add compile error for slice of undefined slice

closes #1293

2 files changed, 15 insertions, 0 deletions

diff --git a/src/ir.cpp b/src/ir.cpp
index a35c6380a7..7e98e99af1 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -19229,6 +19229,11 @@ static ZigType *ir_analyze_instruction_slice(IrAnalyze *ira, IrInstructionSlice
                 return ira->codegen->builtin_types.entry_invalid;
 
             parent_ptr = &slice_ptr->data.x_struct.fields[slice_ptr_index];
+            if (parent_ptr->special == ConstValSpecialUndef) {
+                ir_add_error(ira, &instruction->base, buf_sprintf("slice of undefined"));
+                return ira->codegen->builtin_types.entry_invalid;
+            }
+
             ConstExprValue *len_val = &slice_ptr->data.x_struct.fields[slice_len_index];
 
             switch (parent_ptr->data.x_ptr.special) {
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index c1e25c1df9..62df9f077d 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -2,6 +2,16 @@ const tests = @import("tests.zig");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
     cases.add(
+        "comptime slice of an undefined slice",
+        \\comptime {
+        \\    var a: []u8 = undefined;
+        \\    var b = a[0..10];
+        \\}
+    ,
+        ".tmp_source.zig:3:14: error: slice of undefined",
+    );
+
+    cases.add(
         "implicit cast const array to mutable slice",
         \\export fn entry() void {
         \\    const buffer: [1]u8 = []u8{8};