config: highlight parse error caused by leading spaces (issue3214)

Added "unexpected leading whitespace" message to parse error
when .hgrc has a line that starts with whitespace.
Helps new users unfamiliar with syntax of rc file.

mercurial/dispatch.py

@@ -58,6 +58,8 b' def dispatch(req):'
         if len(inst.args) > 1:
             ferr.write(_("hg: parse error at %s: %s\n") %
                              (inst.args[1], inst.args[0]))
+            if (inst.args[0][0] == ' '):
+                ferr.write(_("unexpected leading whitespace\n"))
         else:
             ferr.write(_("hg: parse error: %s\n") % inst.args[0])
         return -1
@@ -155,6 +157,8 b' def _runcatch(req):'
         if len(inst.args) > 1:
             ui.warn(_("hg: parse error at %s: %s\n") %
                              (inst.args[1], inst.args[0]))
+            if (inst.args[0][0] == ' '):
+                ui.warn(_("unexpected leading whitespace\n"))
         else:
             ui.warn(_("hg: parse error: %s\n") % inst.args[0])
         return -1

tests/test-config.t

@@ -19,6 +19,25 b' Invalid syntax: no key'
   hg: parse error at $TESTTMP/.hg/hgrc:1: =nokeyvalue
   [255]
 
+Test hint about invalid syntax from leading white space
+
+  $ cat > .hg/hgrc << EOF
+  >  key=value
+  > EOF
+  $ hg showconfig
+  hg: parse error at $TESTTMP/.hg/hgrc:1:  key=value
+  unexpected leading whitespace
+  [255]
+
+  $ cat > .hg/hgrc << EOF
+  >  [section]
+  > key=value
+  > EOF
+  $ hg showconfig
+  hg: parse error at $TESTTMP/.hg/hgrc:1:  [section]
+  unexpected leading whitespace
+  [255]
+
 Reset hgrc
 
   $ echo > .hg/hgrc

tests/test-hgrc.t

@@ -43,6 +43,7 b' issue1829: wrong indentation'
   $ echo '  x = y' >> $HGRC
   $ hg version
   hg: parse error at $TESTTMP/hgrc:2:   x = y
+  unexpected leading whitespace
   [255]
 
   $ python -c "print '[foo]\nbar = a\n b\n c \n  de\n fg \nbaz = bif cb \n'" \