test(asm): pin the flag-list TEXT shapes against the toolchain

Assisted-by: GLM 5.3 Flash

parser/flags.go

@@ -77,7 +77,8 @@ func flagsRun(g []token.Token) []token.Token {
 // evalFlags evaluates one flags operand.  Every identifier must name a
 // flag in textFlags; the toolchain rejects any other with "unexpected NAME
 // evaluating expression", and so does this.  The whole operand folds to
-// one integer, which is returned as the value.
+// one integer, which is returned as the value.  pseudo names the directive
+// in the toolchain's own diagnostics ("TEXT", "GLOBL").
 //
 // The names returned follow the operand's own spelling: an operand written
 // purely as names keeps them in written order, duplicates included, the
@@ -89,17 +90,21 @@ func flagsRun(g []token.Token) []token.Token {
 // After a failure the names collected so far are returned with value 0:
 // the tree stays usable beside the diagnostic, and value 0 is exactly the
 // flags the assembler can trust the operand for.
-func (p *state) evalFlags(g []token.Token, keepWritten bool) ([]string, int64) {
+func (p *state) evalFlags(g []token.Token, keepWritten bool, pseudo string) ([]string, int64) {
 	if len(g) == 0 {
 		return nil, 0
 	}
-	// An explicit '$' makes the operand an immediate ('$NOSPLIT' over the
-	// preprocessor's '$4'); the toolchain reads it as the same constant.
+	// The flags operand is a bare constant expression; the immediate
+	// spelling is the toolchain's "TEXT: expected integer constant".
 	if g[0].Kind == token.Dollar {
-		g = g[1:]
-		if len(g) == 0 {
-			return nil, 0
+		if p.expand {
+			found := "$"
+			if len(g) > 1 {
+				found += g[1].Text
+			}
+			p.errorf(g[0].Pos, "%s: expected integer constant; found %s", pseudo, found)
 		}
+		return nil, 0
 	}
 
 	sub := make([]token.Token, 0, len(g))