Merge #8873

8873: Implement import-granularity guessing  r=matklad a=Veykril

This renames our `MergeBehavior` to `ImportGranularity` as rustfmt has it as the purpose of them are basically the same. `ImportGranularity::Preserve` currently has no specific purpose for us as we don't have an organize imports assist yet, so it currently acts the same as `ImportGranularity::Item`.

We now try to guess the import style on a per file basis and fall back to the user granularity setting if the file has no specific style yet or where it is ambiguous. This can be turned off by setting `import.enforceGranularity` to `true`.

Closes https://github.com/rust-analyzer/rust-analyzer/issues/8870

Co-authored-by: Lukas Tobias Wirth <[email protected]>

1 files changed, 101 insertions, 4 deletions

diff --git a/crates/ide_db/src/helpers/insert_use.rs b/crates/ide_db/src/helpers/insert_use.rs
index 55cdc4da3..aa61c5bcb 100644
--- a/crates/ide_db/src/helpers/insert_use.rs
+++ b/crates/ide_db/src/helpers/insert_use.rs
@@ -4,20 +4,36 @@ use std::cmp::Ordering;
 use hir::Semantics;
 use syntax::{
     algo,
-    ast::{self, make, AstNode, PathSegmentKind},
+    ast::{self, make, AstNode, AttrsOwner, ModuleItemOwner, PathSegmentKind, VisibilityOwner},
     ted, AstToken, Direction, NodeOrToken, SyntaxNode, SyntaxToken,
 };
 
 use crate::{
-    helpers::merge_imports::{try_merge_imports, use_tree_path_cmp, MergeBehavior},
+    helpers::merge_imports::{
+        common_prefix, eq_attrs, eq_visibility, try_merge_imports, use_tree_path_cmp, MergeBehavior,
+    },
     RootDatabase,
 };
 
 pub use hir::PrefixKind;
 
+/// How imports should be grouped into use statements.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ImportGranularity {
+    /// Do not change the granularity of any imports and preserve the original structure written by the developer.
+    Preserve,
+    /// Merge imports from the same crate into a single use statement.
+    Crate,
+    /// Merge imports from the same module into a single use statement.
+    Module,
+    /// Flatten imports so that each has its own use statement.
+    Item,
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct InsertUseConfig {
-    pub merge: Option<MergeBehavior>,
+    pub granularity: ImportGranularity,
+    pub enforce_granularity: bool,
     pub prefix_kind: PrefixKind,
     pub group: bool,
 }
@@ -65,15 +81,96 @@ impl ImportScope {
             ImportScope::Module(item_list) => ImportScope::Module(item_list.clone_for_update()),
         }
     }
+
+    fn guess_granularity_from_scope(&self) -> ImportGranularityGuess {
+        // The idea is simple, just check each import as well as the import and its precedent together for
+        // whether they fulfill a granularity criteria.
+        let use_stmt = |item| match item {
+            ast::Item::Use(use_) => {
+                let use_tree = use_.use_tree()?;
+                Some((use_tree, use_.visibility(), use_.attrs()))
+            }
+            _ => None,
+        };
+        let mut use_stmts = match self {
+            ImportScope::File(f) => f.items(),
+            ImportScope::Module(m) => m.items(),
+        }
+        .filter_map(use_stmt);
+        let mut res = ImportGranularityGuess::Unknown;
+        let (mut prev, mut prev_vis, mut prev_attrs) = match use_stmts.next() {
+            Some(it) => it,
+            None => return res,
+        };
+        loop {
+            if let Some(use_tree_list) = prev.use_tree_list() {
+                if use_tree_list.use_trees().any(|tree| tree.use_tree_list().is_some()) {
+                    // Nested tree lists can only occur in crate style, or with no proper style being enforced in the file.
+                    break ImportGranularityGuess::Crate;
+                } else {
+                    // Could still be crate-style so continue looking.
+                    res = ImportGranularityGuess::CrateOrModule;
+                }
+            }
+
+            let (curr, curr_vis, curr_attrs) = match use_stmts.next() {
+                Some(it) => it,
+                None => break res,
+            };
+            if eq_visibility(prev_vis, curr_vis.clone()) && eq_attrs(prev_attrs, curr_attrs.clone())
+            {
+                if let Some((prev_path, curr_path)) = prev.path().zip(curr.path()) {
+                    if let Some(_) = common_prefix(&prev_path, &curr_path) {
+                        if prev.use_tree_list().is_none() && curr.use_tree_list().is_none() {
+                            // Same prefix but no use tree lists so this has to be of item style.
+                            break ImportGranularityGuess::Item; // this overwrites CrateOrModule, technically the file doesn't adhere to anything here.
+                        } else {
+                            // Same prefix with item tree lists, has to be module style as it
+                            // can't be crate style since the trees wouldn't share a prefix then.
+                            break ImportGranularityGuess::Module;
+                        }
+                    }
+                }
+            }
+            prev = curr;
+            prev_vis = curr_vis;
+            prev_attrs = curr_attrs;
+        }
+    }
+}
+
+#[derive(PartialEq, PartialOrd, Debug, Clone, Copy)]
+enum ImportGranularityGuess {
+    Unknown,
+    Item,
+    Module,
+    Crate,
+    CrateOrModule,
 }
 
 /// Insert an import path into the given file/node. A `merge` value of none indicates that no import merging is allowed to occur.
 pub fn insert_use<'a>(scope: &ImportScope, path: ast::Path, cfg: InsertUseConfig) {
     let _p = profile::span("insert_use");
+    let mut mb = match cfg.granularity {
+        ImportGranularity::Crate => Some(MergeBehavior::Crate),
+        ImportGranularity::Module => Some(MergeBehavior::Module),
+        ImportGranularity::Item | ImportGranularity::Preserve => None,
+    };
+    if !cfg.enforce_granularity {
+        let file_granularity = scope.guess_granularity_from_scope();
+        mb = match file_granularity {
+            ImportGranularityGuess::Unknown => mb,
+            ImportGranularityGuess::Item => None,
+            ImportGranularityGuess::Module => Some(MergeBehavior::Module),
+            ImportGranularityGuess::Crate => Some(MergeBehavior::Crate),
+            ImportGranularityGuess::CrateOrModule => mb.or(Some(MergeBehavior::Crate)),
+        };
+    }
+
     let use_item =
         make::use_(None, make::use_tree(path.clone(), None, None, false)).clone_for_update();
     // merge into existing imports if possible
-    if let Some(mb) = cfg.merge {
+    if let Some(mb) = mb {
         for existing_use in scope.as_syntax_node().children().filter_map(ast::Use::cast) {
             if let Some(merged) = try_merge_imports(&existing_use, &use_item, mb) {
                 ted::replace(existing_use.syntax(), merged.syntax());