Add character literal parsing and validation

crates/ra_syntax/src/validation.rs

@@ -0,0 +1,40 @@
+use crate::{
+    ast::{self, AstNode},
+    File,
+    string_lexing,
+    yellow::{
+        SyntaxError,
+    },
+};
+
+pub(crate) fn validate(file: &File) -> Vec<SyntaxError> {
+    let mut errors = Vec::new();
+    for d in file.root.borrowed().descendants() {
+        if let Some(c) = ast::Char::cast(d) {
+            let components = &mut string_lexing::parse_char_literal(c.text());
+            let len = components.count();
+
+            if !components.has_closing_quote {
+                errors.push(SyntaxError {
+                    msg: "Unclosed char literal".to_string(),
+                    offset: d.range().start(),
+                });
+            }
+
+            if len == 0 {
+                errors.push(SyntaxError {
+                    msg: "Empty char literal".to_string(),
+                    offset: d.range().start(),
+                });
+            }
+
+            if len > 1 {
+                errors.push(SyntaxError {
+                    msg: "Character literal should be only one character long".to_string(),
+                    offset: d.range().start(),
+                });
+            }
+        }
+    }
+    errors
+}