Make struct_field_names lint on private fields of public structs.

Currently, If a struct is `pub` and its field is private, and
`avoid-breaking-exported-api = true` (default), then `struct_field_names`
will not lint the field, even though changing the field’s name is not a
breaking change. This is because the breaking-exported-api condition was
checking the visibility of the struct, not its fields (perhaps because
the same code was used for enums). With this change, Clippy will check
 the field’s effective visibility only.

Note: This change is large because some functions were moved into an
`impl` to be able to access more configuration. Consider viewing the
diff with whitespace ignored.

Author: kpreid

clippy_lints/src/item_name_repetitions.rs

@@ -196,80 +196,100 @@ fn have_no_extra_prefix(prefixes: &[&str]) -> bool {
     prefixes.iter().all(|p| p == &"" || p == &"_")
 }
 
-fn check_fields(cx: &LateContext<'_>, threshold: u64, item: &Item<'_>, fields: &[FieldDef<'_>]) {
-    if (fields.len() as u64) < threshold {
-        return;
-    }
-
-    check_struct_name_repetition(cx, item, fields);
+impl ItemNameRepetitions {
+    /// Lint the names of struct fields against the name of the struct.
+    fn check_fields(&self, cx: &LateContext<'_>, item: &Item<'_>, fields: &[FieldDef<'_>]) {
+        if (fields.len() as u64) < self.struct_threshold {
+            return;
+        }
 
-    // if the SyntaxContext of the identifiers of the fields and struct differ dont lint them.
-    // this prevents linting in macros in which the location of the field identifier names differ
-    if !fields.iter().all(|field| item.ident.span.eq_ctxt(field.ident.span)) {
-        return;
+        self.check_struct_name_repetition(cx, item, fields);
+        self.check_common_affix(cx, item, fields);
     }
 
-    let mut pre: Vec<&str> = match fields.first() {
-        Some(first_field) => first_field.ident.name.as_str().split('_').collect(),
-        None => return,
-    };
-    let mut post = pre.clone();
-    post.reverse();
-    for field in fields {
-        let field_split: Vec<&str> = field.ident.name.as_str().split('_').collect();
-        if field_split.len() == 1 {
+    fn check_common_affix(&self, cx: &LateContext<'_>, item: &Item<'_>, fields: &[FieldDef<'_>]) {
+        // if the SyntaxContext of the identifiers of the fields and struct differ dont lint them.
+        // this prevents linting in macros in which the location of the field identifier names differ
+        if !fields.iter().all(|field| item.ident.span.eq_ctxt(field.ident.span)) {
             return;
         }
 
-        pre = pre
-            .into_iter()
-            .zip(field_split.iter())
-            .take_while(|(a, b)| &a == b)
-            .map(|e| e.0)
-            .collect();
-        post = post
-            .into_iter()
-            .zip(field_split.iter().rev())
-            .take_while(|(a, b)| &a == b)
-            .map(|e| e.0)
-            .collect();
-    }
-    let prefix = pre.join("_");
-    post.reverse();
-    let postfix = match post.last() {
-        Some(&"") => post.join("_") + "_",
-        Some(_) | None => post.join("_"),
-    };
-    if fields.len() > 1 {
-        let (what, value) = match (
-            prefix.is_empty() || prefix.chars().all(|c| c == '_'),
-            postfix.is_empty(),
-        ) {
-            (true, true) => return,
-            (false, _) => ("pre", prefix),
-            (true, false) => ("post", postfix),
-        };
-        if fields.iter().all(|field| is_bool(field.ty)) {
-            // If all fields are booleans, we don't want to emit this lint.
+        if self.avoid_breaking_exported_api
+            && fields
+                .iter()
+                .any(|field| cx.effective_visibilities.is_exported(field.def_id))
+        {
             return;
         }
-        span_lint_and_help(
-            cx,
-            STRUCT_FIELD_NAMES,
-            item.span,
-            format!("all fields have the same {what}fix: `{value}`"),
-            None,
-            format!("remove the {what}fixes"),
-        );
+
+        let mut pre: Vec<&str> = match fields.first() {
+            Some(first_field) => first_field.ident.name.as_str().split('_').collect(),
+            None => return,
+        };
+        let mut post = pre.clone();
+        post.reverse();
+        for field in fields {
+            let field_split: Vec<&str> = field.ident.name.as_str().split('_').collect();
+            if field_split.len() == 1 {
+                return;
+            }
+
+            pre = pre
+                .into_iter()
+                .zip(field_split.iter())
+                .take_while(|(a, b)| &a == b)
+                .map(|e| e.0)
+                .collect();
+            post = post
+                .into_iter()
+                .zip(field_split.iter().rev())
+                .take_while(|(a, b)| &a == b)
+                .map(|e| e.0)
+                .collect();
+        }
+        let prefix = pre.join("_");
+        post.reverse();
+        let postfix = match post.last() {
+            Some(&"") => post.join("_") + "_",
+            Some(_) | None => post.join("_"),
+        };
+        if fields.len() > 1 {
+            let (what, value) = match (
+                prefix.is_empty() || prefix.chars().all(|c| c == '_'),
+                postfix.is_empty(),
+            ) {
+                (true, true) => return,
+                (false, _) => ("pre", prefix),
+                (true, false) => ("post", postfix),
+            };
+            if fields.iter().all(|field| is_bool(field.ty)) {
+                // If all fields are booleans, we don't want to emit this lint.
+                return;
+            }
+            span_lint_and_help(
+                cx,
+                STRUCT_FIELD_NAMES,
+                item.span,
+                format!("all fields have the same {what}fix: `{value}`"),
+                None,
+                format!("remove the {what}fixes"),
+            );
+        }
     }
-}
 
-fn check_struct_name_repetition(cx: &LateContext<'_>, item: &Item<'_>, fields: &[FieldDef<'_>]) {
-    let snake_name = to_snake_case(item.ident.name.as_str());
-    let item_name_words: Vec<&str> = snake_name.split('_').collect();
-    for field in fields {
-        if field.ident.span.eq_ctxt(item.ident.span) {
-            //consider linting only if the field identifier has the same SyntaxContext as the item(struct)
+    fn check_struct_name_repetition(&self, cx: &LateContext<'_>, item: &Item<'_>, fields: &[FieldDef<'_>]) {
+        let snake_name = to_snake_case(item.ident.name.as_str());
+        let item_name_words: Vec<&str> = snake_name.split('_').collect();
+        for field in fields {
+            if self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(field.def_id) {
+                continue;
+            }
+
+            if !field.ident.span.eq_ctxt(item.ident.span) {
+                // consider linting only if the field identifier has the same SyntaxContext as the item(struct)
+                continue;
+            }
+
             let field_words: Vec<&str> = field.ident.name.as_str().split('_').collect();
             if field_words.len() >= item_name_words.len() {
                 // if the field name is shorter than the struct name it cannot contain it
@@ -458,17 +478,23 @@ impl LateLintPass<'_> for ItemNameRepetitions {
                 }
             }
         }
-        if !(self.avoid_breaking_exported_api && cx.effective_visibilities.is_exported(item.owner_id.def_id))
-            && span_is_local(item.span)
-        {
+
+        if span_is_local(item.span) {
             match item.kind {
-                ItemKind::Enum(def, _) => check_variant(cx, self.enum_threshold, &def, item_name, item.span),
+                ItemKind::Enum(def, _) => {
+                    if !(self.avoid_breaking_exported_api
+                        && cx.effective_visibilities.is_exported(item.owner_id.def_id))
+                    {
+                        check_variant(cx, self.enum_threshold, &def, item_name, item.span);
+                    }
+                },
                 ItemKind::Struct(VariantData::Struct { fields, .. }, _) => {
-                    check_fields(cx, self.struct_threshold, item, fields);
+                    self.check_fields(cx, item, fields);
                 },
                 _ => (),
             }
         }
+
         self.modules.push((item.ident.name, item_camel, item.owner_id));
     }
 }

tests/ui/struct_fields.rs

@@ -344,4 +344,31 @@ struct Use {
     //~^ struct_field_names
 }
 
+// should lint on private fields of public structs (renaming them is not breaking-exported-api)
+pub struct PubStructFieldNamedAfterStruct {
+    pub_struct_field_named_after_struct: bool,
+    //~^ ERROR: field name starts with the struct's name
+    other1: bool,
+    other2: bool,
+}
+pub struct PubStructFieldPrefix {
+    //~^ ERROR: all fields have the same prefix: `field`
+    field_foo: u8,
+    field_bar: u8,
+    field_baz: u8,
+}
+// ...but should not lint on structs with public fields.
+pub struct PubStructPubAndPrivateFields {
+    /// One could argue that this field should be linted, but currently, any public field stops all
+    /// checking.
+    pub_struct_pub_and_private_fields_1: bool,
+    pub pub_struct_pub_and_private_fields_2: bool,
+}
+// nor on common prefixes if one of the involved fields is public
+pub struct PubStructPubAndPrivateFieldPrefix {
+    pub field_foo: u8,
+    field_bar: u8,
+    field_baz: u8,
+}
+
 fn main() {}

tests/ui/struct_fields.stderr

@@ -281,5 +281,24 @@ error: field name starts with the struct's name
 LL |     use_baz: bool,
    |     ^^^^^^^^^^^^^
 
-error: aborting due to 24 previous errors
+error: field name starts with the struct's name
+  --> tests/ui/struct_fields.rs:349:5
+   |
+LL |     pub_struct_field_named_after_struct: bool,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: all fields have the same prefix: `field`
+  --> tests/ui/struct_fields.rs:354:1
+   |
+LL | / pub struct PubStructFieldPrefix {
+LL | |
+LL | |     field_foo: u8,
+LL | |     field_bar: u8,
+LL | |     field_baz: u8,
+LL | | }
+   | |_^
+   |
+   = help: remove the prefixes
+
+error: aborting due to 26 previous errors