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libexpr: deprecate the bogus "or"-as-variable

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As a prelude to making "or" work like a normal variable, emit a warning
any time the "fn or" production is used in a context that will change
how it is parsed when that production is refactored.

In detail: in the future, OR_KW will be moved to expr_simple, and the
cursed ExprCall production that is currently part of the expr_select
nonterminal will be generated "normally" in expr_app instead. Any
productions that accept an expr_select will be affected, except for the
expr_app nonterminal itself (because, while expr_app has a production
accepting a bare expr_select, its other production will continue to
accept "fn or" expressions). So all we need to do is emit an appropriate
warning when an expr_simple representing a cursed ExprCall is accepted
in one of those productions without first going through expr_app.

As the warning message describes, users can suppress the warning by
wrapping their problematic "fn or" expressions in parentheses. For
example, "f g or" can be made future-proof by rewriting it as
"f (g or)"; similarly "[ x y or ]" can be rewritten as "[ x (y or) ]",
etc. The parentheses preserve the current grouping behavior, as in the
future "f g or" will be parsed as "(f g) or", just like
"f g anything-else" is grouped. (Mechanically, this suppresses the
warning because the problem ExprCalls go through the
"expr_app : expr_select" production, which resets the cursed status on
the ExprCall.)
This commit is contained in:
Ryan Hendrickson 2024-09-20 15:57:36 -04:00
parent 68ba6ff470
commit da332d678e
6 changed files with 79 additions and 8 deletions
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12
src/libexpr/nixexpr.hh
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@ -96,6 +96,10 @@ struct Expr
virtual void setName(Symbol name);
virtual void setDocComment(DocComment docComment) { };
virtual PosIdx getPos() const { return noPos; }
// These are temporary methods to be used only in parser.y
virtual void resetCursedOr() { };
virtual void warnIfCursedOr(const SymbolTable & symbols, const PosTable & positions) { };
};
#define COMMON_METHODS \
@ -354,10 +358,16 @@ struct ExprCall : Expr
Expr * fun;
std::vector<Expr *> args;
PosIdx pos;
std::optional<PosIdx> cursedOrEndPos; // used during parsing to warn about https://github.com/NixOS/nix/issues/11118
ExprCall(const PosIdx & pos, Expr * fun, std::vector<Expr *> && args)
: fun(fun), args(args), pos(pos)
: fun(fun), args(args), pos(pos), cursedOrEndPos({})
{ }
ExprCall(const PosIdx & pos, Expr * fun, std::vector<Expr *> && args, PosIdx && cursedOrEndPos)
: fun(fun), args(args), pos(pos), cursedOrEndPos(cursedOrEndPos)
{ }
PosIdx getPos() const override { return pos; }
virtual void resetCursedOr() override;
virtual void warnIfCursedOr(const SymbolTable & symbols, const PosTable & positions) override;
COMMON_METHODS
};