rust/tests/ui/fmt/format-args-capture-from-pm-first-arg-macro.stderr

error: there is no argument named `x`
  --> $DIR/format-args-capture-from-pm-first-arg-macro.rs:6:5
   |
LL |     format_string_proc_macro::bad_format_args_captures!();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: did you intend to capture a variable `x` from the surrounding scope?
   = note: to avoid ambiguity, `format_args!` cannot capture variables when the format string is expanded from a macro
   = note: this error originates in the macro `concat` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 1 previous error
Properly allow macro expanded `format_args` invocations to uses captures Originally, this was kinda half-allowed. There were some primitive checks in place that looked at the span to see whether the input was likely a literal. These "source literal" checks are needed because the spans created during `format_args` parsing only make sense when it is indeed a literal that was written in the source code directly. This is orthogonal to the restriction that the first argument must be a "direct literal", not being exanpanded from macros. This restriction was imposed by [RFC 2795] on the basis of being too confusing. But this was only concerned with the argument of the invocation being a literal, not whether it was a source literal (maybe in spirit it meant it being a source literal, this is not clear to me). Since the original check only really cared about source literals (which is good enough to deny the `format_args!(concat!())` example), macros expanding to `format_args` invocations were able to use implicit captures if they spanned the string in a way that lead back to a source string. The "source literal" checks were not strict enough and caused ICEs in certain cases (see # 106191 (the space is intended to avoid spammy backreferences)). So I tightened it up in # 106195 to really only work if it's a direct source literal. This caused the `indoc` crate to break. `indoc` transformed the source literal by removing whitespace, which made it not a "source literal" anymore (which is required to fix the ICE). But since `indoc` spanned the literal in ways that made the old check think that it's a literal, it was able to use implicit captures (which is useful and nice for the users of `indoc`). This commit properly seperates the previously introduced concepts of "source literal" and "direct literal" and therefore allows `indoc` invocations, which don't create "source literals" to use implicit captures again. [RFC 2795]: https://rust-lang.github.io/rfcs/2795-format-args-implicit-identifiers.html#macro-hygiene 2023-01-05 13:17:30 -06:00			error: there is no argument named `x`
			`--> $DIR/format-args-capture-from-pm-first-arg-macro.rs:6:5`
			`\|`
			`LL \| format_string_proc_macro::bad_format_args_captures!();`
			`\| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^`
			`\|`
			= note: did you intend to capture a variable `x` from the surrounding scope?
			= note: to avoid ambiguity, `format_args!` cannot capture variables when the format string is expanded from a macro
			= note: this error originates in the macro `concat` (in Nightly builds, run with -Z macro-backtrace for more info)

Show number in error message even for one error Co-authored-by: Adrian <adrian.iosdev@gmail.com> 2023-11-21 09:44:16 -06:00			`error: aborting due to 1 previous error`
Properly allow macro expanded `format_args` invocations to uses captures Originally, this was kinda half-allowed. There were some primitive checks in place that looked at the span to see whether the input was likely a literal. These "source literal" checks are needed because the spans created during `format_args` parsing only make sense when it is indeed a literal that was written in the source code directly. This is orthogonal to the restriction that the first argument must be a "direct literal", not being exanpanded from macros. This restriction was imposed by [RFC 2795] on the basis of being too confusing. But this was only concerned with the argument of the invocation being a literal, not whether it was a source literal (maybe in spirit it meant it being a source literal, this is not clear to me). Since the original check only really cared about source literals (which is good enough to deny the `format_args!(concat!())` example), macros expanding to `format_args` invocations were able to use implicit captures if they spanned the string in a way that lead back to a source string. The "source literal" checks were not strict enough and caused ICEs in certain cases (see # 106191 (the space is intended to avoid spammy backreferences)). So I tightened it up in # 106195 to really only work if it's a direct source literal. This caused the `indoc` crate to break. `indoc` transformed the source literal by removing whitespace, which made it not a "source literal" anymore (which is required to fix the ICE). But since `indoc` spanned the literal in ways that made the old check think that it's a literal, it was able to use implicit captures (which is useful and nice for the users of `indoc`). This commit properly seperates the previously introduced concepts of "source literal" and "direct literal" and therefore allows `indoc` invocations, which don't create "source literals" to use implicit captures again. [RFC 2795]: https://rust-lang.github.io/rfcs/2795-format-args-implicit-identifiers.html#macro-hygiene 2023-01-05 13:17:30 -06:00