test-locked-requirements: Improve logged output.

Run pip-compile with --quiet so we don’t have to redirect its stderr;
then we can see any exceptions it might throw.  Print any resulting
diff in the right order and without extra newlines separating each
line.

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

tools/test-locked-requirements

@@ -31,8 +31,7 @@ def print_diff(path_file1, path_file2):
                 fromfile=path_file1,
                 tofile=path_file2,
             )
-    for line in diff:
-        print(line)
+    sys.stdout.writelines(diff)
 
 def test_locked_requirements(tmp_dir):
     # type: (str) -> bool
@@ -44,8 +43,7 @@ def test_locked_requirements(tmp_dir):
         locked_file = os.path.join(REQS_DIR, fn)
         test_locked_file = os.path.join(tmp_dir, fn)
         shutil.copyfile(locked_file, test_locked_file)
-    subprocess.check_call([os.path.join(TOOLS_DIR, 'update-locked-requirements'), '--output-dir', tmp_dir],
-                          stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+    subprocess.check_call([os.path.join(TOOLS_DIR, 'update-locked-requirements'), '--output-dir', tmp_dir])
 
     same = True
     for fn in LOCKED_REQS_FILE_NAMES:
@@ -114,7 +112,7 @@ def main():
         for fn in LOCKED_REQS_FILE_NAMES:
             locked_file = os.path.join(REQS_DIR, fn)
             test_locked_file = os.path.join(tmp_dir, fn)
-            print_diff(test_locked_file, locked_file)
+            print_diff(locked_file, test_locked_file)
         # Flush the output to ensure we print the error at the end.
         sys.stdout.flush()
         raise Exception("It looks like you have updated some python dependencies but haven't "

tools/update-locked-requirements

@@ -12,7 +12,7 @@ compile_requirements () {
     output="$2"
     python_version="$3"
 
-    pip-compile --output-file "$output" "$source"
+    pip-compile --quiet --output-file "$output" "$source"
 
     # Remove the editable flag.  It's there because pip-compile can't
     # yet do without it (see