Enforce whitespace ascii character check for doc alias

compiler/rustc_passes/src/check_attr.rs

@@ -303,6 +303,16 @@ impl CheckAttrVisitor<'tcx> {
                                 .emit();
                             return false;
                         }
+                        if doc_alias.starts_with(' ') || doc_alias.ends_with(' ') {
+                            self.tcx
+                                .sess
+                                .struct_span_err(
+                                    meta.span(),
+                                    "`#[doc(alias = \"...\")]` cannot start or end with ' '",
+                                )
+                                .emit();
+                            return false;
+                        }
                         if let Some(err) = match target {
                             Target::Impl => Some("implementation block"),
                             Target::ForeignMod => Some("extern block"),

src/test/rustdoc-ui/check-doc-alias-attr.rs

@@ -12,4 +12,6 @@ pub struct Bar;
 #[doc(alias = "
 ")] //~^ ERROR
 #[doc(alias = "\t")] //~ ERROR
+#[doc(alias = " hello")] //~ ERROR
+#[doc(alias = "hello ")] //~ ERROR
 pub struct Foo;

src/test/rustdoc-ui/check-doc-alias-attr.stderr

@@ -42,5 +42,17 @@ error: '\t' character isn't allowed in `#[doc(alias = "...")]`
 LL | #[doc(alias = "\t")]
    |       ^^^^^^^^^^^^
 
-error: aborting due to 7 previous errors
+error: `#[doc(alias = "...")]` cannot start or end with ' '
+  --> $DIR/check-doc-alias-attr.rs:15:7
+   |
+LL | #[doc(alias = " hello")]
+   |       ^^^^^^^^^^^^^^^^
+
+error: `#[doc(alias = "...")]` cannot start or end with ' '
+  --> $DIR/check-doc-alias-attr.rs:16:7
+   |
+LL | #[doc(alias = "hello ")]
+   |       ^^^^^^^^^^^^^^^^
+
+error: aborting due to 9 previous errors
 

src/test/ui/check-doc-alias-attr.rs

@@ -12,4 +12,6 @@ pub struct Bar;
 #[doc(alias = "
 ")] //~^ ERROR
 #[doc(alias = "\t")] //~ ERROR
+#[doc(alias = " hello")] //~ ERROR
+#[doc(alias = "hello ")] //~ ERROR
 pub struct Foo;

src/test/ui/check-doc-alias-attr.stderr

@@ -42,5 +42,17 @@ error: '\t' character isn't allowed in `#[doc(alias = "...")]`
 LL | #[doc(alias = "\t")]
    |       ^^^^^^^^^^^^
 
-error: aborting due to 7 previous errors
+error: `#[doc(alias = "...")]` cannot start or end with ' '
+  --> $DIR/check-doc-alias-attr.rs:15:7
+   |
+LL | #[doc(alias = " hello")]
+   |       ^^^^^^^^^^^^^^^^
+
+error: `#[doc(alias = "...")]` cannot start or end with ' '
+  --> $DIR/check-doc-alias-attr.rs:16:7
+   |
+LL | #[doc(alias = "hello ")]
+   |       ^^^^^^^^^^^^^^^^
+
+error: aborting due to 9 previous errors