From 2e84d74b095c7cf0c493a250d765993309558bb8 Mon Sep 17 00:00:00 2001
From: Daniel Pfister <80419299+0x2a-42@users.noreply.github.com>
Date: Tue, 31 Dec 2024 14:59:48 +0100
Subject: [PATCH] Add warning for empty rule

---
 src/frontend/diag.rs |  9 +++++++++
 src/frontend/sema.rs |  7 +++++--
 tests/frontend.rs    | 13 +++++++++++++
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/frontend/diag.rs b/src/frontend/diag.rs
index bc821f0..0bb46a0 100644
--- a/src/frontend/diag.rs
+++ b/src/frontend/diag.rs
@@ -34,6 +34,7 @@ pub const UNUSED_RULE: &str = "W001";
 pub const UNUSED_TOKEN: &str = "W002";
 pub const UNUSED_OPEN_NODE: &str = "W003";
 pub const REDUNDANT_ELISION: &str = "W004";
+pub const EMPTY_RULE: &str = "W005";
 
 pub trait LanguageErrors {
     fn invalid_binding_pos(span: &Span) -> Self;
@@ -67,6 +68,7 @@ pub trait LanguageErrors {
     fn redundant_elision(span: &Span) -> Self;
     fn expected_rule(span: &Span) -> Self;
     fn missing_node_name(span: &Span) -> Self;
+    fn empty_rule(span: &Span) -> Self;
 }
 
 impl LanguageErrors for Diagnostic {
@@ -359,4 +361,11 @@ impl LanguageErrors for Diagnostic {
             .with_message("missing node name")
             .with_labels(vec![Label::primary((), span.clone())])
     }
+
+    fn empty_rule(span: &Span) -> Self {
+        Diagnostic::warning()
+            .with_code(EMPTY_RULE)
+            .with_message("empty rule")
+            .with_labels(vec![Label::primary((), span.clone())])
+    }
 }
diff --git a/src/frontend/sema.rs b/src/frontend/sema.rs
index 0c9b4c0..bbd6981 100644
--- a/src/frontend/sema.rs
+++ b/src/frontend/sema.rs
@@ -258,8 +258,11 @@ impl<'a> GeneralCheck<'a> {
         diags: &mut Vec<Diagnostic>,
         sema: &mut SemanticData<'a>,
     ) {
-        rule.regex(cst)
-            .map(|regex| self.check_regex(cst, rule, regex, diags, sema, false, false));
+        if let Some(regex) = rule.regex(cst) {
+            self.check_regex(cst, rule, regex, diags, sema, false, false);
+        } else {
+            diags.push(Diagnostic::empty_rule(&rule.span(cst)));
+        }
         self.check_recursive(cst, sema, rule, diags);
         if let Some(regex) = rule.regex(cst) {
             let mut open = HashSet::new();
diff --git a/tests/frontend.rs b/tests/frontend.rs
index 1ce5c1a..2c359f4 100644
--- a/tests/frontend.rs
+++ b/tests/frontend.rs
@@ -167,6 +167,7 @@ fn lowercase_token() {
 
     assert_eq!(lines.next().unwrap(), "tests/frontend/lowercase_token.llw:1:7: error[E007]: token name starts with lower case letter");
     assert_eq!(lines.next().unwrap(), "tests/frontend/lowercase_token.llw:1:9: error[E007]: token name starts with lower case letter");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/lowercase_token.llw:4:1: warning[W005]: empty rule");
     assert_eq!(lines.next(), None);
 }
 
@@ -239,6 +240,10 @@ fn redefinition() {
     assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:14:1: error[E005]: redefinition of rule");
     assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:1:9: error[E005]: redefinition of token");
     assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:1:13: error[E005]: redefinition of token");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:6:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:9:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:12:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/redefinition.llw:14:1: warning[W005]: empty rule");
     assert_eq!(lines.next().unwrap(), "error[E008]: missing start rule");
     assert_eq!(lines.next(), None);
 }
@@ -309,6 +314,9 @@ fn unused_element() {
     let diags = gen_diags("tests/frontend/unused_element.llw");
     let mut lines = diags.lines();
 
+    assert_eq!(lines.next().unwrap(), "tests/frontend/unused_element.llw:13:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/unused_element.llw:20:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/unused_element.llw:23:1: warning[W005]: empty rule");
     assert_eq!(lines.next().unwrap(), "tests/frontend/unused_element.llw:9:1: warning[W001]: unused rule");
     assert_eq!(lines.next().unwrap(), "tests/frontend/unused_element.llw:13:1: warning[W001]: unused rule");
     assert_eq!(lines.next().unwrap(), "tests/frontend/unused_element.llw:23:1: warning[W001]: unused rule");
@@ -335,5 +343,10 @@ fn uppercase_rule() {
 
     assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:6:1: error[E006]: rule name starts with upper case letter");
     assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:9:1: error[E006]: rule name starts with upper case letter");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:3:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:6:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:9:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:12:1: warning[W005]: empty rule");
+    assert_eq!(lines.next().unwrap(), "tests/frontend/uppercase_rule.llw:15:1: warning[W005]: empty rule");
     assert_eq!(lines.next(), None);
 }