Statement macros are now treated somewhat like item macros, in that a statement macro can now expand into a series of statements, rather than just a single statement.
This allows statement macros to be nested inside other kinds of macros and expand properly, where previously the expansion would only work when no nesting was present.
See:
- `src/test/run-pass/macro-stmt_macro_in_expr_macro.rs`
- `src/test/run-pass/macro-nested_stmt_macro.rs`
This changes the interface of the MacResult trait. make_stmt has become make_stmts and now returns a vector, rather than a single item. Plugin writers who were implementing MacResult will have breakage, as well as anyone using MacEager::stmt.
See:
- `src/libsyntax/ext/base.rs`
This also causes a minor difference in behavior to the diagnostics produced by certain malformed macros.
See:
- `src/test/compile-fail/macro-incomplete-parse.rs`
Statement macros are now treated somewhat like item macros, in that a
statement macro can now expand into a series of statements, rather than
just a single statement.
This allows statement macros to be nested inside other kinds of macros and
expand properly, where previously the expansion would only work when no
nesting was present.
See: src/test/run-pass/macro-stmt_macro_in_expr_macro.rs
src/test/run-pass/macro-nested_stmt_macro.rs
This changes the interface of the MacResult trait. make_stmt has become
make_stmts and now returns a vector, rather than a single item. Plugin
writers who were implementing MacResult will have breakage, as well as
anyone using MacEager::stmt.
See: src/libsyntax/ext/base.rs
This also causes a minor difference in behavior to the diagnostics
produced by certain malformed macros.
See: src/test/compile-fail/macro-incomplete-parse.rs
followed by a semicolon.
This allows code like `vec![1i, 2, 3].len();` to work.
This breaks code that uses macros as statements without putting
semicolons after them, such as:
fn main() {
...
assert!(a == b)
assert!(c == d)
println(...);
}
It also breaks code that uses macros as items without semicolons:
local_data_key!(foo)
fn main() {
println("hello world")
}
Add semicolons to fix this code. Those two examples can be fixed as
follows:
fn main() {
...
assert!(a == b);
assert!(c == d);
println(...);
}
local_data_key!(foo);
fn main() {
println("hello world")
}
RFC #378.
Closes#18635.
[breaking-change]
That is, only a single expression or item gets parsed, so if there are
any extra tokens (e.g. the start of another item/expression) the user
should be told, rather than silently dropping them.
An example:
macro_rules! foo {
() => {
println("hi");
println("bye);
}
}
would expand to just `println("hi")`, which is almost certainly not
what the programmer wanted.
Fixes#8012.
