

* Rename test to start w/t to run; Also add newline to output

* Suppress hint messages.

* Output should match this time.

* Shoulda picked a program with simpler syntax than ..lol

* Address https://github.com/nim-lang/Nim/pull/15429#issuecomment-701890898
and https://github.com/nim-lang/Nim/pull/15429#issuecomment-701985976 by
factoring `readLines` into `iterator lines` and a wrapper `proc`.

* Address https://github.com/nim-lang/Nim/pull/15429#issuecomment-702127289
and also add a `ReadIOEffect` tag to the iterator (called by the wrapper..
so it should need no separate tag, if I understand correctly).

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/osproc/treadlines.nim b/tests/osproc/treadlines.nim
new file mode 100644
index 000000000..3a8303321
--- /dev/null
+++ b/tests/osproc/treadlines.nim
@@ -0,0 +1,20 @@
+discard """
+  output: '''Error: cannot open 'a.nim'
+Error: cannot open 'b.nim'
+'''
+  targets: "c"
+"""
+
+import osproc
+
+var ps: seq[Process] # compile & run 2 progs in parallel
+for prog in ["a", "b"]:
+  ps.add startProcess("nim", "",
+                      ["r", "--hint[Conf]=off", "--hint[Processing]=off", prog],
+                      options = {poUsePath, poDaemon, poStdErrToStdOut})
+
+for p in ps:
+  let (lines, exCode) = p.readLines
+  if exCode != 0:
+    for line in lines: echo line
+  p.close