feat: Implicit format args support

crates/hir-def/src/body.rs

@@ -95,6 +95,8 @@ pub struct BodySourceMap {
     field_map_back: FxHashMap<ExprId, FieldSource>,
     pat_field_map_back: FxHashMap<PatId, PatFieldSource>,
 
+    format_args_template_map: FxHashMap<ExprId, Vec<(syntax::TextRange, Name)>>,
+
     expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,
 
     /// Diagnostics accumulated during body lowering. These contain `AstPtr`s and so are stored in
@@ -387,6 +389,14 @@ impl BodySourceMap {
         self.expr_map.get(&src).copied()
     }
 
+    pub fn implicit_format_args(
+        &self,
+        node: InFile<&ast::FormatArgsExpr>,
+    ) -> Option<&[(syntax::TextRange, Name)]> {
+        let src = node.map(AstPtr::new).map(AstPtr::upcast::<ast::Expr>);
+        self.format_args_template_map.get(self.expr_map.get(&src)?).map(std::ops::Deref::deref)
+    }
+
     /// Get a reference to the body source map's diagnostics.
     pub fn diagnostics(&self) -> &[BodyDiagnostic] {
         &self.diagnostics
@@ -403,8 +413,10 @@ impl BodySourceMap {
             field_map_back,
             pat_field_map_back,
             expansions,
+            format_args_template_map,
             diagnostics,
         } = self;
+        format_args_template_map.shrink_to_fit();
         expr_map.shrink_to_fit();
         expr_map_back.shrink_to_fit();
         pat_map.shrink_to_fit();

crates/hir-def/src/body/lower.rs

@@ -1597,12 +1597,20 @@ impl ExprCollector<'_> {
         });
         let template = f.template();
         let fmt_snippet = template.as_ref().map(ToString::to_string);
+        let mut mappings = vec![];
         let fmt = match template.and_then(|it| self.expand_macros_to_string(it)) {
-            Some((s, is_direct_literal)) => {
-                format_args::parse(&s, fmt_snippet, args, is_direct_literal, |name| {
-                    self.alloc_expr_desugared(Expr::Path(Path::from(name)))
-                })
-            }
+            Some((s, is_direct_literal)) => format_args::parse(
+                &s,
+                fmt_snippet,
+                args,
+                is_direct_literal,
+                |name| self.alloc_expr_desugared(Expr::Path(Path::from(name))),
+                |name, span| {
+                    if let Some(span) = span {
+                        mappings.push((span, name.clone()))
+                    }
+                },
+            ),
             None => FormatArgs { template: Default::default(), arguments: args.finish() },
         };
 
@@ -1746,14 +1754,16 @@ impl ExprCollector<'_> {
             tail: Some(unsafe_arg_new),
         });
 
-        self.alloc_expr(
+        let idx = self.alloc_expr(
             Expr::Call {
                 callee: new_v1_formatted,
                 args: Box::new([lit_pieces, args, format_options, unsafe_arg_new]),
                 is_assignee_expr: false,
             },
             syntax_ptr,
-        )
+        );
+        self.source_map.format_args_template_map.insert(idx, mappings);
+        idx
     }
 
     /// Generate a hir expression for a format_args placeholder specification.

crates/hir-def/src/body/tests.rs

@@ -160,7 +160,7 @@ fn main() {
             let count = 10;
             builtin#lang(Arguments::new_v1_formatted)(
                 &[
-                    "\"hello ", " ", " friends, we ", " ", "", "\"",
+                    "hello ", " ", " friends, we ", " ", "",
                 ],
                 &[
                     builtin#lang(Argument::new_display)(
@@ -261,7 +261,7 @@ impl SsrError {
             _ = $crate::error::SsrError::new(
                 builtin#lang(Arguments::new_v1_formatted)(
                     &[
-                        "\"Failed to resolve path `", "`\"",
+                        "Failed to resolve path `", "`",
                     ],
                     &[
                         builtin#lang(Argument::new_display)(
@@ -320,7 +320,7 @@ fn f() {
             $crate::panicking::panic_fmt(
                 builtin#lang(Arguments::new_v1_formatted)(
                     &[
-                        "\"cc\"",
+                        "cc",
                     ],
                     &[],
                     &[],

crates/hir-def/src/hir/format_args.rs

@@ -5,7 +5,7 @@ use hir_expand::name::Name;
 use rustc_dependencies::parse_format as parse;
 use syntax::{
     ast::{self, IsString},
-    AstToken, SmolStr, TextRange,
+    SmolStr, TextRange, TextSize,
 };
 
 use crate::hir::ExprId;
@@ -170,15 +170,18 @@ pub(crate) fn parse(
     mut args: FormatArgumentsCollector,
     is_direct_literal: bool,
     mut synth: impl FnMut(Name) -> ExprId,
+    mut record_usage: impl FnMut(Name, Option<TextRange>),
 ) -> FormatArgs {
-    let text = s.text();
+    let text = s.text_without_quotes();
     let str_style = match s.quote_offsets() {
         Some(offsets) => {
             let raw = u32::from(offsets.quotes.0.len()) - 1;
-            (raw != 0).then_some(raw as usize)
+            // subtract 1 for the `r` prefix
+            (raw != 0).then(|| raw as usize - 1)
         }
         None => None,
     };
+
     let mut parser =
         parse::Parser::new(text, str_style, fmt_snippet, false, parse::ParseMode::Format);
 
@@ -199,6 +202,7 @@ pub(crate) fn parse(
     let to_span = |inner_span: parse::InnerSpan| {
         is_source_literal.then(|| {
             TextRange::new(inner_span.start.try_into().unwrap(), inner_span.end.try_into().unwrap())
+                - TextSize::from(str_style.map(|it| it + 1).unwrap_or(0) as u32 + 1)
         })
     };
 
@@ -230,9 +234,10 @@ pub(crate) fn parse(
                     Err(index)
                 }
             }
-            ArgRef::Name(name, _span) => {
+            ArgRef::Name(name, span) => {
                 let name = Name::new_text_dont_use(SmolStr::new(name));
                 if let Some((index, _)) = args.by_name(&name) {
+                    record_usage(name, span);
                     // Name found in `args`, so we resolve it to its index.
                     if index < args.explicit_args().len() {
                         // Mark it as used, if it was an explicit argument.
@@ -246,6 +251,7 @@ pub(crate) fn parse(
                         // disabled (see RFC #2795)
                         // FIXME: Diagnose
                     }
+                    record_usage(name.clone(), span);
                     Ok(args.add(FormatArgument {
                         kind: FormatArgumentKind::Captured(name.clone()),
                         // FIXME: This is problematic, we might want to synthesize a dummy

crates/hir-expand/src/lib.rs

@@ -629,8 +629,6 @@ impl ExpansionInfo {
     pub fn map_range_down<'a>(
         &'a self,
         span: SpanData,
-        // FIXME: use this for range mapping, so that we can resolve inline format args
-        _relative_token_offset: Option<TextSize>,
     ) -> Option<impl Iterator<Item = InMacroFile<SyntaxToken>> + 'a> {
         let tokens = self
             .exp_map

crates/hir/src/lib.rs

@@ -92,7 +92,9 @@ pub use crate::{
     attrs::{resolve_doc_path_on, HasAttrs},
     diagnostics::*,
     has_source::HasSource,
-    semantics::{PathResolution, Semantics, SemanticsScope, TypeInfo, VisibleTraits},
+    semantics::{
+        DescendPreference, PathResolution, Semantics, SemanticsScope, TypeInfo, VisibleTraits,
+    },
 };
 
 // Be careful with these re-exports.