Implement DesugaringKind::FormatLiteral

Author: mejrs

compiler/rustc_ast/src/format.rs

@@ -50,6 +50,14 @@ pub struct FormatArgs {
     ///
     /// Generally only useful for lints that care about the raw bytes the user wrote.
     pub uncooked_fmt_str: (LitKind, Symbol),
+    /// Was the format literal written in the source?
+    /// - `format!("boo")` => true,
+    /// - `format!(concat!("b", "o", "o"))` => false,
+    /// - `format!(include_str!("boo.txt"))` => false,
+    ///
+    /// If it wasn't written in the source then we have to be careful with spans pointing into it
+    /// and suggestions about rewriting it.
+    pub is_source_literal: bool,
 }
 
 /// A piece of a format template string.

compiler/rustc_ast/src/visit.rs

@@ -1389,7 +1389,7 @@ macro_rules! common_visitor_and_walkers {
 
         // FIXME: visit the template exhaustively.
         pub fn walk_format_args<$($lt,)? V: $Visitor$(<$lt>)?>(vis: &mut V, fmt: &$($lt)? $($mut)? FormatArgs) -> V::Result {
-            let FormatArgs { span, template: _, arguments, uncooked_fmt_str: _ } = fmt;
+            let FormatArgs { span, template: _, arguments, uncooked_fmt_str: _, is_source_literal: _ } = fmt;
             let args = $(${ignore($mut)} arguments.all_args_mut())? $(${ignore($lt)} arguments.all_args())? ;
             for FormatArgument { kind, expr } in args {
                 match kind {

compiler/rustc_ast_lowering/src/format.rs

@@ -6,7 +6,7 @@ use rustc_ast::*;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_hir as hir;
 use rustc_session::config::FmtDebug;
-use rustc_span::{Ident, Span, Symbol, sym};
+use rustc_span::{DesugaringKind, Ident, Span, Symbol, sym};
 
 use super::LoweringContext;
 
@@ -16,6 +16,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         // format_args!() had any arguments _before_ flattening/inlining.
         let allow_const = fmt.arguments.all_args().is_empty();
         let mut fmt = Cow::Borrowed(fmt);
+
+        let sp = self.mark_span_with_reason(
+            DesugaringKind::FormatLiteral { source: fmt.is_source_literal },
+            sp,
+            sp.ctxt().outer_expn_data().allow_internal_unstable,
+        );
+
         if self.tcx.sess.opts.unstable_opts.flatten_format_args {
             fmt = flatten_format_args(fmt);
             fmt = self.inline_literals(fmt);

compiler/rustc_builtin_macros/src/format.rs

@@ -606,6 +606,7 @@ fn make_format_args(
         template,
         arguments: args,
         uncooked_fmt_str,
+        is_source_literal,
     }))
 }
 

compiler/rustc_span/src/hygiene.rs

@@ -1213,6 +1213,17 @@ pub enum DesugaringKind {
     Contract,
     /// A pattern type range start/end
     PatTyRange,
+    /// A format literal.
+    FormatLiteral {
+        /// Was this format literal written in the source?
+        /// - `format!("boo")` => Yes,
+        /// - `format!(concat!("b", "o", "o"))` => No,
+        /// - `format!(include_str!("boo.txt"))` => No,
+        ///
+        /// If it wasn't written in the source then we have to be careful with suggestions about
+        /// rewriting it.
+        source: bool,
+    },
 }
 
 impl DesugaringKind {
@@ -1231,6 +1242,10 @@ impl DesugaringKind {
             DesugaringKind::BoundModifier => "trait bound modifier",
             DesugaringKind::Contract => "contract check",
             DesugaringKind::PatTyRange => "pattern type",
+            DesugaringKind::FormatLiteral { source: true } => "format string literal",
+            DesugaringKind::FormatLiteral { source: false } => {
+                "expression that expanded into a format string literal"
+            }
         }
     }
 
@@ -1250,6 +1265,7 @@ impl DesugaringKind {
             DesugaringKind::BoundModifier => value == "BoundModifier",
             DesugaringKind::Contract => value == "Contract",
             DesugaringKind::PatTyRange => value == "PatTyRange",
+            DesugaringKind::FormatLiteral { .. } => value == "FormatLiteral",
         }
     }
 }

compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs

@@ -2872,13 +2872,23 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                         _ => (),
                     }
                 }
-                let descr = format!("required by {a} bound in `{item_name}`");
-                if span.is_visible(sm) {
-                    let msg = format!("required by {this} in `{short_item_name}`");
-                    multispan.push_span_label(span, msg);
-                    err.span_note(multispan, descr);
+
+                // If this is from a format string literal desugaring,
+                // we've already said "required by this formatting parameter"
+                let is_in_fmt_lit = if let Some(s) = err.span.primary_span() {
+                    matches!(s.desugaring_kind(), Some(DesugaringKind::FormatLiteral { .. }))
                 } else {
-                    err.span_note(tcx.def_span(item_def_id), descr);
+                    false
+                };
+                if !is_in_fmt_lit {
+                    let descr = format!("required by {a} bound in `{item_name}`");
+                    if span.is_visible(sm) {
+                        let msg = format!("required by {this} in `{short_item_name}`");
+                        multispan.push_span_label(span, msg);
+                        err.span_note(multispan, descr);
+                    } else {
+                        err.span_note(tcx.def_span(item_def_id), descr);
+                    }
                 }
                 if let Some(note) = note {
                     err.note(note);
@@ -3977,7 +3987,15 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
             ) = expr.kind
             {
                 if Some(*span) != err.span.primary_span() {
-                    err.span_label(*span, "required by a bound introduced by this call");
+                    let msg = if span.is_desugaring(DesugaringKind::FormatLiteral { source: true })
+                    {
+                        "required by this formatting parameter"
+                    } else if span.is_desugaring(DesugaringKind::FormatLiteral { source: false }) {
+                        "required by a formatting parameter in this expression"
+                    } else {
+                        "required by a bound introduced by this call"
+                    };
+                    err.span_label(*span, msg);
                 }
             }
 

library/core/src/fmt/mod.rs

@@ -855,11 +855,13 @@ impl Display for Arguments<'_> {
 #[rustc_on_unimplemented(
     on(
         crate_local,
-        label = "`{Self}` cannot be formatted using `{{:?}}`",
         note = "add `#[derive(Debug)]` to `{Self}` or manually `impl {This} for {Self}`"
     ),
-    message = "`{Self}` doesn't implement `{This}`",
-    label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{This}`"
+    on(
+        from_desugaring = "FormatLiteral",
+        label = "`{Self}` cannot be formatted using `{{:?}}` because it doesn't implement `{This}`"
+    ),
+    message = "`{Self}` doesn't implement `{This}`"
 )]
 #[doc(alias = "{:?}")]
 #[rustc_diagnostic_item = "Debug"]
@@ -986,11 +988,14 @@ pub use macros::Debug;
         any(Self = "std::path::Path", Self = "std::path::PathBuf"),
         label = "`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
         note = "call `.display()` or `.to_string_lossy()` to safely print paths, \
-                as they may contain non-Unicode data"
+                as they may contain non-Unicode data",
+    ),
+    on(
+        from_desugaring = "FormatLiteral",
+        note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead",
+        label = "`{Self}` cannot be formatted with the default formatter",
     ),
-    message = "`{Self}` doesn't implement `{This}`",
-    label = "`{Self}` cannot be formatted with the default formatter",
-    note = "in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead"
+    message = "`{Self}` doesn't implement `{This}`"
 )]
 #[doc(alias = "{}")]
 #[rustc_diagnostic_item = "Display"]

tests/ui/argument-suggestions/issue-100154.stderr

@@ -17,10 +17,8 @@ error[E0277]: `()` doesn't implement `std::fmt::Display`
   --> $DIR/issue-100154.rs:4:11
    |
 LL |     foo::<()>(());
-   |           ^^ `()` cannot be formatted with the default formatter
+   |           ^^ the trait `std::fmt::Display` is not implemented for `()`
    |
-   = help: the trait `std::fmt::Display` is not implemented for `()`
-   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `foo`
   --> $DIR/issue-100154.rs:1:16
    |

tests/ui/associated-types/defaults-unsound-62211-1.current.stderr

@@ -2,9 +2,8 @@ error[E0277]: `Self` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-1.rs:24:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-   |                                                                                                ^^^^ `Self` cannot be formatted with the default formatter
+   |                                                                                                ^^^^ the trait `std::fmt::Display` is not implemented for `Self`
    |
-   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `UncheckedCopy::Output`
   --> $DIR/defaults-unsound-62211-1.rs:24:86
    |

tests/ui/associated-types/defaults-unsound-62211-1.next.stderr

@@ -2,9 +2,8 @@ error[E0277]: `Self` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-1.rs:24:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
-   |                                                                                                ^^^^ `Self` cannot be formatted with the default formatter
+   |                                                                                                ^^^^ the trait `std::fmt::Display` is not implemented for `Self`
    |
-   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `UncheckedCopy::Output`
   --> $DIR/defaults-unsound-62211-1.rs:24:86
    |