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Make format_args!("literal") const.
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6 files changed

+62
-29
lines changed

6 files changed

+62
-29
lines changed

‎compiler/rustc_builtin_macros/src/format.rs

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -761,6 +761,7 @@ impl<'a, 'b> Context<'a, 'b> {
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/// Actually builds the expression which the format_args! block will be
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/// expanded to.
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fn into_expr(self) -> P<ast::Expr> {
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let is_literal = self.str_pieces.len() == 1 && self.args.is_empty();
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let mut locals =
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Vec::with_capacity((0..self.args.len()).map(|i| self.arg_unique_types[i].len()).sum());
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let mut counts = Vec::with_capacity(self.count_args.len());
@@ -846,7 +847,9 @@ impl<'a, 'b> Context<'a, 'b> {
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let args_slice = self.ecx.expr_addr_of(self.macsp, result);
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// Now create the fmt::Arguments struct with all our locals we created.
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let (fn_name, fn_args) = if self.all_pieces_simple {
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let (fn_name, fn_args) = if is_literal {
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("new_literal", vec![pieces])
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} else if self.all_pieces_simple {
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("new_v1", vec![pieces, args_slice])
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} else {
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// Build up the static array which will store our precompiled

‎library/core/src/fmt/mod.rs

Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -332,6 +332,15 @@ enum FlagV1 {
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}
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impl<'a> Arguments<'a> {
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/// When using the format_args!() macro, this function is used to generate the
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/// Arguments structure in case it's just a single string literal.
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#[doc(hidden)]
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#[inline]
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#[unstable(feature = "fmt_internals", reason = "internal to format_args!", issue = "none")]
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pub const fn new_literal(pieces: &'a [&'static str; 1]) -> Arguments<'a> {
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Arguments { pieces, fmt: None, args: &[] }
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}
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/// When using the format_args!() macro, this function is used to generate the
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/// Arguments structure.
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#[doc(hidden)]

‎src/test/pretty/dollar-crate.pp

Lines changed: 1 addition & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -9,10 +9,5 @@
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// pp-exact:dollar-crate.pp
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fn main() {
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{
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::std::io::_print(::core::fmt::Arguments::new_v1(&["rust\n"],
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&match () {
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() => [],
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}));
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};
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{ ::std::io::_print(::core::fmt::Arguments::new_literal(&["rust\n"])); };
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}

‎src/test/pretty/issue-4264.pp

Lines changed: 8 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -32,29 +32,15 @@
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({
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let res =
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((::alloc::fmt::format as
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for<'r> fn(Arguments<'r>) -> String {format})(((::core::fmt::Arguments::new_v1
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for<'r> fn(Arguments<'r>) -> String {format})(((::core::fmt::Arguments::new_literal
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as
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fn(&[&'static str], &[ArgumentV1]) -> Arguments {Arguments::new_v1})((&([("test"
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as
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&str)]
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as
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[&str; 1])
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as
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&[&str; 1]),
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(&(match (()
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as
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())
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{
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()
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=>
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([]
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as
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[ArgumentV1; 0]),
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}
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as
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[ArgumentV1; 0])
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as
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&[ArgumentV1; 0]))
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fn(&[&'static str; 1]) -> Arguments {Arguments::new_literal})((&([("test"
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as
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&str)]
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as
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[&str; 1])
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as
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&[&str; 1]))
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as
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Arguments))
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as String);

‎src/test/ui/consts/const-eval/format_args.rs

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
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#![crate_type = "lib"]
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const A: std::fmt::Arguments = format_args!("literal");
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const B: std::fmt::Arguments = format_args!("{}", 123);
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//~^ ERROR calls in constants are limited to
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//~| ERROR calls in constants are limited to
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//~| ERROR temporary value

‎src/test/ui/consts/const-eval/format_args.stderr

Lines changed: 32 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,32 @@
1+
error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
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--> $DIR/format_args.rs:5:32
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|
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LL | const B: std::fmt::Arguments = format_args!("{}", 123);
5+
| ^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
8+
9+
error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
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--> $DIR/format_args.rs:5:32
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|
12+
LL | const B: std::fmt::Arguments = format_args!("{}", 123);
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| ^^^^^^^^^^^^^^^^^^^^^^^
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|
15+
= note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
16+
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error[E0716]: temporary value dropped while borrowed
18+
--> $DIR/format_args.rs:5:32
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|
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LL | const B: std::fmt::Arguments = format_args!("{}", 123);
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| ^^^^^^^^^^^^^^^^^^^^^^-
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| | |
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| | temporary value is freed at the end of this statement
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| creates a temporary which is freed while still in use
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| using this value as a constant requires that borrow lasts for `'static`
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|
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= note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
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error: aborting due to 3 previous errors
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Some errors have detailed explanations: E0015, E0716.
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For more information about an error, try `rustc --explain E0015`.

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