feat(experimental): Add invalid pattern syntax error (#7487)

compiler/noirc_frontend/src/elaborator/enums.rs

@@ -311,6 +311,14 @@ impl Elaborator<'_> {
             });
         };
 
+        // We want the actual expression's span here, not the innermost one from `type_location()`
+        let span = expression.location.span;
+        let syntax_error = |this: &mut Self| {
+            let errors = ResolverError::InvalidSyntaxInPattern { span };
+            this.push_err(errors, this.file);
+            Pattern::Error
+        };
+
         match expression.kind {
             ExpressionKind::Literal(Literal::Integer(value, negative)) => {
                 let actual = self.interner.next_type_variable_with_kind(Kind::IntegerOrField);
@@ -363,10 +371,7 @@ impl Elaborator<'_> {
                     }
                     Err(error) => {
                         self.push_err(error, location.file);
-                        // Default to defining a variable of the same name although this could
-                        // cause further match warnings/errors (e.g. redundant cases).
-                        let id = self.fresh_match_variable(expected_type.clone(), location);
-                        Pattern::Binding(id)
+                        Pattern::Error
                     }
                 }
             }
@@ -402,7 +407,7 @@ impl Elaborator<'_> {
                 if let StatementKind::Expression(expr) = self.interner.get_statement_kind(id) {
                     self.expression_to_pattern(expr.clone(), expected_type, variables_defined)
                 } else {
-                    panic!("Invalid expr kind {expression}")
+                    syntax_error(self)
                 }
             }
 
@@ -425,9 +430,7 @@ impl Elaborator<'_> {
             | ExpressionKind::AsTraitPath(_)
             | ExpressionKind::TypePath(_)
             | ExpressionKind::Resolved(_)
-            | ExpressionKind::Error => {
-                panic!("Invalid expr kind {expression}")
-            }
+            | ExpressionKind::Error => syntax_error(self),
         }
     }
 
@@ -703,6 +706,7 @@ impl Elaborator<'_> {
                 let (key, cons) = match col.pattern {
                     Pattern::Int(val) => ((val, val), Constructor::Int(val)),
                     Pattern::Range(start, stop) => ((start, stop), Constructor::Range(start, stop)),
+                    Pattern::Error => continue,
                     pattern => {
                         eprintln!("Unexpected pattern for integer type: {pattern:?}");
                         continue;
@@ -931,6 +935,11 @@ enum Pattern {
     /// 1 <= n < 20.
     #[allow(unused)]
     Range(SignedField, SignedField),
+
+    /// An error occurred while translating this pattern. This Pattern kind always translates
+    /// to a Fail branch in the decision tree, although the compiler is expected to halt
+    /// with errors before execution.
+    Error,
 }
 
 #[derive(Clone)]

compiler/noirc_frontend/src/hir/resolution/errors.rs

@@ -182,6 +182,8 @@ pub enum ResolverError {
     LoopNotYetSupported { span: Span },
     #[error("Expected a trait but found {found}")]
     ExpectedTrait { found: String, span: Span },
+    #[error("Invalid syntax in match pattern")]
+    InvalidSyntaxInPattern { span: Span },
     #[error("Variable '{existing}' was already defined in the same match pattern")]
     VariableAlreadyDefinedInPattern { existing: Ident, new_span: Span },
 }
@@ -694,6 +696,12 @@ impl<'a> From<&'a ResolverError> for Diagnostic {
                     String::new(),
                     *span)
             }
+            ResolverError::InvalidSyntaxInPattern { span } => {
+                Diagnostic::simple_error(
+                    "Invalid syntax in match pattern".into(), 
+                    "Only literal, constructor, and variable patterns are allowed".into(),
+                    *span)
+            },
             ResolverError::VariableAlreadyDefinedInPattern { existing, new_span } => {
                 let message = format!("Variable `{existing}` was already defined in the same match pattern");
                 let secondary = format!("`{existing}` redefined here");