ttcn: add "template" ["(omit)" | "(value)" | "(present)"]

Modern TTCN3 has TemplateRestriction keywords, which improve detection
of invalid template use at compile time. They simply add one of
"(omit)", "(value)", "(present)" after the "template" keyword.

Example:

 template (value) ts_FOO_Request(integer bar := 0) :=
 	{ member := bar };

 template (present) tr_FOO_Request(template integer bar := *) :=
 	{ member := bar };

Before this patch, u-ctags would not tag these two definitons above,
making my work on the Osmocom test suite hard. (See
https://gitea.osmocom.org/ttcn3/osmo-ttcn3-hacks)

At first I tried to exactly match the three keywords within the braces,
but the token parsing does not support unrolling more than one token. So
if an unmatching token follows after the opening brace, I cannot un-get
the opening brace. The easiest solution, and one that also is tolerant
to keyword typos, is to just accept any braces after "template".

Related: ETSI ES 201 873-1 V4.14.1 § A.1.6.1.3

Units/parser-ttcn.r/ttcn-template-restriction.d/args.ctags

@@ -0,0 +1 @@
+--sort=no

Units/parser-ttcn.r/ttcn-template-restriction.d/expected.tags

@@ -0,0 +1,5 @@
+CoffeeTemplates	input.ttcn	/^module CoffeeTemplates$/;"	M
+AnyCoffee	input.ttcn	/^template (present) Coffee AnyCoffee$/;"	d
+SomeCoffee	input.ttcn	/^template (value) Coffee SomeCoffee(integer id, charstring description := "")$/;"	d
+Espresso	input.ttcn	/^template (omit) Coffee Espresso()$/;"	d
+Latte	input.ttcn	/^template (TYPO IN RESTRICTION) Coffee Latte()$/;"	d

Units/parser-ttcn.r/ttcn-template-restriction.d/input.ttcn

@@ -0,0 +1,32 @@
+import from CoffeeTypes all
+import from CoffeeConstants all
+
+module CoffeeTemplates
+{
+
+template (present) Coffee AnyCoffee
+{
+    id := ?,
+    description := ?
+}
+
+template (value) Coffee SomeCoffee(integer id, charstring description := "")
+{
+    id := id,
+   description := description
+}
+
+template (omit) Coffee Espresso()
+{
+    id := c_espressoId,
+    description := c_espresso
+}
+
+template (TYPO IN RESTRICTION) Coffee Latte()
+{
+    id := c_latteId,
+    description := c_latte
+}
+
+}
+

parsers/ttcn.c

@@ -625,6 +625,21 @@ static int matchExprOperator (void)
 	return 0;
 }
 
+/* Check if next token is one of "(omit)", "(value)", "(present)".
+ * ETSI ES 201 873-1 V4.14.1
+ * A.1.6.7 471. TemplateRestriction ::= "(" (OmitKeyword | ValueKeyword | PresentKeyword) ")"
+ * A.1.6.6 461. OmitKeyword ::= "omit"
+ * A.1.6.4.2 346. ValueKeyword ::= "value"
+ * A.1.6.1.3 145.PresentKeyword ::= "present"
+ */
+static int matchTemplateRestriction (void)
+{
+	/* Simplistic: do not verify the actual "omit"/"value"/"present" keyword, just skip the entire brackets when
+	 * present. This also is tolerant to typos in the keyword. Drawback: would also accept any amount of unrelated
+	 * tokens and punctuation in the braces. */
+	return matchBrackets(BR_PAR);
+}
+
 static int parseExprOperand (void)
 {
 	ttcnToken_t * pTok;
@@ -950,7 +965,8 @@ static void parseTTCN (void)
 				parseTypeDefBody();
 				break;
 			case T_TEMPLATE:
-				/* A.1.6.1.3 TemplateDef ::= "template" (Type | Signature) ID ... */
+				/* A.1.6.1.3 TemplateDef ::= "template" [TemplateRestriction] (Type | Signature) ID ... */
+				matchTemplateRestriction();
 				if (parseType() || parseSignature())
 					parseID(K_TEMPLATE);
 				break;