Revert "Improve heuristics whether `format_args` string is a source literal"

This reverts commit e6c02aad9345925cfed74f86b414c4d0715d381b.

Keeps the code improvements from the PR and the test (as a known-bug).

5 files changed, 32 insertions, 56 deletions

diff --git a/compiler/rustc_parse_format/src/lib.rs b/compiler/rustc_parse_format/src/lib.rs
index 1eb227503f2..7b016cadac3 100644
--- a/compiler/rustc_parse_format/src/lib.rs
+++ b/compiler/rustc_parse_format/src/lib.rs
@@ -20,7 +20,6 @@ pub use Flag::*;
 pub use Piece::*;
 pub use Position::*;
 
-use rustc_lexer::unescape;
 use std::iter;
 use std::str;
 use std::string;
@@ -314,11 +313,12 @@ impl<'a> Parser<'a> {
         append_newline: bool,
         mode: ParseMode,
     ) -> Parser<'a> {
-        let input_string_kind = find_width_map_from_snippet(s, snippet, style);
+        let input_string_kind = find_width_map_from_snippet(snippet, style);
         let (width_map, is_literal) = match input_string_kind {
             InputStringKind::Literal { width_mappings } => (width_mappings, true),
             InputStringKind::NotALiteral => (Vec::new(), false),
         };
+
         Parser {
             mode,
             input: s,
@@ -856,7 +856,6 @@ impl<'a> Parser<'a> {
 /// written code (code snippet) and the `InternedString` that gets processed in the `Parser`
 /// in order to properly synthesise the intra-string `Span`s for error diagnostics.
 fn find_width_map_from_snippet(
-    input: &str,
     snippet: Option<string::String>,
     str_style: Option<usize>,
 ) -> InputStringKind {
@@ -869,27 +868,8 @@ fn find_width_map_from_snippet(
         return InputStringKind::Literal { width_mappings: Vec::new() };
     }
 
-    // Strip quotes.
     let snippet = &snippet[1..snippet.len() - 1];
 
-    // Macros like `println` add a newline at the end. That technically doens't make them "literals" anymore, but it's fine
-    // since we will never need to point our spans there, so we lie about it here by ignoring it.
-    // Since there might actually be newlines in the source code, we need to normalize away all trailing newlines.
-    // If we only trimmed it off the input, `format!("\n")` would cause a mismatch as here we they actually match up.
-    // Alternatively, we could just count the trailing newlines and only trim one from the input if they don't match up.
-    let input_no_nl = input.trim_end_matches('\n');
-    let Ok(unescaped) = unescape_string(snippet) else {
-        return InputStringKind::NotALiteral;
-    };
-
-    let unescaped_no_nl = unescaped.trim_end_matches('\n');
-
-    if unescaped_no_nl != input_no_nl {
-        // The source string that we're pointing at isn't our input, so spans pointing at it will be incorrect.
-        // This can for example happen with proc macros that respan generated literals.
-        return InputStringKind::NotALiteral;
-    }
-
     let mut s = snippet.char_indices();
     let mut width_mappings = vec![];
     while let Some((pos, c)) = s.next() {
@@ -972,19 +952,6 @@ fn find_width_map_from_snippet(
     InputStringKind::Literal { width_mappings }
 }
 
-fn unescape_string(string: &str) -> Result<string::String, unescape::EscapeError> {
-    let mut buf = string::String::new();
-    let mut error = Ok(());
-    unescape::unescape_literal(string, unescape::Mode::Str, &mut |_, unescaped_char| {
-        match unescaped_char {
-            Ok(c) => buf.push(c),
-            Err(err) => error = Err(err),
-        }
-    });
-
-    error.map(|_| buf)
-}
-
 // Assert a reasonable size for `Piece`
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 rustc_data_structures::static_assert_size!(Piece<'_>, 16);
diff --git a/tests/ui/fmt/auxiliary/format-string-proc-macro.rs b/tests/ui/fmt/auxiliary/format-string-proc-macro.rs
index 539c8fb27b3..1b7ef93f41d 100644
--- a/tests/ui/fmt/auxiliary/format-string-proc-macro.rs
+++ b/tests/ui/fmt/auxiliary/format-string-proc-macro.rs
@@ -28,6 +28,7 @@ pub fn err_with_input_span(input: TokenStream) -> TokenStream {
     TokenStream::from(TokenTree::Literal(lit))
 }
 
+
 #[proc_macro]
 pub fn respan_to_invalid_format_literal(input: TokenStream) -> TokenStream {
     let mut s = Literal::string("{");
@@ -38,3 +39,14 @@ pub fn respan_to_invalid_format_literal(input: TokenStream) -> TokenStream {
         TokenTree::from(Group::new(Delimiter::Parenthesis, TokenTree::from(s).into())),
     ])
 }
+
+#[proc_macro]
+pub fn capture_a_with_prepended_space_preserve_span(input: TokenStream) -> TokenStream {
+    let mut s = Literal::string(" {a}");
+    s.set_span(input.into_iter().next().unwrap().span());
+    TokenStream::from_iter([
+        TokenTree::from(Ident::new("format", Span::call_site())),
+        TokenTree::from(Punct::new('!', Spacing::Alone)),
+        TokenTree::from(Group::new(Delimiter::Parenthesis, TokenTree::from(s).into())),
+    ])
+}
diff --git a/tests/ui/fmt/indoc-issue-106408.rs b/tests/ui/fmt/indoc-issue-106408.rs
new file mode 100644
index 00000000000..e4e3093b590
--- /dev/null
+++ b/tests/ui/fmt/indoc-issue-106408.rs
@@ -0,0 +1,9 @@
+// aux-build:format-string-proc-macro.rs
+// check-pass
+
+extern crate format_string_proc_macro;
+
+fn main() {
+    let a = 0;
+    format_string_proc_macro::capture_a_with_prepended_space_preserve_span!("{a}");
+}
diff --git a/tests/ui/fmt/respanned-literal-issue-106191.rs b/tests/ui/fmt/respanned-literal-issue-106191.rs
index 44642a10fc0..bb741c0ef93 100644
--- a/tests/ui/fmt/respanned-literal-issue-106191.rs
+++ b/tests/ui/fmt/respanned-literal-issue-106191.rs
@@ -1,10 +1,15 @@
 // aux-build:format-string-proc-macro.rs
+// check-fail
+// known-bug: #106191
+// unset-rustc-env:RUST_BACKTRACE
+// had to be reverted
+// error-pattern:internal compiler error
+// failure-status:101
+// dont-check-compiler-stderr
 
 extern crate format_string_proc_macro;
 
 fn main() {
     format_string_proc_macro::respan_to_invalid_format_literal!("¡");
-    //~^ ERROR invalid format string: expected `'}'` but string was terminated
     format_args!(r#concat!("¡        {"));
-    //~^ ERROR invalid format string: expected `'}'` but string was terminated
 }
diff --git a/tests/ui/fmt/respanned-literal-issue-106191.stderr b/tests/ui/fmt/respanned-literal-issue-106191.stderr
index 73a3af65a38..16717f42253 100644
--- a/tests/ui/fmt/respanned-literal-issue-106191.stderr
+++ b/tests/ui/fmt/respanned-literal-issue-106191.stderr
@@ -1,19 +1,2 @@
-error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/respanned-literal-issue-106191.rs:6:65
-   |
-LL |     format_string_proc_macro::respan_to_invalid_format_literal!("¡");
-   |                                                                 ^^^ expected `'}'` in format string
-   |
-   = note: if you intended to print `{`, you can escape it using `{{`
-
-error: invalid format string: expected `'}'` but string was terminated
-  --> $DIR/respanned-literal-issue-106191.rs:8:18
-   |
-LL |     format_args!(r#concat!("¡        {"));
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^ expected `'}'` in format string
-   |
-   = note: if you intended to print `{`, you can escape it using `{{`
-   = note: this error originates in the macro `concat` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: aborting due to 2 previous errors
-
+                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  query stack during panic:
+end of query stack