intrinsics: Add new struct form of modf(), frexp()

Implement these for all the writers.
SPIR-V reader not implemented (the old overloads weren't implemented either).

Deprecate the old overloads.

Fixed: tint:54
Change-Id: If66d26dbac3389ff604734f31b426abe47868b91
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/59302
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>

tools/src/cmd/intrinsic-gen/gen/generate.go

@@ -58,6 +58,8 @@ func (g *generator) generate(tmpl string, w io.Writer, writeFile WriteFile) erro
 		"SplitDisplayName":      splitDisplayName,
 		"HasPrefix":             strings.HasPrefix,
 		"HasSuffix":             strings.HasSuffix,
+		"TrimPrefix":            strings.TrimPrefix,
+		"TrimSuffix":            strings.TrimSuffix,
 		"IsEnumEntry":           is(sem.EnumEntry{}),
 		"IsEnumMatcher":         is(sem.EnumMatcher{}),
 		"IsFQN":                 is(sem.FullyQualifiedName{}),
@@ -66,6 +68,7 @@ func (g *generator) generate(tmpl string, w io.Writer, writeFile WriteFile) erro
 		"IsTemplateNumberParam": is(sem.TemplateNumberParam{}),
 		"IsTemplateTypeParam":   is(sem.TemplateTypeParam{}),
 		"IsType":                is(sem.Type{}),
+		"IsDeclarable":          isDeclarable,
 		"IsFirstIn":             isFirstIn,
 		"IsLastIn":              isLastIn,
 		"IntrinsicTable":        g.intrinsicTable,
@@ -200,6 +203,13 @@ func iterate(n int) []int {
 	return out
 }
 
+// isDeclarable returns false if the FullyQualifiedName starts with a
+// leading underscore. These are undeclarable as WGSL does not allow identifers
+// to have a leading underscore.
+func isDeclarable(fqn sem.FullyQualifiedName) bool {
+	return !strings.HasPrefix(fqn.Target.GetName(), "_")
+}
+
 // pascalCase returns the snake-case string s transformed into 'PascalCase',
 // Rules:
 // * The first letter of the string is capitalized

tools/src/cmd/intrinsic-gen/gen/permutate.go

@@ -364,6 +364,10 @@ func validate(fqn sem.FullyQualifiedName, uses *sem.StageUses) bool {
 		}
 	}
 
+	if !isDeclarable(fqn) {
+		return false
+	}
+
 	for _, arg := range fqn.TemplateArguments {
 		if argFQN, ok := arg.(sem.FullyQualifiedName); ok {
 			if !validate(argFQN, uses) {

tools/src/cmd/intrinsic-gen/lexer/lexer.go

@@ -91,7 +91,7 @@ func (l *lexer) lex() error {
 			case l.match("enum", tok.Enum):
 			case l.match("type", tok.Type):
 			case l.match("match", tok.Match):
-			case unicode.IsLetter(l.peek(0)):
+			case unicode.IsLetter(l.peek(0)) || l.peek(0) == '_':
 				l.tok(l.count(alphaNumericOrUnderscore), tok.Identifier)
 			case unicode.IsNumber(l.peek(0)):
 				l.tok(l.count(unicode.IsNumber), tok.Integer)

tools/src/cmd/intrinsic-gen/lexer/lexer_test.go

@@ -40,6 +40,9 @@ func TestLexTokens(t *testing.T) {
 		{"ident_123", tok.Token{Kind: tok.Identifier, Runes: []rune("ident_123"), Source: tok.Source{
 			S: loc(1, 1, 0), E: loc(1, 10, 9),
 		}}},
+		{"_ident_", tok.Token{Kind: tok.Identifier, Runes: []rune("_ident_"), Source: tok.Source{
+			S: loc(1, 1, 0), E: loc(1, 8, 7),
+		}}},
 		{"123456789", tok.Token{Kind: tok.Integer, Runes: []rune("123456789"), Source: tok.Source{
 			S: loc(1, 1, 0), E: loc(1, 10, 9),
 		}}},