Allow no Mercurial installed

.github/workflows/ci.yml

@@ -42,7 +42,7 @@ jobs:
         run: |
           python .github/debug_which_hg.py
       - if: runner.os != 'Windows'
-        name: Mercurial installation
+        name: Check Mercurial installation
         run: |
           hg version -v
           hg debuginstall

src/hg_setup/__init__.py

@@ -1,10 +1,7 @@
 """hg-setup package"""
 
-import os
 import sys
 
-from pathlib import Path
-
 import rich_click as click
 
 from .init_cmd import init_tui, init_auto

src/hg_setup/hgrcs.py

@@ -5,9 +5,10 @@
 
 from pathlib import Path
 
-from textwrap import dedent
 from shutil import which
 
+import rich_click as click
+
 
 name_default = ".hgrc" if os.name != "nt" else "mercurial.ini"
 
@@ -32,18 +33,27 @@ def check_hg_conf_file():
 class HgrcCodeMaker:
     def __init__(self):
         # get pythonexe to be able to check installation of
-        process = subprocess.run(
-            ["hg", "debuginstall", "-T", "{pythonexe}"],
-            capture_output=True,
-            # cannot use check=True
-            check=False,
-            text=True,
-        )
-        pythonexe = process.stdout
-        if not Path(pythonexe).exists():
-            raise ValueError(str(process))
+        try:
+            process = subprocess.run(
+                ["hg", "debuginstall", "-T", "{pythonexe}"],
+                capture_output=True,
+                # cannot use check=True
+                check=False,
+                text=True,
+            )
+        except FileNotFoundError:
+            click.secho("hg not found", fg="red")
+            hg_error = True
+        else:
+            hg_error = False
+            pythonexe = process.stdout
+            if not Path(pythonexe).exists():
+                raise ValueError(str(process))
+
+            if pythonexe.endswith("hg.exe"):
+                hg_error = True
 
-        if pythonexe.endswith("hg.exe"):
+        if hg_error:
             # this can happen on Windows!
             self.enable_hggit = self.enable_topic = True
         else: