tools: Add @must_use support to intrinsics.def

Emits the new OverloadFlag::kMustUse flag on the annotated overloads.
Nothing consumes this, yet.

Bug: tint:1844
Change-Id: I4eb0943a23eaf5de98cd63444a686cffe62fb36e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/120920
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

tools/src/tint/intrinsic/gen/gen.go

@@ -106,6 +106,8 @@ type Overload struct {
 	ReturnMatcherIndicesOffset *int
 	// StageUses describes the stages an overload can be used in
 	CanBeUsedInStage sem.StageUses
+	// True if the overload is marked as @must_use
+	MustUse bool
 	// True if the overload is marked as deprecated
 	IsDeprecated bool
 	// The kind of overload
@@ -211,6 +213,7 @@ func (b *IntrinsicTableBuilder) buildOverload(o *sem.Overload) (Overload, error)
 		ParametersOffset:           b.lut.parameters.Add(ob.parameters),
 		ReturnMatcherIndicesOffset: ob.returnTypeMatcherIndicesOffset,
 		CanBeUsedInStage:           o.CanBeUsedInStage,
+		MustUse:                    o.MustUse,
 		IsDeprecated:               o.IsDeprecated,
 		Kind:                       string(o.Decl.Kind),
 		ConstEvalFunction:          o.ConstEvalFunction,

tools/src/tint/intrinsic/resolver/resolve.go

@@ -345,6 +345,15 @@ func (r *resolver) intrinsic(
 			Compute:  true,
 		}
 	}
+	if mustUse := a.Attributes.Take("must_use"); mustUse != nil {
+		if len(mustUse.Values) > 0 {
+			return fmt.Errorf("%v @must_use does not accept any arguments", mustUse.Source)
+		}
+		if a.ReturnType == nil {
+			return fmt.Errorf("%v @must_use can only be used on a function with a return type", mustUse.Source)
+		}
+		overload.MustUse = true
+	}
 	if constEvalFn := a.Attributes.Take("const"); constEvalFn != nil {
 		switch len(constEvalFn.Values) {
 		case 0:

tools/src/tint/intrinsic/resolver/resolver_test.go

@@ -177,6 +177,11 @@ type f32
 type T<x>
 conv f32(T<f32>)`,
 			success,
+		}, {
+			`
+type f32
+@must_use fn f() -> f32`,
+			success,
 		}, {
 			`enum E {A A}`,
 			`
@@ -518,6 +523,10 @@ type P<T>
 match m: f32
 fn f(P<m>)`,
 			`file.txt:4:8 type matcher cannot be used directly here. Use a matcher constrained template argument`,
+		}, {
+			`
+@must_use fn f()`,
+			`file.txt:1:2 @must_use can only be used on a function with a return type`,
 		},
 	} {
 

tools/src/tint/intrinsic/sem/sem.go

@@ -182,6 +182,7 @@ type Overload struct {
 	ReturnType        *FullyQualifiedName
 	Parameters        []Parameter
 	CanBeUsedInStage  StageUses
+	MustUse           bool   // True if function cannot be used as a statement
 	IsDeprecated      bool   // True if this overload is deprecated
 	ConstEvalFunction string // Name of the function used to evaluate the intrinsic at shader creation time
 }