lib/parse-sexp: add '*' as syntactic sugar for '(starts-with "")'

Users that insist on using a literal '*' as a tag, can continue to do
so by quoting it when searching.

doc/man7/notmuch-sexp-queries.rst

@@ -36,8 +36,11 @@ An s-expression query is either an atom, the empty list, or a
 a *field*, *logical operation*, or *modifier*, and 0 or more
 subqueries.
 
-``*`` ``()``
+``*``
-    Match all messages.
+   "*" matches any non-empty string in the current field.
+
+``()``
+    The empty list matches all messages
 
 *term*
 
@@ -138,6 +141,15 @@ from terms, operators, and modifiers, but not other fields.
 MODIFIERS
 `````````
 
+*Modifiers* refer to any prefixes (first elements of compound queries)
+that are neither operators nor fields.
+
+``(starts-with`` *subword* ``)``
+    Matches any term starting with *subword*.  This applies in either
+    phrase or term :any:`fields <fields>`, or outside of fields [#not-body]_. Note that
+    a ``starts-with`` query cannot be part of a phrase. The
+    atom ``*`` is a synonym for ``(starts-with "")``.
+
 EXAMPLES
 ========
 
@@ -181,6 +193,9 @@ EXAMPLES
     "mallory@example.org", and also "bob@example.com.au" since it
     contains the adjacent triple "bob", "example", "com".
 
+``(not (to *))``
+    Match messages with an empty or invalid 'To' and 'Cc' field.
+
 NOTES
 =====
 

lib/parse-sexp.cc

@@ -176,6 +176,11 @@ _sexp_to_xapian_query (notmuch_database_t *notmuch, const _sexp_prefix_t *parent
 	std::string term = Xapian::Unicode::tolower (sx->val);
 	Xapian::Stem stem = *(notmuch->stemmer);
 	std::string term_prefix = parent ? _find_prefix (parent->name) : "";
+
+	if (sx->aty == SEXP_BASIC && strcmp (sx->val, "*") == 0) {
+	    return _sexp_parse_wildcard (notmuch, parent, "", output);
+	}
+
 	if (parent && (parent->flags & SEXP_FLAG_BOOLEAN)) {
 	    output = Xapian::Query (term_prefix + sx->val);
 	    return NOTMUCH_STATUS_SUCCESS;

test/T081-sexpr-search.sh

@@ -386,6 +386,46 @@ thread:XXX   2000-01-01 [1/1] Notmuch Test Suite; search by to (name) (inbox unr
 EOF
 test_expect_equal_file EXPECTED OUTPUT
 
+test_begin_subtest "wildcard search for 'is'"
+notmuch search not id:${notag_mid} > EXPECTED
+notmuch search --query=sexp '(is *)' > OUTPUT
+test_expect_equal_file EXPECTED OUTPUT
+
+test_begin_subtest "negated wildcard search for 'is'"
+notmuch search id:${notag_mid} > EXPECTED
+notmuch search --query=sexp '(not (is *))' > OUTPUT
+test_expect_equal_file EXPECTED OUTPUT
+
+test_begin_subtest "wildcard search for 'property'"
+notmuch search property:foo=bar > EXPECTED
+notmuch search --query=sexp '(property *)' > OUTPUT
+test_expect_equal_file EXPECTED OUTPUT
+
+test_begin_subtest "wildcard search for 'tag'"
+notmuch search not id:${notag_mid} > EXPECTED
+notmuch search --query=sexp '(tag *)' > OUTPUT
+test_expect_equal_file EXPECTED OUTPUT
+
+test_begin_subtest "negated wildcard search for 'tag'"
+notmuch search id:${notag_mid} > EXPECTED
+notmuch search --query=sexp '(not (tag *))' > OUTPUT
+test_expect_equal_file EXPECTED OUTPUT
+
+add_message '[subject]="message with tag \"*\""'
+notmuch tag '+*' id:${gen_msg_id}
+
+test_begin_subtest "search for 'tag' \"*\""
+output=$(notmuch search --query=sexp --output=messages '(tag "*")')
+test_expect_equal "$output" "id:$gen_msg_id"
+
+test_begin_subtest "search for missing / empty to"
+add_message [to]="undisclosed-recipients:"
+notmuch search --query=sexp '(not (to *))' | notmuch_search_sanitize > OUTPUT
+cat <<EOF > EXPECTED
+thread:XXX   2001-01-05 [1/1] Notmuch Test Suite; search for missing / empty to (inbox unread)
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
 test_begin_subtest "Unbalanced parens"
 # A code 1 indicates the error was handled (a crash will return e.g. 139).
 test_expect_code 1 "notmuch search --query=sexp '('"
@@ -454,4 +494,12 @@ notmuch search: Syntax error in query
 EOF
 test_expect_equal_file EXPECTED OUTPUT
 
+test_begin_subtest "wildcard, illegal field"
+notmuch search --query=sexp '(body *)' >OUTPUT 2>&1
+cat <<EOF > EXPECTED
+notmuch search: Syntax error in query
+'body' does not support wildcard queries
+EOF
+test_expect_equal_file EXPECTED OUTPUT
+
 test_done