sema: print @Panic message at comptime

Author: xdBronch

src/Sema.zig

@@ -2024,7 +2024,7 @@ fn resolveConstString(
     block: *Block,
     src: LazySrcLoc,
     zir_ref: Zir.Inst.Ref,
-    reason: ComptimeReason,
+    reason: ?ComptimeReason,
 ) ![]u8 {
     const air_inst = try sema.resolveInst(zir_ref);
     return sema.toConstString(block, src, air_inst, reason);
@@ -2035,7 +2035,7 @@ pub fn toConstString(
     block: *Block,
     src: LazySrcLoc,
     air_inst: Air.Inst.Ref,
-    reason: ComptimeReason,
+    reason: ?ComptimeReason,
 ) ![]u8 {
     const pt = sema.pt;
     const coerced_inst = try sema.coerce(block, .slice_const_u8, air_inst, src);
@@ -5569,10 +5569,12 @@ fn zirPanic(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!void
     const src = block.nodeOffset(inst_data.src_node);
     const msg_inst = try sema.resolveInst(inst_data.operand);
 
-    const coerced_msg = try sema.coerce(block, .slice_const_u8, msg_inst, block.builtinCallArgSrc(inst_data.src_node, 0));
+    const arg_src = block.builtinCallArgSrc(inst_data.src_node, 0);
+    const coerced_msg = try sema.coerce(block, .slice_const_u8, msg_inst, arg_src);
 
     if (block.isComptime()) {
-        return sema.fail(block, src, "encountered @panic at comptime", .{});
+        const string = try sema.resolveConstString(block, arg_src, inst_data.operand, null);
+        return sema.fail(block, src, "encountered @panic at comptime: {s}", .{string});
     }
 
     // We only apply the first hint in a branch.
@@ -37261,7 +37263,7 @@ fn derefSliceAsArray(
     block: *Block,
     src: LazySrcLoc,
     slice_val: Value,
-    reason: ComptimeReason,
+    reason: ?ComptimeReason,
 ) CompileError!Value {
     return try sema.maybeDerefSliceAsArray(block, src, slice_val) orelse {
         return sema.failWithNeededComptime(block, src, reason);

test/cases/compile_errors/panic_called_at_compile_time.zig

@@ -8,4 +8,4 @@ export fn entry() void {
 
 // error
 //
-// :3:9: error: encountered @panic at comptime
+// :3:9: error: encountered @panic at comptime: aoeu