From 499aba9ca6eb3febfb16261b507145a39598c0b4 Mon Sep 17 00:00:00 2001
From: Justus Klausecker <justus@klausecker.de>
Date: Thu, 12 Mar 2026 11:47:45 +0100
Subject: [PATCH] Sema: require else prong for `comptime_int`

This fixes a bug introduced a couple of commits ago.
---
 src/Sema.zig                                  |   5 +-
 .../switch_validate_else_prong.zig            | 166 ++++++++++++++++++
 2 files changed, 168 insertions(+), 3 deletions(-)
 create mode 100644 test/cases/compile_errors/switch_validate_else_prong.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index 78f80b31e2..a6507865b7 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -11665,10 +11665,9 @@ fn validateSwitchBlock(
                 },
             };
         },
-        .int, .comptime_int, .@"union", .@"struct" => |type_tag| {
+        .int, .@"union", .@"struct" => |type_tag| {
             check_range: {
                 const int_ty = switch (type_tag) {
-                    .comptime_int => break :check_range, // comptime_int has 'infinite' range
                     .int => item_ty,
                     .@"union", .@"struct" => item_ty.bitpackBackingInt(zcu),
                     else => unreachable,
@@ -11696,7 +11695,7 @@ fn validateSwitchBlock(
                 }
             }
         },
-        .enum_literal, .@"fn", .pointer, .type => {
+        .comptime_int, .enum_literal, .@"fn", .pointer, .type => {
             if (!has_else) {
                 return sema.fail(
                     block,
diff --git a/test/cases/compile_errors/switch_validate_else_prong.zig b/test/cases/compile_errors/switch_validate_else_prong.zig
new file mode 100644
index 0000000000..4a1b3887b9
--- /dev/null
+++ b/test/cases/compile_errors/switch_validate_else_prong.zig
@@ -0,0 +1,166 @@
+const E = enum { a, b };
+export fn entry1() void {
+    switch (E.a) {
+        .a => {},
+    }
+}
+export fn entry2() void {
+    switch (E.a) {
+        .a, .b => {},
+        else => {},
+    }
+}
+
+const T = union(E) { a: u32, b };
+export fn entry3() void {
+    switch (T{ .a = 0 }) {
+        .a => {},
+    }
+}
+export fn entry4() void {
+    switch (T{ .a = 0 }) {
+        .a, .b => {},
+        else => {},
+    }
+}
+
+const Error = error{ MyError, MyOtherError };
+export fn entry5() void {
+    switch (Error.MyError) {
+        error.MyError => {},
+    }
+}
+export fn entry6() void {
+    switch (Error.MyError) {
+        error.MyError, error.MyOtherError => {},
+        else => {},
+    }
+}
+
+const U = packed union { a: u1, b: i1 };
+export fn entry7() void {
+    switch (U{ .a = 0 }) {
+        .{ .a = 0 } => {},
+    }
+}
+export fn entry8() void {
+    switch (U{ .a = 0 }) {
+        .{ .a = 0 }, .{ .a = 1 } => {},
+        else => {},
+    }
+}
+
+const S = packed struct { a: u1 };
+export fn entry9() void {
+    switch (S{ .a = 0 }) {
+        .{ .a = 0 } => {},
+    }
+}
+export fn entry10() void {
+    switch (S{ .a = 0 }) {
+        .{ .a = 0 }, .{ .a = 1 } => {},
+        else => {},
+    }
+}
+
+export fn entry11() void {
+    switch (@as(u1, 0)) {
+        0 => {},
+    }
+}
+export fn entry12() void {
+    switch (@as(u1, 0)) {
+        0, 1 => {},
+        else => {},
+    }
+}
+
+export fn entry13() void {
+    switch (true) {
+        true => {},
+    }
+}
+export fn entry14() void {
+    switch (true) {
+        true, false => {},
+        else => {},
+    }
+}
+
+export fn entry15() void {
+    switch ({}) {}
+}
+export fn entry16() void {
+    switch ({}) {
+        {} => {},
+        else => {},
+    }
+}
+
+export fn entry17() void {
+    switch (123) {
+        123 => {},
+    }
+}
+
+export fn entry18() void {
+    switch (.foo) {
+        .foo => {},
+    }
+}
+
+fn bar() void {}
+export fn entry19() void {
+    switch (bar) {
+        bar => {},
+    }
+}
+
+const baz: *u8 = @ptrFromInt(123);
+export fn entry20() void {
+    switch (baz) {
+        baz => {},
+    }
+}
+
+export fn entry21() void {
+    switch (u32) {
+        u32 => {},
+    }
+}
+
+export fn entry22() void {
+    switch (@as(anyerror, error.MyError)) {
+        error.MyError => {},
+    }
+}
+
+// error
+//
+// :3:5: error: switch must handle all possibilities
+// :1:21: note: unhandled enumeration value: 'b'
+// :1:11: note: enum 'tmp.E' declared here
+// :10:14: error: unreachable else prong; all cases already handled
+// :16:5: error: switch must handle all possibilities
+// :1:21: note: unhandled enumeration value: 'b'
+// :1:11: note: enum 'tmp.E' declared here
+// :23:14: error: unreachable else prong; all cases already handled
+// :29:5: error: switch must handle all possibilities
+// :29:5: note: unhandled error value: 'error.MyOtherError'
+// :36:14: error: unreachable else prong; all cases already handled
+// :42:5: error: switch must handle all possibilities
+// :49:14: error: unreachable else prong; all cases already handled
+// :55:5: error: switch must handle all possibilities
+// :62:14: error: unreachable else prong; all cases already handled
+// :67:5: error: switch must handle all possibilities
+// :74:14: error: unreachable else prong; all cases already handled
+// :79:5: error: switch must handle all possibilities
+// :86:14: error: unreachable else prong; all cases already handled
+// :91:5: error: switch must handle all possibilities
+// :96:14: error: unreachable else prong; all cases already handled
+// :101:5: error: else prong required when switching on type 'comptime_int'
+// :107:5: error: else prong required when switching on type '@EnumLiteral()'
+// :114:5: error: else prong required when switching on type 'fn () void'
+// :121:5: error: else prong required when switching on type '*u8'
+// :127:5: error: else prong required when switching on type 'type'
+// :133:5: error: else prong required when switching on type 'anyerror'