typeck: fix ? suggestion span

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1291,12 +1291,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ty::TraitRef::new(self.tcx, into_def_id, [expr_ty, expected_ty]),
             ))
         {
-            let mut span = expr.span;
-            while expr.span.eq_ctxt(span)
-                && let Some(parent_callsite) = span.parent_callsite()
-            {
-                span = parent_callsite;
-            }
+            let span = expr.span.find_oldest_ancestor_in_same_ctxt();
 
             let mut sugg = if expr.precedence().order() >= PREC_POSTFIX {
                 vec![(span.shrink_to_hi(), ".into()".to_owned())]
@@ -1901,12 +1896,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             None => sugg.to_string(),
         };
 
-        err.span_suggestion_verbose(
-            expr.span.shrink_to_hi(),
-            msg,
-            sugg,
-            Applicability::HasPlaceholders,
-        );
+        let span = expr.span.find_oldest_ancestor_in_same_ctxt();
+        err.span_suggestion_verbose(span.shrink_to_hi(), msg, sugg, Applicability::HasPlaceholders);
         return true;
     }
 

compiler/rustc_span/src/lib.rs

@@ -743,6 +743,45 @@ impl Span {
         Some(self)
     }
 
+    /// Recursively walk down the expansion ancestors to find the oldest ancestor span with the same
+    /// [`SyntaxContext`] the initial span.
+    ///
+    /// This method is suitable for peeling through *local* macro expansions to find the "innermost"
+    /// span that is still local and shares the same [`SyntaxContext`]. For example, given
+    ///
+    /// ```ignore (illustrative example, contains type error)
+    ///  macro_rules! outer {
+    ///      ($x: expr) => {
+    ///          inner!($x)
+    ///      }
+    ///  }
+    ///
+    ///  macro_rules! inner {
+    ///      ($x: expr) => {
+    ///          format!("error: {}", $x)
+    ///          //~^ ERROR mismatched types
+    ///      }
+    ///  }
+    ///
+    ///  fn bar(x: &str) -> Result<(), Box<dyn std::error::Error>> {
+    ///      Err(outer!(x))
+    ///  }
+    /// ```
+    ///
+    /// if provided the initial span of `outer!(x)` inside `bar`, this method will recurse
+    /// the parent callsites until we reach `format!("error: {}", $x)`, at which point it is the
+    /// oldest ancestor span that is both still local and shares the same [`SyntaxContext`] as the
+    /// initial span.
+    pub fn find_oldest_ancestor_in_same_ctxt(self) -> Span {
+        let mut cur = self;
+        while cur.eq_ctxt(self)
+            && let Some(parent_callsite) = cur.parent_callsite()
+        {
+            cur = parent_callsite;
+        }
+        cur
+    }
+
     /// Edition of the crate from which this span came.
     pub fn edition(self) -> edition::Edition {
         self.ctxt().edition()

tests/ui/typeck/issue-112007-leaked-writeln-macro-internals.rs

@@ -1,8 +1,16 @@
-//@ run-rustfix
-#![allow(dead_code)]
+// Check that we don't leak stdlib implementation details through suggestions.
+// Also check that the suggestion provided tries as hard as it can to see through local macros.
+//
+// FIXME(jieyouxu): this test is NOT run-rustfix because this test contains conflicting
+// MaybeIncorrect suggestions:
+//
+// 1. `return ... ;`
+// 2. `?`
+//
+// when the suggestions are applied to the same file, it becomes uncompilable.
 
 // https://github.com/rust-lang/rust/issues/112007
-fn bug_report<W: std::fmt::Write>(w: &mut W) -> std::fmt::Result {
+pub fn bug_report<W: std::fmt::Write>(w: &mut W) -> std::fmt::Result {
     if true {
         writeln!(w, "`;?` here ->")?;
     } else {
@@ -25,7 +33,7 @@ macro_rules! bar {
     }
 }
 
-fn foo<W: std::fmt::Write>(w: &mut W) -> std::fmt::Result {
+pub fn foo<W: std::fmt::Write>(w: &mut W) -> std::fmt::Result {
     if true {
         writeln!(w, "`;?` here ->")?;
     } else {
@@ -34,4 +42,4 @@ fn foo<W: std::fmt::Write>(w: &mut W) -> std::fmt::Result {
     Ok(())
 }
 
-fn main() {}
+pub fn main() {}

tests/ui/typeck/issue-112007-leaked-writeln-macro-internals.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/issue-112007-leaked-writeln-macro-internals.rs:9:9
+  --> $DIR/issue-112007-leaked-writeln-macro-internals.rs:17:9
    |
 LL | /     if true {
 LL | |         writeln!(w, "`;?` here ->")?;
@@ -21,9 +21,13 @@ help: you might have meant to return this value
    |
 LL |         return writeln!(w, "but not here");
    |         ++++++                            +
+help: use the `?` operator to extract the `Result<(), std::fmt::Error>` value, propagating a `Result::Err` value to the caller
+   |
+LL |         writeln!(w, "but not here")?
+   |                                    +
 
 error[E0308]: mismatched types
-  --> $DIR/issue-112007-leaked-writeln-macro-internals.rs:32:9
+  --> $DIR/issue-112007-leaked-writeln-macro-internals.rs:40:9
    |
 LL | /     if true {
 LL | |         writeln!(w, "`;?` here ->")?;
@@ -44,6 +48,10 @@ help: you might have meant to return this value
    |
 LL |         return baz!(w);
    |         ++++++        +
+help: use the `?` operator to extract the `Result<(), std::fmt::Error>` value, propagating a `Result::Err` value to the caller
+   |
+LL |         writeln!($w, "but not here")?
+   |                                     +
 
 error: aborting due to 2 previous errors
 

tests/ui/typeck/question-mark-operator-suggestion-span.rs

@@ -0,0 +1,22 @@
+// Check that we don't construct a span for `?` suggestions that point into non-local macros
+// like into the stdlib where the user has no control over.
+//
+// FIXME(jieyouxu): this test is currently NOT run-rustfix because there are conflicting
+// MaybeIncorrect suggestions:
+//
+// 1. adding `return ... ;`, and
+// 2. adding `?`.
+//
+// When rustfix puts those together, the fixed file now contains uncompilable code.
+
+#![crate_type = "lib"]
+
+pub fn bug_report<W: std::fmt::Write>(w: &mut W) -> std::fmt::Result {
+    if true {
+        writeln!(w, "`;?` here ->")?;
+    } else {
+        writeln!(w, "but not here")
+        //~^ ERROR mismatched types
+    }
+    Ok(())
+}

tests/ui/typeck/question-mark-operator-suggestion-span.stderr

@@ -0,0 +1,31 @@
+error[E0308]: mismatched types
+  --> $DIR/question-mark-operator-suggestion-span.rs:18:9
+   |
+LL | /     if true {
+LL | |         writeln!(w, "`;?` here ->")?;
+LL | |     } else {
+LL | |         writeln!(w, "but not here")
+   | |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `()`, found `Result<(), Error>`
+LL | |
+LL | |     }
+   | |_____- expected this to be `()`
+   |
+   = note: expected unit type `()`
+                   found enum `Result<(), std::fmt::Error>`
+   = note: this error originates in the macro `writeln` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider using a semicolon here
+   |
+LL |     };
+   |      +
+help: you might have meant to return this value
+   |
+LL |         return writeln!(w, "but not here");
+   |         ++++++                            +
+help: use the `?` operator to extract the `Result<(), std::fmt::Error>` value, propagating a `Result::Err` value to the caller
+   |
+LL |         writeln!(w, "but not here")?
+   |                                    +
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.