From 3cd9c9a4346f10fd1c772b8ecd4258d6df2ff901 Mon Sep 17 00:00:00 2001
From: Tim Voronov <ziflex@gmail.com>
Date: Tue, 12 Aug 2025 13:18:49 -0400
Subject: [PATCH] Enhance diagnostics for incomplete ternary expressions:
 improve error messages and hints for missing expressions after '?' and ':' in
 ternary operator, and add comprehensive test cases for better clarity and
 coverage.

---
 .../diagnostics/match_common_errors.go        | 30 ++++++++++++++++
 .../compiler/compiler_errors_syntax_test.go   | 36 +++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/pkg/compiler/internal/diagnostics/match_common_errors.go b/pkg/compiler/internal/diagnostics/match_common_errors.go
index 41f519d8..00d764d0 100644
--- a/pkg/compiler/internal/diagnostics/match_common_errors.go
+++ b/pkg/compiler/internal/diagnostics/match_common_errors.go
@@ -39,6 +39,36 @@ func matchCommonErrors(src *file.Source, err *CompilationError, offending *Token
 			return true
 		}
 
+		// Ternary operator, incomplete expression
+		if is(offending.Prev(), "?") {
+			span := spanFromTokenSafe(offending.Prev().Token(), src)
+			span.Start++
+			span.End++
+
+			err.Message = "Expected expression after '?' in ternary operator"
+			err.Hint = "Provide an expression after the question mark to complete the ternary operation."
+			err.Spans = []ErrorSpan{
+				NewMainErrorSpan(span, "missing expression"),
+			}
+
+			return true
+		}
+
+		// Ternary operator, missing the right-hand expression
+		if is(offending.Prev(), ":") {
+			span := spanFromTokenSafe(offending.Prev().Token(), src)
+			span.Start++
+			span.End++
+
+			err.Message = "Expected expression after ':' in ternary operator"
+			err.Hint = "Provide an expression after the colon to complete the ternary operation."
+			err.Spans = []ErrorSpan{
+				NewMainErrorSpan(span, "missing expression"),
+			}
+
+			return true
+		}
+
 		input := extractNoAlternativeInputs(err.Message)
 		token := input[len(input)-1]
 
diff --git a/test/integration/compiler/compiler_errors_syntax_test.go b/test/integration/compiler/compiler_errors_syntax_test.go
index cb97d356..b490331f 100644
--- a/test/integration/compiler/compiler_errors_syntax_test.go
+++ b/test/integration/compiler/compiler_errors_syntax_test.go
@@ -302,6 +302,42 @@ func TestSyntaxErrors(t *testing.T) {
 				Hint:    "Provide an expression after the logical operator, e.g. (a AND b).",
 			}, "Incomplete logical expression 4"),
 
+		ErrorCase(
+			`
+			LET a = 1
+			LET b = 2
+			LET i = b > 1 ? a :
+			RETURN i
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected expression after ':' in ternary operator",
+				Hint:    "Provide an expression after the colon to complete the ternary operation.",
+			}, "Incomplete ternary expression"),
+
+		ErrorCase(
+			`
+			LET a = 1
+			LET b = 2
+			LET i = b > 1 ? 1 + 1 + 1 :
+			RETURN i
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected expression after ':' in ternary operator",
+				Hint:    "Provide an expression after the colon to complete the ternary operation.",
+			}, "Incomplete ternary expression 2"),
+
+		ErrorCase(
+			`
+			LET a = 1
+			LET b = 2
+			LET i = b > 1 ?
+			RETURN i
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected expression after '?' in ternary operator",
+				Hint:    "Provide an expression after the question mark to complete the ternary operation.",
+			}, "Incomplete ternary expression 3"),
+
 		SkipErrorCase(
 			`
 			LET i = NONE