Auto merge of #16275 - davidsemakula:ast-path-segments, r=Veykril

fix: Fix `ast::Path::segments` implementation

calling `ast::Path::segments` on a qualifier currently returns all the segments of the top path instead of just the segments of the qualifier.

The issue can be summarized by the simple failing test below:
```rust
#[test]
fn path_segments() {
    //use ra_ap_syntax::ast;
    let path: ast::Path = ...; // e.g. `ast::Path` for "foo::bar::item".

    let path_segments: Vec<_> = path.segments().collect();
    let qualifier_segments: Vec<_> = path.qualifier().unwrap().segments().collect();
    assert_eq!(path_segments.len(), qualifier_segments.len() + 1); // Fails because `LHS = RHS`.
}
```

This PR:
- Fixes the implementation of `ast::Path::segments`
- Fixes `ast::Path::segments` callers that either implicitly relied on behavior of previous implementation or exhibited other "wrong" behavior directly related to the result of `ast::Path::segments` (all callers have been reviewed, only one required modification)
- Removes unnecessary (and now unused) `ast::Path::segments` alternatives

Author: bors

crates/ide-assists/src/handlers/generate_constant.rs

@@ -50,6 +50,10 @@ pub(crate) fn generate_constant(acc: &mut Assists, ctx: &AssistContext<'_>) -> O
         ty.original().display_source_code(ctx.db(), constant_module.into(), false).ok()?;
     let target = statement.syntax().parent()?.text_range();
     let path = constant_token.syntax().ancestors().find_map(ast::Path::cast)?;
+    if path.parent_path().is_some() {
+        cov_mark::hit!(not_last_path_segment);
+        return None;
+    }
 
     let name_refs = path.segments().map(|s| s.name_ref());
     let mut outer_exists = false;
@@ -250,6 +254,18 @@ fn bar() -> i32 {
 }
 fn bar() -> i32 {
     foo::goo::A_CONSTANT
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_wont_apply_when_not_last_path_segment() {
+        cov_mark::check!(not_last_path_segment);
+        check_assist_not_applicable(
+            generate_constant,
+            r#"mod foo {}
+fn bar() -> i32 {
+    foo::A_CON$0STANT::invalid_segment
 }"#,
         );
     }

crates/ide-db/src/imports/import_assets.rs

@@ -681,11 +681,10 @@ fn path_import_candidate(
         Some(qualifier) => match sema.resolve_path(&qualifier) {
             None => {
                 if qualifier.first_qualifier().map_or(true, |it| sema.resolve_path(&it).is_none()) {
-                    let mut qualifier = qualifier
-                        .segments_of_this_path_only_rev()
+                    let qualifier = qualifier
+                        .segments()
                         .map(|seg| seg.name_ref().map(|name| SmolStr::new(name.text())))
                         .collect::<Option<Vec<_>>>()?;
-                    qualifier.reverse();
                     ImportCandidate::Path(PathImportCandidate { qualifier: Some(qualifier), name })
                 } else {
                     return None;

crates/syntax/src/ast/node_ext.rs

@@ -285,25 +285,23 @@ impl ast::Path {
         self.first_qualifier_or_self().segment()
     }
 
-    // FIXME: Check usages of Self::segments, they might be wrong because of the logic of the bloew function
-    pub fn segments_of_this_path_only_rev(&self) -> impl Iterator<Item = ast::PathSegment> + Clone {
-        self.qualifiers_and_self().filter_map(|it| it.segment())
-    }
-
     pub fn segments(&self) -> impl Iterator<Item = ast::PathSegment> + Clone {
-        successors(self.first_segment(), |p| {
-            p.parent_path().parent_path().and_then(|p| p.segment())
+        let path_range = self.syntax().text_range();
+        successors(self.first_segment(), move |p| {
+            p.parent_path().parent_path().and_then(|p| {
+                if path_range.contains_range(p.syntax().text_range()) {
+                    p.segment()
+                } else {
+                    None
+                }
+            })
         })
     }
 
     pub fn qualifiers(&self) -> impl Iterator<Item = ast::Path> + Clone {
         successors(self.qualifier(), |p| p.qualifier())
     }
 
-    pub fn qualifiers_and_self(&self) -> impl Iterator<Item = ast::Path> + Clone {
-        successors(Some(self.clone()), |p| p.qualifier())
-    }
-
     pub fn top_path(&self) -> ast::Path {
         let mut this = self.clone();
         while let Some(path) = this.parent_path() {