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cond-undef-lint.mk revision 1.3 
      1 # $NetBSD: cond-undef-lint.mk,v 1.3 2020/11/15 14:58:14 rillig Exp $
      2 #
      3 # Tests for defined and undefined variables in .if conditions, in lint mode.
      4 #
      5 # As of 2020-09-14, lint mode contains experimental code for printing
      6 # accurate error messages in case of undefined variables, instead of the
      7 # wrong "Malformed condition".
      8 #
      9 # See also:
     10 #	opt-debug-lint.mk
     11 
     12 .MAKEFLAGS: -dL
     13 
     14 # DEF is defined, UNDEF is not.
     15 DEF=		defined
     16 
     17 # An expression based on a defined variable is fine.
     18 .if !${DEF}
     19 .  error
     20 .endif
     21 
     22 # Since the condition fails to evaluate, neither of the branches is taken.
     23 .if ${UNDEF}
     24 .  error
     25 .else
     26 .  error
     27 .endif
     28 
     29 # The variable name depends on the undefined variable, which is probably a
     30 # mistake.  The variable UNDEF, as used here, can be easily turned into
     31 # an expression that is always defined, using the :U modifier.
     32 #
     33 # The outer expression does not generate an error message since there was
     34 # already an error evaluating this variable's name.
     35 #
     36 # TODO: Suppress the error message "Variable VAR. is undefined".  That part
     37 # of the expression must not be evaluated at all.
     38 .if ${VAR.${UNDEF}}
     39 .  error
     40 .else
     41 .  error
     42 .endif
     43 
     44 # The variable VAR.defined is not defined and thus generates an error message.
     45 #
     46 # TODO: This pattern looks a lot like CFLAGS.${OPSYS}, which is at least
     47 # debatable.  Or would any practical use of CFLAGS.${OPSYS} be via an indirect
     48 # expression, as in the next example?
     49 .if ${VAR.${DEF}}
     50 .  error
     51 .else
     52 .  error
     53 .endif
     54 
     55 
     56 # Variables that are referenced indirectly may be undefined in a condition.
     57 #
     58 # A practical example for this is CFLAGS, which consists of CWARNS, COPTS
     59 # and a few others.  Just because these nested variables are not defined,
     60 # this does not make the condition invalid.
     61 #
     62 # The crucial point is that at the point where the variable appears in the
     63 # condition, there is no way to influence the definedness of the nested
     64 # variables.  In particular, there is no modifier that would turn undefined
     65 # nested variables into empty strings, as an equivalent to the :U modifier.
     66 INDIRECT=	${NESTED_UNDEF} ${NESTED_DEF}
     67 NESTED_DEF=	nested-defined
     68 
     69 # Since NESTED_UNDEF is not controllable at this point, it must not generate
     70 # an error message, and it doesn't do so, since 2020-09-14.
     71 .if !${INDIRECT}
     72 .  error
     73 .endif
     74