Update substring match for substitutions

compiler/rustc_errors/src/lib.rs

@@ -306,6 +306,19 @@ impl TrimmedSubstitutionPart {
 /// `BB` is. Return the length of the prefix, the "trimmed" suggestion, and the length
 /// of the suffix.
 fn as_substr<'a>(original: &'a str, suggestion: &'a str) -> Option<(usize, &'a str, usize)> {
+    // Case for import paths where the suggestion shares a prefix with the original.
+    // Without this, suggesting `std::sync` for `sync` would incorrectly highlight `td::s`
+    // instead of `std::` because of the common 's' prefix. See #148070.
+    if suggestion.contains("::")
+        && suggestion.ends_with(original)
+        && suggestion.len() > original.len()
+        && let prefix = &suggestion[..suggestion.len() - original.len()]
+        && prefix.ends_with("::")
+        && suggestion.chars().next() == original.chars().next()
+    {
+        return Some((0, prefix, original.len()));
+    }
+
     let common_prefix = original
         .chars()
         .zip(suggestion.chars())

tests/ui/imports/same-prefix-unresolved-import-148070.rs

@@ -0,0 +1,5 @@
+// https://github.com/rust-lang/rust/issues/148070
+#![no_main]
+use stat; //~ ERROR unresolved import `stat`
+use str; //~ ERROR unresolved import `str`
+use sync; //~ ERROR unresolved import `sync`

tests/ui/imports/same-prefix-unresolved-import-148070.stderr

@@ -0,0 +1,43 @@
+error[E0432]: unresolved import `stat`
+  --> $DIR/same-prefix-unresolved-import-148070.rs:3:5
+   |
+LL | use stat;
+   |     ^^^^ no `stat` in the root
+   |
+help: consider importing this struct instead
+   |
+LL | use std::os::linux::raw::stat;
+   |     +++++++++++++++++++++
+
+error[E0432]: unresolved import `str`
+  --> $DIR/same-prefix-unresolved-import-148070.rs:4:5
+   |
+LL | use str;
+   |     ^^^ no `str` in the root
+   |
+help: a similar name exists in the module
+   |
+LL - use str;
+LL + use std;
+   |
+help: consider importing one of these items instead
+   |
+LL | use std::primitive::str;
+   |     ++++++++++++++++
+LL | use std::str;
+   |     +++++
+
+error[E0432]: unresolved import `sync`
+  --> $DIR/same-prefix-unresolved-import-148070.rs:5:5
+   |
+LL | use sync;
+   |     ^^^^ no `sync` in the root
+   |
+help: consider importing this module instead
+   |
+LL | use std::sync;
+   |     +++++
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0432`.

tests/ui/test-attrs/inaccessible-test-modules.stderr

@@ -13,7 +13,7 @@ LL | use test as y;
 help: consider importing this module instead
    |
 LL | use test::test as y;
-   |         ++++++
+   |     ++++++
 
 error: aborting due to 2 previous errors