Fix enum_glob_use false positives

Closes #2397.

This checks the def of the `ItemUse` path instead of checking the
capitalization of the path segements. It was noted that this def would
sometimes be `Def::Mod` instead of `Def::Enum` but it seems correct now.

clippy_lints/src/enum_glob_use.rs

@@ -1,6 +1,7 @@
 //! lint on `use`ing all variants of an enum
 
 use rustc::hir::*;
+use rustc::hir::def::Def;
 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
 use syntax::ast::NodeId;
 use syntax::codemap::Span;
@@ -12,8 +13,7 @@ use utils::span_lint;
 /// an enumeration variant, rather than importing variants.
 ///
 /// **Known problems:** Old-style enumerations that prefix the variants are
-/// still around. May cause problems with modules that are not snake_case (see
-/// [#2397](https://github.com/rust-lang-nursery/rust-clippy/issues/2397))
+/// still around.
 ///
 /// **Example:**
 /// ```rust
@@ -48,16 +48,13 @@ impl EnumGlobUse {
             return; // re-exports are fine
         }
         if let ItemUse(ref path, UseKind::Glob) = item.node {
-            // FIXME: ask jseyfried why the qpath.def for `use std::cmp::Ordering::*;`
-            // extracted through `ItemUse(ref qpath, UseKind::Glob)` is a `Mod` and not an
-            // `Enum`
-            // if let Def::Enum(_) = path.def {
-            if path.segments
-                .last()
-                .and_then(|seg| seg.name.as_str().chars().next())
-                .map_or(false, char::is_uppercase)
-            {
-                span_lint(cx, ENUM_GLOB_USE, item.span, "don't use glob imports for enum variants");
+            if let Def::Enum(_) = path.def {
+                span_lint(
+                    cx,
+                    ENUM_GLOB_USE,
+                    item.span,
+                    "don't use glob imports for enum variants",
+                );
             }
         }
     }

tests/ui/enum_glob_use.rs

@@ -23,4 +23,10 @@ mod tests {
     use super::*;
 }
 
+#[allow(non_snake_case)]
+mod CamelCaseName {
+}
+
+use CamelCaseName::*;
+
 fn main() {}