Improve robustness of nested check.

This commit removes the assumption that the start of a use statement
will always be on one line with a single space - which was silly in the
first place.

Author: davidtwco

src/librustc_resolve/error_reporting.rs

@@ -827,28 +827,29 @@ fn find_span_immediately_after_crate_name(
            module_name, use_span);
     let source_map = sess.source_map();
 
-    // Get position of the first `{` character for the use statement.
-    //  ie. `use foo::{a, b::{c, d}};`
-    //                ^
-    let pos_of_use_tree_left_bracket = source_map.span_until_char(use_span, '{').hi();
-    debug!("find_span_immediately_after_crate_name: pos_of_use_tree_left_bracket={:?}",
-           pos_of_use_tree_left_bracket);
-
-    // Calculate the expected difference between the first `{` character and the start of a
-    // use statement.
-    //  ie. `use foo::{..};`
-    //       ^^^^
-    //       |   ^^^
-    //       4   |  ^^
-    //           3  |
-    //              2
-    let expected_difference = BytePos((module_name.as_str().len() + 4 + 2) as u32);
-    debug!("find_span_immediately_after_crate_name: expected_difference={:?}",
-           expected_difference);
-    let actual_difference = pos_of_use_tree_left_bracket - use_span.lo();
-    debug!("find_span_immediately_after_crate_name: actual_difference={:?}",
-           actual_difference);
-
-    (expected_difference == actual_difference,
-     use_span.with_lo(use_span.lo() + expected_difference))
+    // Using `use issue_59764::foo::{baz, makro};` as an example throughout..
+    let mut num_colons = 0;
+    // Find second colon.. `use issue_59764:`
+    let until_second_colon = source_map.span_take_while(use_span, |c| {
+        if *c == ':' { num_colons += 1; }
+        match c {
+            ':' if num_colons == 2 => false,
+            _ => true,
+        }
+    });
+    // Find everything after the second colon.. `foo::{baz, makro};`
+    let from_second_colon = use_span.with_lo(until_second_colon.hi() + BytePos(1));
+
+    let mut found_a_non_whitespace_character = false;
+    // Find the first non-whitespace character in `from_second_colon`.. `f`
+    let after_second_colon = source_map.span_take_while(from_second_colon, |c| {
+        if found_a_non_whitespace_character { return false; }
+        if !c.is_whitespace() { found_a_non_whitespace_character = true; }
+        true
+    });
+
+    // Find the first `{` in from_second_colon.. `foo::{`
+    let next_left_bracket = source_map.span_through_char(from_second_colon, '{');
+
+    (next_left_bracket == after_second_colon, from_second_colon)
 }

src/test/ui/issue-59764.fixed

@@ -109,6 +109,17 @@ mod renamed_multiple_imports {
     //~^ ERROR unresolved import `issue_59764::foo::makro` [E0432]
 }
 
+mod lots_of_whitespace {
+    use issue_59764::{makro as foobar, 
+
+            foobaz,
+
+
+            foo::{baz} //~ ERROR unresolved import `issue_59764::foo::makro` [E0432]
+
+        };
+}
+
 // Simple case..
 
 use issue_59764::makro;

src/test/ui/issue-59764.rs

@@ -109,6 +109,20 @@ mod renamed_multiple_imports {
     //~^ ERROR unresolved import `issue_59764::foo::makro` [E0432]
 }
 
+mod lots_of_whitespace {
+    use
+        issue_59764::{
+
+            foobaz,
+
+
+            foo::{baz,
+
+                makro as foobar} //~ ERROR unresolved import `issue_59764::foo::makro` [E0432]
+
+        };
+}
+
 // Simple case..
 
 use issue_59764::foo::makro;

src/test/ui/issue-59764.stderr

@@ -196,7 +196,24 @@ LL |     use issue_59764::{makro as foobar, foo::{baz}};
    |
 
 error[E0432]: unresolved import `issue_59764::foo::makro`
-  --> $DIR/issue-59764.rs:114:5
+  --> $DIR/issue-59764.rs:121:17
+   |
+LL |                 makro as foobar}
+   |                 ^^^^^^^^^^^^^^^ no `makro` in `foo`
+   |
+   = note: this could be because a macro annotated with `#[macro_export]` will be exported at the root of the crate instead of the module where it is defined
+help: a macro with this name exists at the root of the crate
+   |
+LL |     use issue_59764::{makro as foobar, 
+LL | 
+LL |             foobaz,
+LL | 
+LL | 
+LL |             foo::{baz}
+ ...
+
+error[E0432]: unresolved import `issue_59764::foo::makro`
+  --> $DIR/issue-59764.rs:128:5
    |
 LL | use issue_59764::foo::makro;
    |     ^^^^^^^^^^^^^^^^^^^^^^^ no `makro` in `foo`
@@ -208,20 +225,20 @@ LL | use issue_59764::makro;
    |     ^^^^^^^^^^^^^^^^^^
 
 error: cannot determine resolution for the macro `makro`
-  --> $DIR/issue-59764.rs:117:1
+  --> $DIR/issue-59764.rs:131:1
    |
 LL | makro!(bar);
    | ^^^^^
    |
    = note: import resolution is stuck, try simplifying macro imports
 
 error[E0425]: cannot find function `bar` in this scope
-  --> $DIR/issue-59764.rs:121:5
+  --> $DIR/issue-59764.rs:135:5
    |
 LL |     bar();
    |     ^^^ not found in this scope
 
-error: aborting due to 17 previous errors
+error: aborting due to 18 previous errors
 
 Some errors occurred: E0425, E0432.
 For more information about an error, try `rustc --explain E0425`.