From c2d313dece1af23a2e492bdf3c5a1bd4eefb7c0e Mon Sep 17 00:00:00 2001
From: Richard Feldman <oss@rtfeldman.com>
Date: Sat, 6 Dec 2025 11:46:51 -0500
Subject: [PATCH] Improve comptime evaluator

---
 src/eval/comptime_evaluator.zig      |  8 +++-
 src/eval/test/comptime_eval_test.zig | 63 ++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/src/eval/comptime_evaluator.zig b/src/eval/comptime_evaluator.zig
index 1c29f677ed..10686f1470 100644
--- a/src/eval/comptime_evaluator.zig
+++ b/src/eval/comptime_evaluator.zig
@@ -1514,8 +1514,12 @@ pub const ComptimeEvaluator = struct {
                         try self.reportProblem(expect_info.message, expect_info.region, .expect_failed);
                     },
                     .error_eval => |error_info| {
-                        const error_name = @errorName(error_info.err);
-                        try self.reportProblem(error_name, error_info.region, .error_eval);
+                        // Provide user-friendly messages for specific errors
+                        const error_message = switch (error_info.err) {
+                            error.DivisionByZero => "Division by zero",
+                            else => @errorName(error_info.err),
+                        };
+                        try self.reportProblem(error_message, error_info.region, .error_eval);
                     },
                 }
             }
diff --git a/src/eval/test/comptime_eval_test.zig b/src/eval/test/comptime_eval_test.zig
index e174a78e6e..982fece6cd 100644
--- a/src/eval/test/comptime_eval_test.zig
+++ b/src/eval/test/comptime_eval_test.zig
@@ -1763,3 +1763,66 @@ test "comptime eval - to_str on unbound number literal" {
     // Flex var defaults to Dec; Dec.to_str is provided by builtins
     try testing.expectEqual(@as(usize, 0), result.problems.len());
 }
+
+// --- Division by zero tests ---
+
+test "comptime eval - division by zero produces error" {
+    const src =
+        \\x = 5 // 0
+    ;
+
+    var result = try parseCheckAndEvalModule(src);
+    defer cleanupEvalModule(&result);
+
+    const summary = try result.evaluator.evalAll();
+
+    // Should evaluate 1 declaration with no crashes (it's an error, not a crash)
+    try testing.expectEqual(@as(u32, 1), summary.evaluated);
+    try testing.expectEqual(@as(u32, 0), summary.crashed);
+
+    // Should have 1 problem reported (division by zero)
+    try testing.expect(result.problems.len() >= 1);
+    try testing.expect(errorContains(result.problems, "Division by zero"));
+}
+
+test "comptime eval - division by zero in expression" {
+    const src =
+        \\a = 10
+        \\b = 0
+        \\c = a // b
+    ;
+
+    var result = try parseCheckAndEvalModule(src);
+    defer cleanupEvalModule(&result);
+
+    const summary = try result.evaluator.evalAll();
+
+    // Should evaluate 3 declarations, c will cause an error
+    try testing.expectEqual(@as(u32, 3), summary.evaluated);
+
+    // Should have 1 problem reported (division by zero)
+    try testing.expect(result.problems.len() >= 1);
+    try testing.expect(errorContains(result.problems, "Division by zero"));
+}
+
+test "comptime eval - modulo by zero produces error" {
+    const src =
+        \\x = 10 % 0
+    ;
+
+    var result = try parseCheckAndEvalModule(src);
+    defer cleanupEvalModule(&result);
+
+    const summary = try result.evaluator.evalAll();
+
+    // Should evaluate 1 declaration
+    try testing.expectEqual(@as(u32, 1), summary.evaluated);
+
+    // Should have 1 problem reported (division by zero for modulo)
+    try testing.expect(result.problems.len() >= 1);
+    try testing.expect(errorContains(result.problems, "Division by zero"));
+}
+
+// Note: "division by zero does not halt other defs" test is skipped because
+// the interpreter state after an eval error may not allow continuing evaluation
+// of subsequent definitions that share the same evaluation context.