Don't suggest to match list expressions using '=='

Noticed by Jonathan Perkin in devel/ncurses, where pkglint wrongly
suggested replacing ${USE_NCURSES:Mwide} with ${USE_NCURSES} == wide.

v23/mkcondchecker.go

@@ -145,6 +145,8 @@ func (ck *MkCondChecker) checkEmpty(expr *MkExpr, fromEmpty bool, neg bool) {
 	s.SimplifyExpr(expr, fromEmpty, neg)
 }
 
+// checkEmptyExpr warns about 'empty(${VARNAME:Mpattern})', which should be
+// 'empty(VARNAME:Mpattern)' instead, without the '${...}'.
 func (ck *MkCondChecker) checkEmptyExpr(expr *MkExpr, neg bool) {
 	if !matches(expr.varname, `^\$.*:[MN]`) {
 		return
@@ -158,7 +160,7 @@ func (ck *MkCondChecker) checkEmptyExpr(expr *MkExpr, neg bool) {
 			"you should write either of the following:",
 			"",
 			"\t!empty(VARNAME:Mpattern)",
-			"\t${VARNAME:Mpattern} != \"\"",
+			"\t${VARNAME:U:Mpattern} != \"\"",
 			"",
 			"If the pattern cannot match the number zero,",
 			"you can omit the '!= \"\"', resulting in:",
@@ -180,6 +182,8 @@ func (ck *MkCondChecker) checkEmptyExpr(expr *MkExpr, neg bool) {
 	}
 }
 
+// checkEmptyType warns if there is a ':M' modifier in which the pattern
+// doesn't match the type of the expression.
 func (ck *MkCondChecker) checkEmptyType(expr *MkExpr) {
 	for _, modifier := range expr.modifiers {
 		ok, _, pattern, _ := modifier.MatchMatch()

v23/mkcondsimplifier.go

@@ -24,7 +24,10 @@ func (s *MkCondSimplifier) SimplifyExpr(expr *MkExpr, fromEmpty bool, neg bool)
 		return
 	}
 	s.simplifyMatch(expr, fromEmpty, neg)
-	s.simplifyWord(expr, fromEmpty, neg)
+	vartype := G.Pkgsrc.VariableType(s.MkLines, expr.varname)
+	if vartype != nil && !vartype.IsList() && vartype.basicType != BtUnknown {
+		s.simplifyWord(expr, fromEmpty, neg)
+	}
 }
 
 // simplifyWord simplifies a condition like '${VAR:Mword}' in the common case

v23/mkcondsimplifier_test.go

@@ -834,10 +834,6 @@ func (s *Suite) Test_MkCondSimplifier_simplifyWord__list_and_unknown(c *check.C)
 		"WARN: filename.mk:10: LIST_OF_WORDS should be matched "+
 			"against \"[yY][eE][sS]\" or \"[nN][oO]\", "+
 			"not \"yes\".",
-		// FIXME: UNKNOWN could be a list as well.
-		"NOTE: filename.mk:12: UNKNOWN can be compared "+
-			"using the simpler \"${UNKNOWN} == yes\" "+
-			"instead of matching against \":Myes\".",
 	)
 }
 

v23/vartype.go

@@ -202,6 +202,9 @@ func (perms ACLPermissions) HumanString() string {
 		condStr(perms.Contains(aclpUse), "used", ""))
 }
 
+// IsList returns whether the type is a list of something.
+// A return value of false doesn't mean a single-word type,
+// it could also be BtUnknown.
 func (vt *Vartype) IsList() bool                { return vt.options&List != 0 }
 func (vt *Vartype) IsGuessed() bool             { return vt.options&Guessed != 0 }
 func (vt *Vartype) IsPackageSettable() bool     { return vt.options&PackageSettable != 0 }