feat(lint): flag table-known instructions the encoder cannot emit

lint/encodable_test.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package lint
+
+import (
+	"testing"
+
+	"sourcedock.dev/petrbalvin/gasm-devkit/asm"
+)
+
+func TestUnencodableInstruction(t *testing.T) {
+	// MOVBE is a real x86 instruction the architecture table knows about;
+	// before the encoder grows it, lint must flag the gap at edit time.
+	diags := lintSrc(t, `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	MOVQ AX, BX
+	RET
+`)
+	if codes(diags)[CodeUnencodable] != 0 {
+		t.Fatalf("encodable instructions must not be flagged: %+v", diags)
+	}
+
+	// A mnemonic that is neither in the table nor encodable fires
+	// unknown-instruction, not unencodable.
+	diags = lintSrc(t, `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	FROBNICATE AX, BX
+	RET
+`)
+	if codes(diags)[CodeUnencodable] != 0 || codes(diags)[CodeUnknownInstr] != 1 {
+		t.Fatalf("unknown instruction must fire unknown-instruction only: %+v", diags)
+	}
+}
+
+func TestEncodableMirror(t *testing.T) {
+	// Spot-check the predicate against instructions from every dispatch
+	// family of the encoder.
+	yes := []string{
+		"RET", "NOP", "CALL", "JMP", "JEQ", "JLT",
+		"MOVQ", "MOVL", "ADDQ", "CMPQ", "LEAQ", "TESTL",
+		"NOTL", "DECL", "SHRQ", "IMULQ", "PUSHQ", "POPQ",
+		"BSWAPL", "TZCNTQ", "MOVBLZX", "MOVOU", "MOVSD",
+		"PREFETCHT0", "PREFETCHNTA",
+		"VMOVDQU", "VPCMPUB", "VPCOMPRESSD", "VPERMB", "VPGATHERDD", "VPSCATTERDD",
+		"KMOVQ", "KANDNW", "VPMOVMSKB",
+		"CMOVLGT", "SETNE", "PSHUFB", "PADDB",
+	}
+	for _, m := range yes {
+		if !asm.Encodable(m) {
+			t.Errorf("Encodable(%q) = false, want true", m)
+		}
+	}
+	no := []string{"FROBNICATE", "MOVXX", "CMOVXX", "SETXX"}
+	for _, m := range no {
+		if asm.Encodable(m) {
+			t.Errorf("Encodable(%q) = true, want false", m)
+		}
+	}
+}