[valid] Check that switches have a default case (#1529)

From the WGSL spec: "Each switch statement must have exactly one default clause."

src/valid/function.rs

@@ -106,6 +106,8 @@ pub enum FunctionError {
     InvalidSwitchType(Handle<crate::Expression>),
     #[error("Multiple `switch` cases for {0:?} are present")]
     ConflictingSwitchCase(i32),
+    #[error("The `switch` is missing a `default` case")]
+    MissingDefaultCase,
     #[error("Multiple `default` cases are present")]
     MultipleDefaultCases,
     #[error("The last `switch` case contains a `falltrough`")]
@@ -471,6 +473,10 @@ impl super::Validator {
                             }
                         }
                     }
+                    if !default {
+                        return Err(FunctionError::MissingDefaultCase
+                            .with_span_static(span, "missing default case"));
+                    }
                     if let Some(case) = cases.last() {
                         if case.fall_through {
                             return Err(FunctionError::LastCaseFallTrough.with_span_static(

tests/in/control-flow.wgsl

@@ -36,6 +36,8 @@ fn main([[builtin(global_invocation_id)]] global_id: vec3<u32>) {
 	switch(0u) {
 		case 0u: {
 		}
+        default: {
+        }
 	}
 
     // non-empty switch in last-statement-in-function position
@@ -71,6 +73,7 @@ fn switch_case_break() {
         case 0: {
             break;
         }
+        default: {}
     }
     return;
 }
@@ -81,6 +84,7 @@ fn loop_switch_continue(x: i32) {
             case 1: {
                 continue;
             }
+            default: {}
         }
     }
 }

tests/out/glsl/control-flow.main.Compute.glsl

@@ -17,6 +17,8 @@ void switch_case_break() {
     switch(0) {
         case 0:
             break;
+        default:
+            break;
     }
     return;
 }
@@ -26,6 +28,8 @@ void loop_switch_continue(int x) {
         switch(x) {
             case 1:
                 continue;
+            default:
+                break;
         }
     }
     return;
@@ -61,6 +65,8 @@ void main() {
     switch(0u) {
         case 0u:
             break;
+        default:
+            break;
     }
     int _e10 = pos;
     switch(_e10) {

tests/out/hlsl/control-flow.hlsl

@@ -14,6 +14,9 @@ void switch_case_break()
         case 0: {
             break;
         }
+        default: {
+            break;
+        }
     }
     return;
 }
@@ -25,6 +28,9 @@ void loop_switch_continue(int x)
             case 1: {
                 continue;
             }
+            default: {
+                break;
+            }
         }
     }
     return;
@@ -71,6 +77,9 @@ void main(uint3 global_id : SV_DispatchThreadID)
         case 0u: {
             break;
         }
+        default: {
+            break;
+        }
     }
     int _expr10 = pos;
     switch(_expr10) {

tests/out/msl/control-flow.msl

@@ -19,6 +19,9 @@ void switch_case_break(
         case 0: {
             break;
         }
+        default: {
+            break;
+        }
     }
     return;
 }
@@ -31,6 +34,9 @@ void loop_switch_continue(
             case 1: {
                 continue;
             }
+            default: {
+                break;
+            }
         }
     }
     return;
@@ -75,6 +81,9 @@ kernel void main_(
         case 0u: {
             break;
         }
+        default: {
+            break;
+        }
     }
     int _e10 = pos;
     switch(_e10) {

tests/out/wgsl/control-flow.wgsl

@@ -11,6 +11,8 @@ fn switch_case_break() {
         case 0: {
             break;
         }
+        default: {
+        }
     }
     return;
 }
@@ -21,6 +23,8 @@ fn loop_switch_continue(x: i32) {
             case 1: {
                 continue;
             }
+            default: {
+            }
         }
     }
     return;
@@ -59,6 +63,8 @@ fn main([[builtin(global_invocation_id)]] global_id: vec3<u32>) {
     switch(0u) {
         case 0u: {
         }
+        default: {
+        }
     }
     let e10: i32 = pos;
     switch(e10) {

tests/wgsl-errors.rs

@@ -995,6 +995,7 @@ fn last_case_falltrough() {
         "
         fn test_falltrough() {
           switch(0) {
+            default: {}
             case 0: {
               fallthrough;
             }
@@ -1009,3 +1010,22 @@ fn last_case_falltrough() {
         )
     }
 }
+
+#[test]
+fn missing_default_case() {
+    check_validation_error! {
+        "
+        fn test_missing_default_case() {
+          switch(0) {
+            case 0: {}
+          }
+        }
+        ":
+        Err(
+            naga::valid::ValidationError::Function {
+                error: naga::valid::FunctionError::MissingDefaultCase,
+                ..
+            },
+        )
+    }
+}