[osh/prompt] Implement \v and \V

Knock off test case #26 in spec/prompt, contributed by Simon Leary.

(Unrelated comments about HTM8)

data_lang/htm8-test.sh

@@ -5,6 +5,11 @@
 #
 # TODO:
 #
+# - htm8.py should use one-pass algorithm
+# - micro-syntax should check all errors
+#   - with tests
+#   - and then download CommonCrawl data set?
+#
 # - translate to C++
 #   - how to handle the regexes in the lexer?  Port to re2c directly?
 #   - for find(), do we need a C++ primitive for it?

osh/prompt.py

@@ -108,7 +108,14 @@ def __init__(self, lang, version_str, parse_ctx, mem):
 
         assert lang in ('osh', 'ysh'), lang
         self.lang = lang
-        self.version_str = version_str
+        self.version_str = version_str  # e.g. OSH version 0.26.0 is \V
+
+        # Calculate "0.26" for \v - shortened string that bash uses.  I guess
+        # this saves 2 chars in OSH too.
+        i = version_str.rfind('.')
+        assert i != -1, version_str
+        self.version_str_short = version_str[:i]
+
         self.parse_ctx = parse_ctx
         self.mem = mem
         # Cache to save syscalls / libc calls.
@@ -157,6 +164,9 @@ def PromptSubst(self, ch, arg=None):
             r = self.lang
 
         elif ch == 'v':
+            r = self.version_str_short
+
+        elif ch == 'V':
             r = self.version_str
 
         elif ch == 'A':

spec/prompt.test.sh

@@ -1,5 +1,5 @@
 ## compare_shells: bash
-## oils_failures_allowed: 9
+## oils_failures_allowed: 8
 
 #### sh -i
 # Notes: