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

lint/lint.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 
 	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
+	"sourcedock.dev/petrbalvin/gasm-devkit/asm"
 	"sourcedock.dev/petrbalvin/gasm-devkit/ast"
 	"sourcedock.dev/petrbalvin/gasm-devkit/token"
 )
@@ -78,6 +79,8 @@ const (
 	CodeStackImbalance        = "stack-imbalance"
 	CodeRegisterWidthMismatch = "register-width-mismatch"
 	CodeABI0RegisterArgs      = "abi0-register-args"
+	CodeNonportableRegister   = "nonportable-register-name"
+	CodeUnencodable           = "unencodable-instruction"
 )
 
 // knownTextFlags are the flags recognised by the Go assembler's textflag.h.
@@ -282,6 +285,18 @@ func lintText(t *ast.Text, tab *arch.Table, archKnown bool, cfg Config, macros m
 						Code:     CodeUnknownInstr,
 						Message:  fmt.Sprintf("unknown %s instruction %q", cfg.Arch, mnem),
 					})
+				} else if cfg.Arch == arch.AMD64 && !cfg.Disable[CodeUnencodable] && !asm.Encodable(upper) {
+					// Known to the architecture table but missing from the
+					// encoder: the file parses everywhere and then fails at
+					// assembly time.  Flag it at lint so the gap is visible
+					// in the editor, and so the audit can close it.
+					out = append(out, Diagnostic{
+						Pos:      st.Mnemonic.Pos,
+						End:      st.Mnemonic.End,
+						Severity: Warning,
+						Code:     CodeUnencodable,
+						Message:  fmt.Sprintf("instruction %q is known but the encoder cannot assemble it yet", mnem),
+					})
 				}
 			}