add HGRCPATH env var, list of places to look for hgrc files.

if set, override default hgrc search path.
if empty, only .hg/hgrc of current repo read.

for each element, if directory, all entries in directory with end in
".rc" are added to path.  else, element is added to path.

big thing about this change is that user "~/.hgrc" and system hgrc not
longer breaks tests.  run-tests makes HGRCPATH empty now.

doc/hg.1.txt

@@ -146,6 +146,16 b' HGMERGE::'
 
     (deprecated, use .hgrc)
 
+HGRCPATH::
+    A list of files or directories to search for hgrc files.  Item
+    separator is ":" on Unix, ";" on Windows.  If HGRCPATH is not set,
+    platform default search path is used.  If empty, only .hg/hgrc of
+    current repository is read.
+
+    For each element in path, if a directory, all entries in directory
+    ending with ".rc" are added to path.  Else, element itself is
+    added to path.
+
 HGUSER::
     This is the string used for the author of a commit.
 

mercurial/ui.py

@@ -18,7 +18,7 b' class ui(object):'
             # this is the parent of all ui children
             self.parentui = None
             self.cdata = ConfigParser.SafeConfigParser()
-            self.readconfig(util.rcpath)
+            self.readconfig(util.rcpath())
 
             self.quiet = self.configbool("ui", "quiet")
             self.verbose = self.configbool("ui", "verbose")

mercurial/util.py

@@ -506,17 +506,18 b" if os.name == 'nt':"
 
     sys.stdout = winstdout(sys.stdout)
 
-    try:
-        import win32api, win32process
-        filename = win32process.GetModuleFileNameEx(win32api.GetCurrentProcess(), 0)
-        systemrc = os.path.join(os.path.dirname(filename), 'mercurial.ini')
+    def os_rcpath():
+        '''return default os-specific hgrc search path'''
+        try:
+            import win32api, win32process
+            proc = win32api.GetCurrentProcess()
+            filename = win32process.GetModuleFileNameEx(proc, 0)
+            systemrc = os.path.join(os.path.dirname(filename), 'mercurial.ini')
+        except ImportError:
+            systemrc = r'c:\mercurial\mercurial.ini'
 
-    except ImportError:
-        systemrc = r'c:\mercurial\mercurial.ini'
-        pass
-
-    rcpath = (systemrc,
-              os.path.join(os.path.expanduser('~'), 'mercurial.ini'))
+        return [systemrc,
+                os.path.join(os.path.expanduser('~'), 'mercurial.ini')]
 
     def parse_patch_output(output_line):
         """parses the output produced by patch and returns the file name"""
@@ -591,12 +592,17 b' else:'
                         if f.endswith(".rc")])
         except OSError, inst: pass
         return rcs
-    rcpath = []
-    if len(sys.argv) > 0:
-        rcpath.extend(rcfiles(os.path.dirname(sys.argv[0]) + '/../etc/mercurial'))
-    rcpath.extend(rcfiles('/etc/mercurial'))
-    rcpath.append(os.path.expanduser('~/.hgrc'))
-    rcpath = [os.path.normpath(f) for f in rcpath]
+
+    def os_rcpath():
+        '''return default os-specific hgrc search path'''
+        path = []
+        if len(sys.argv) > 0:
+            path.extend(rcfiles(os.path.dirname(sys.argv[0]) +
+                                  '/../etc/mercurial'))
+        path.extend(rcfiles('/etc/mercurial'))
+        path.append(os.path.expanduser('~/.hgrc'))
+        path = [os.path.normpath(f) for f in path]
+        return path
 
     def parse_patch_output(output_line):
         """parses the output produced by patch and returns the file name"""
@@ -768,3 +774,29 b' def walkrepos(path):'
                 yield root
                 dirs[:] = []
                 break
+
+_rcpath = None
+
+def rcpath():
+    '''return hgrc search path. if env var HGRCPATH is set, use it.
+    for each item in path, if directory, use files ending in .rc,
+    else use item.
+    make HGRCPATH empty to only look in .hg/hgrc of current repo.
+    if no HGRCPATH, use default os-specific path.'''
+    global _rcpath
+    if _rcpath is None:
+        if 'HGRCPATH' in os.environ:
+            _rcpath = []
+            for p in os.environ['HGRCPATH'].split(os.pathsep):
+                if not p: continue
+                try:
+                    for f in os.listdir(p):
+                        if f.endswith('.rc'):
+                            _rcpath.append(os.path.join(p, f))
+                    continue
+                except:
+                    pass
+                _rcpath.append(p)
+        else:
+            _rcpath = os_rcpath()
+    return _rcpath

tests/run-tests

@@ -18,6 +18,7 b' TZ=GMT; export TZ'
 HGEDITOR=true; export HGEDITOR
 HGMERGE=true; export HGMERGE
 HGUSER="test"; export HGUSER
+HGRCPATH=""; export HGRCPATH
 
 ECHO_N="echo -n"
 [ -x /usr/ucb/echo ] && ECHO_N="/usr/ucb/echo -n"