1 files changed, 199 insertions, 171 deletions

diff --git a/crates/ide_completion/src/context.rs b/crates/ide_completion/src/context.rs
index 1ec59ff80..8d6440cb2 100644
--- a/crates/ide_completion/src/context.rs
+++ b/crates/ide_completion/src/context.rs
@@ -1,29 +1,34 @@
 //! See `CompletionContext` structure.
 
 use hir::{Local, ScopeDef, Semantics, SemanticsScope, Type};
-use ide_db::base_db::{FilePosition, SourceDatabase};
-use ide_db::{call_info::ActiveParameter, RootDatabase};
+use ide_db::{
+    base_db::{FilePosition, SourceDatabase},
+    call_info::ActiveParameter,
+    RootDatabase,
+};
 use syntax::{
     algo::find_node_at_offset,
     ast::{self, NameOrNameRef, NameOwner},
     match_ast, AstNode, NodeOrToken,
-    SyntaxKind::*,
-    SyntaxNode, SyntaxToken, TextRange, TextSize,
+    SyntaxKind::{self, *},
+    SyntaxNode, SyntaxToken, TextRange, TextSize, T,
 };
-
 use text_edit::Indel;
 
 use crate::{
     patterns::{
-        fn_is_prev, for_is_prev2, has_bind_pat_parent, has_block_expr_parent,
-        has_field_list_parent, has_impl_as_prev_sibling, has_impl_parent,
-        has_item_list_or_source_file_parent, has_ref_parent, has_trait_as_prev_sibling,
-        has_trait_parent, if_is_prev, inside_impl_trait_block, is_in_loop_body, is_match_arm,
-        unsafe_is_prev,
+        determine_location, determine_prev_sibling, for_is_prev2, inside_impl_trait_block,
+        is_in_loop_body, is_match_arm, previous_token, ImmediateLocation, ImmediatePrevSibling,
     },
     CompletionConfig,
 };
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub(crate) enum PatternRefutability {
+    Refutable,
+    Irrefutable,
+}
+
 /// `CompletionContext` is created early during completion to figure out, where
 /// exactly is the cursor, syntax-wise.
 #[derive(Debug)]
@@ -41,28 +46,38 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) expected_name: Option<NameOrNameRef>,
     pub(super) expected_type: Option<Type>,
     pub(super) name_ref_syntax: Option<ast::NameRef>,
-    pub(super) lifetime_syntax: Option<ast::Lifetime>,
-    pub(super) lifetime_param_syntax: Option<ast::LifetimeParam>,
-    pub(super) function_syntax: Option<ast::Fn>,
+
     pub(super) use_item_syntax: Option<ast::Use>,
+
+    /// The parent function of the cursor position if it exists.
+    pub(super) function_def: Option<ast::Fn>,
+    /// The parent impl of the cursor position if it exists.
+    pub(super) impl_def: Option<ast::Impl>,
+
+    /// RecordExpr the token is a field of
     pub(super) record_lit_syntax: Option<ast::RecordExpr>,
+    /// RecordPat the token is a field of
     pub(super) record_pat_syntax: Option<ast::RecordPat>,
-    pub(super) record_field_syntax: Option<ast::RecordExprField>,
-    pub(super) impl_def: Option<ast::Impl>,
+
+    // potentially set if we are completing a lifetime
+    pub(super) lifetime_syntax: Option<ast::Lifetime>,
+    pub(super) lifetime_param_syntax: Option<ast::LifetimeParam>,
     pub(super) lifetime_allowed: bool,
+    pub(super) is_label_ref: bool,
+
+    // potentially set if we are completing a name
+    pub(super) is_pat_or_const: Option<PatternRefutability>,
+    pub(super) is_param: bool,
+
+    pub(super) completion_location: Option<ImmediateLocation>,
+    pub(super) prev_sibling: Option<ImmediatePrevSibling>,
+
     /// FIXME: `ActiveParameter` is string-based, which is very very wrong
     pub(super) active_parameter: Option<ActiveParameter>,
-    pub(super) is_param: bool,
-    pub(super) is_label_ref: bool,
-    /// If a name-binding or reference to a const in a pattern.
-    /// Irrefutable patterns (like let) are excluded.
-    pub(super) is_pat_binding_or_const: bool,
-    pub(super) is_irrefutable_pat_binding: bool,
     /// A single-indent path, like `foo`. `::foo` should not be considered a trivial path.
     pub(super) is_trivial_path: bool,
     /// If not a trivial path, the prefix (qualifier).
     pub(super) path_qual: Option<ast::Path>,
-    pub(super) after_if: bool,
     /// `true` if we are a statement or a last expr in the block.
     pub(super) can_be_stmt: bool,
     /// `true` if we expect an expression at the cursor position.
@@ -82,24 +97,15 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) has_type_args: bool,
     pub(super) attribute_under_caret: Option<ast::Attr>,
     pub(super) mod_declaration_under_caret: Option<ast::Module>,
-    pub(super) unsafe_is_prev: bool,
-    pub(super) if_is_prev: bool,
-    pub(super) block_expr_parent: bool,
-    pub(super) bind_pat_parent: bool,
-    pub(super) ref_pat_parent: bool,
+    pub(super) locals: Vec<(String, Local)>,
+
+    // keyword patterns
+    pub(super) previous_token: Option<SyntaxToken>,
     pub(super) in_loop_body: bool,
-    pub(super) has_trait_parent: bool,
-    pub(super) has_impl_parent: bool,
-    pub(super) inside_impl_trait_block: bool,
-    pub(super) has_field_list_parent: bool,
-    pub(super) trait_as_prev_sibling: bool,
-    pub(super) impl_as_prev_sibling: bool,
     pub(super) is_match_arm: bool,
-    pub(super) has_item_list_or_source_file_parent: bool,
-    pub(super) for_is_prev2: bool,
-    pub(super) fn_is_prev: bool,
     pub(super) incomplete_let: bool,
-    pub(super) locals: Vec<(String, Local)>,
+
+    no_completion_required: bool,
 }
 
 impl<'a> CompletionContext<'a> {
@@ -149,20 +155,17 @@ impl<'a> CompletionContext<'a> {
             name_ref_syntax: None,
             lifetime_syntax: None,
             lifetime_param_syntax: None,
-            function_syntax: None,
+            function_def: None,
             use_item_syntax: None,
             record_lit_syntax: None,
             record_pat_syntax: None,
-            record_field_syntax: None,
             impl_def: None,
             active_parameter: ActiveParameter::at(db, position),
             is_label_ref: false,
             is_param: false,
-            is_pat_binding_or_const: false,
-            is_irrefutable_pat_binding: false,
+            is_pat_or_const: None,
             is_trivial_path: false,
             path_qual: None,
-            after_if: false,
             can_be_stmt: false,
             is_expr: false,
             is_new_item: false,
@@ -175,67 +178,57 @@ impl<'a> CompletionContext<'a> {
             has_type_args: false,
             attribute_under_caret: None,
             mod_declaration_under_caret: None,
-            unsafe_is_prev: false,
-            if_is_prev: false,
-            block_expr_parent: false,
-            bind_pat_parent: false,
-            ref_pat_parent: false,
+            previous_token: None,
             in_loop_body: false,
-            has_trait_parent: false,
-            has_impl_parent: false,
-            inside_impl_trait_block: false,
-            has_field_list_parent: false,
-            trait_as_prev_sibling: false,
-            impl_as_prev_sibling: false,
+            completion_location: None,
+            prev_sibling: None,
             is_match_arm: false,
-            has_item_list_or_source_file_parent: false,
-            for_is_prev2: false,
-            fn_is_prev: false,
+            no_completion_required: false,
             incomplete_let: false,
             locals,
         };
 
         let mut original_file = original_file.syntax().clone();
-        let mut hypothetical_file = file_with_fake_ident.syntax().clone();
+        let mut speculative_file = file_with_fake_ident.syntax().clone();
         let mut offset = position.offset;
         let mut fake_ident_token = fake_ident_token;
 
         // Are we inside a macro call?
         while let (Some(actual_macro_call), Some(macro_call_with_fake_ident)) = (
             find_node_at_offset::<ast::MacroCall>(&original_file, offset),
-            find_node_at_offset::<ast::MacroCall>(&hypothetical_file, offset),
+            find_node_at_offset::<ast::MacroCall>(&speculative_file, offset),
         ) {
             if actual_macro_call.path().as_ref().map(|s| s.syntax().text())
                 != macro_call_with_fake_ident.path().as_ref().map(|s| s.syntax().text())
             {
                 break;
             }
-            let hypothetical_args = match macro_call_with_fake_ident.token_tree() {
+            let speculative_args = match macro_call_with_fake_ident.token_tree() {
                 Some(tt) => tt,
                 None => break,
             };
-            if let (Some(actual_expansion), Some(hypothetical_expansion)) = (
+            if let (Some(actual_expansion), Some(speculative_expansion)) = (
                 ctx.sema.expand(&actual_macro_call),
                 ctx.sema.speculative_expand(
                     &actual_macro_call,
-                    &hypothetical_args,
+                    &speculative_args,
                     fake_ident_token,
                 ),
             ) {
-                let new_offset = hypothetical_expansion.1.text_range().start();
+                let new_offset = speculative_expansion.1.text_range().start();
                 if new_offset > actual_expansion.text_range().end() {
                     break;
                 }
                 original_file = actual_expansion;
-                hypothetical_file = hypothetical_expansion.0;
-                fake_ident_token = hypothetical_expansion.1;
+                speculative_file = speculative_expansion.0;
+                fake_ident_token = speculative_expansion.1;
                 offset = new_offset;
             } else {
                 break;
             }
         }
-        ctx.fill_keyword_patterns(&hypothetical_file, offset);
-        ctx.fill(&original_file, hypothetical_file, offset);
+        ctx.fill_keyword_patterns(&speculative_file, offset);
+        ctx.fill(&original_file, speculative_file, offset);
         Some(ctx)
     }
 
@@ -245,7 +238,7 @@ impl<'a> CompletionContext<'a> {
     ///   Exception for this case is `impl Trait for Foo`, where we would like to hint trait method names.
     /// - `for _ i$0` -- obviously, it'll be "in" keyword.
     pub(crate) fn no_completion_required(&self) -> bool {
-        (self.fn_is_prev && !self.inside_impl_trait_block) || self.for_is_prev2
+        self.no_completion_required
     }
 
     /// The range of the identifier that is being completed.
@@ -264,33 +257,85 @@ impl<'a> CompletionContext<'a> {
         }
     }
 
+    pub(crate) fn previous_token_is(&self, kind: SyntaxKind) -> bool {
+        self.previous_token.as_ref().map_or(false, |tok| tok.kind() == kind)
+    }
+
+    pub(crate) fn expects_assoc_item(&self) -> bool {
+        matches!(
+            self.completion_location,
+            Some(ImmediateLocation::Trait) | Some(ImmediateLocation::Impl)
+        )
+    }
+
+    pub(crate) fn expects_use_tree(&self) -> bool {
+        matches!(self.completion_location, Some(ImmediateLocation::Use))
+    }
+
+    pub(crate) fn expects_non_trait_assoc_item(&self) -> bool {
+        matches!(self.completion_location, Some(ImmediateLocation::Impl))
+    }
+
+    pub(crate) fn expects_item(&self) -> bool {
+        matches!(self.completion_location, Some(ImmediateLocation::ItemList))
+    }
+
+    pub(crate) fn expects_expression(&self) -> bool {
+        self.is_expr
+    }
+
+    pub(crate) fn has_block_expr_parent(&self) -> bool {
+        matches!(self.completion_location, Some(ImmediateLocation::BlockExpr))
+    }
+
+    pub(crate) fn expects_ident_pat_or_ref_expr(&self) -> bool {
+        matches!(
+            self.completion_location,
+            Some(ImmediateLocation::IdentPat) | Some(ImmediateLocation::RefExpr)
+        )
+    }
+
+    pub(crate) fn expect_record_field(&self) -> bool {
+        matches!(self.completion_location, Some(ImmediateLocation::RecordField))
+    }
+
+    pub(crate) fn has_impl_or_trait_prev_sibling(&self) -> bool {
+        matches!(
+            self.prev_sibling,
+            Some(ImmediatePrevSibling::ImplDefType) | Some(ImmediatePrevSibling::TraitDefName)
+        )
+    }
+
+    pub(crate) fn after_if(&self) -> bool {
+        matches!(self.prev_sibling, Some(ImmediatePrevSibling::IfExpr))
+    }
+
+    pub(crate) fn is_path_disallowed(&self) -> bool {
+        self.record_lit_syntax.is_some()
+            || self.record_pat_syntax.is_some()
+            || self.attribute_under_caret.is_some()
+            || self.mod_declaration_under_caret.is_some()
+    }
+
     fn fill_keyword_patterns(&mut self, file_with_fake_ident: &SyntaxNode, offset: TextSize) {
         let fake_ident_token = file_with_fake_ident.token_at_offset(offset).right_biased().unwrap();
         let syntax_element = NodeOrToken::Token(fake_ident_token);
-        self.block_expr_parent = has_block_expr_parent(syntax_element.clone());
-        self.unsafe_is_prev = unsafe_is_prev(syntax_element.clone());
-        self.if_is_prev = if_is_prev(syntax_element.clone());
-        self.bind_pat_parent = has_bind_pat_parent(syntax_element.clone());
-        self.ref_pat_parent = has_ref_parent(syntax_element.clone());
+        self.previous_token = previous_token(syntax_element.clone());
         self.in_loop_body = is_in_loop_body(syntax_element.clone());
-        self.has_trait_parent = has_trait_parent(syntax_element.clone());
-        self.has_impl_parent = has_impl_parent(syntax_element.clone());
-        self.inside_impl_trait_block = inside_impl_trait_block(syntax_element.clone());
-        self.has_field_list_parent = has_field_list_parent(syntax_element.clone());
-        self.impl_as_prev_sibling = has_impl_as_prev_sibling(syntax_element.clone());
-        self.trait_as_prev_sibling = has_trait_as_prev_sibling(syntax_element.clone());
         self.is_match_arm = is_match_arm(syntax_element.clone());
-        self.has_item_list_or_source_file_parent =
-            has_item_list_or_source_file_parent(syntax_element.clone());
+
         self.mod_declaration_under_caret =
             find_node_at_offset::<ast::Module>(&file_with_fake_ident, offset)
                 .filter(|module| module.item_list().is_none());
-        self.for_is_prev2 = for_is_prev2(syntax_element.clone());
-        self.fn_is_prev = fn_is_prev(syntax_element.clone());
         self.incomplete_let =
             syntax_element.ancestors().take(6).find_map(ast::LetStmt::cast).map_or(false, |it| {
                 it.syntax().text_range().end() == syntax_element.text_range().end()
             });
+
+        let inside_impl_trait_block = inside_impl_trait_block(syntax_element.clone());
+        let fn_is_prev = self.previous_token_is(T![fn]);
+        let for_is_prev2 = for_is_prev2(syntax_element.clone());
+        self.no_completion_required = (fn_is_prev && !inside_impl_trait_block) || for_is_prev2;
     }
 
     fn fill_impl_def(&mut self) {
@@ -412,67 +457,21 @@ impl<'a> CompletionContext<'a> {
         self.expected_type = expected_type;
         self.expected_name = expected_name;
         self.attribute_under_caret = find_node_at_offset(&file_with_fake_ident, offset);
-
-        if let Some(lifetime) = find_node_at_offset::<ast::Lifetime>(&file_with_fake_ident, offset)
-        {
-            self.classify_lifetime(original_file, lifetime, offset);
-        }
-
-        // First, let's try to complete a reference to some declaration.
-        if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(&file_with_fake_ident, offset) {
-            // Special case, `trait T { fn foo(i_am_a_name_ref) {} }`.
-            // See RFC#1685.
-            if is_node::<ast::Param>(name_ref.syntax()) {
-                self.is_param = true;
-                return;
-            }
-            // FIXME: remove this (V) duplication and make the check more precise
-            if name_ref.syntax().ancestors().find_map(ast::RecordPatFieldList::cast).is_some() {
-                self.record_pat_syntax =
-                    self.sema.find_node_at_offset_with_macros(&original_file, offset);
-            }
-            self.classify_name_ref(original_file, name_ref, offset);
-        }
-
-        // Otherwise, see if this is a declaration. We can use heuristics to
-        // suggest declaration names, see `CompletionKind::Magic`.
-        if let Some(name) = find_node_at_offset::<ast::Name>(&file_with_fake_ident, offset) {
-            if let Some(bind_pat) = name.syntax().ancestors().find_map(ast::IdentPat::cast) {
-                self.is_pat_binding_or_const = true;
-                if bind_pat.at_token().is_some()
-                    || bind_pat.ref_token().is_some()
-                    || bind_pat.mut_token().is_some()
-                {
-                    self.is_pat_binding_or_const = false;
-                }
-                if bind_pat.syntax().parent().and_then(ast::RecordPatFieldList::cast).is_some() {
-                    self.is_pat_binding_or_const = false;
-                }
-                if let Some(Some(pat)) = bind_pat.syntax().ancestors().find_map(|node| {
-                    match_ast! {
-                        match node {
-                            ast::LetStmt(it) => Some(it.pat()),
-                            ast::Param(it) => Some(it.pat()),
-                            _ => None,
-                        }
-                    }
-                }) {
-                    if pat.syntax().text_range().contains_range(bind_pat.syntax().text_range()) {
-                        self.is_pat_binding_or_const = false;
-                        self.is_irrefutable_pat_binding = true;
-                    }
-                }
-
-                self.fill_impl_def();
+        let name_like = match find_node_at_offset(&&file_with_fake_ident, offset) {
+            Some(it) => it,
+            None => return,
+        };
+        self.completion_location = determine_location(&name_like);
+        self.prev_sibling = determine_prev_sibling(&name_like);
+        match name_like {
+            ast::NameLike::Lifetime(lifetime) => {
+                self.classify_lifetime(original_file, lifetime, offset);
             }
-            if is_node::<ast::Param>(name.syntax()) {
-                self.is_param = true;
-                return;
+            ast::NameLike::NameRef(name_ref) => {
+                self.classify_name_ref(original_file, name_ref, offset);
             }
-            // FIXME: remove this (^) duplication and make the check more precise
-            if name.syntax().ancestors().find_map(ast::RecordPatFieldList::cast).is_some() {
-                self.record_pat_syntax =
-                    self.sema.find_node_at_offset_with_macros(&original_file, offset);
+            ast::NameLike::Name(name) => {
+                self.classify_name(original_file, name, offset);
             }
         }
     }
@@ -506,22 +505,71 @@ impl<'a> CompletionContext<'a> {
         }
     }
 
+    fn classify_name(&mut self, original_file: &SyntaxNode, name: ast::Name, offset: TextSize) {
+        if let Some(bind_pat) = name.syntax().parent().and_then(ast::IdentPat::cast) {
+            self.is_pat_or_const = Some(PatternRefutability::Refutable);
+            // if any of these is here our bind pat can't be a const pat anymore
+            let complex_ident_pat = bind_pat.at_token().is_some()
+                || bind_pat.ref_token().is_some()
+                || bind_pat.mut_token().is_some();
+            if complex_ident_pat {
+                self.is_pat_or_const = None;
+            } else {
+                let irrefutable_pat = bind_pat.syntax().ancestors().find_map(|node| {
+                    match_ast! {
+                        match node {
+                            ast::LetStmt(it) => Some(it.pat()),
+                            ast::Param(it) => Some(it.pat()),
+                            _ => None,
+                        }
+                    }
+                });
+                if let Some(Some(pat)) = irrefutable_pat {
+                    // This check is here since we could be inside a pattern in the initializer expression of the let statement.
+                    if pat.syntax().text_range().contains_range(bind_pat.syntax().text_range()) {
+                        self.is_pat_or_const = Some(PatternRefutability::Irrefutable);
+                    }
+                }
+
+                let is_name_in_field_pat = bind_pat
+                    .syntax()
+                    .parent()
+                    .and_then(ast::RecordPatField::cast)
+                    .map_or(false, |pat_field| pat_field.name_ref().is_none());
+                if is_name_in_field_pat {
+                    self.is_pat_or_const = None;
+                }
+            }
+
+            self.fill_impl_def();
+        }
+        self.is_param |= is_node::<ast::Param>(name.syntax());
+        if ast::RecordPatField::for_field_name(&name).is_some() {
+            self.record_pat_syntax =
+                self.sema.find_node_at_offset_with_macros(&original_file, offset);
+        }
+    }
+
     fn classify_name_ref(
         &mut self,
         original_file: &SyntaxNode,
         name_ref: ast::NameRef,
         offset: TextSize,
     ) {
-        self.name_ref_syntax =
-            find_node_at_offset(original_file, name_ref.syntax().text_range().start());
-        let name_range = name_ref.syntax().text_range();
+        self.fill_impl_def();
         if ast::RecordExprField::for_field_name(&name_ref).is_some() {
             self.record_lit_syntax =
                 self.sema.find_node_at_offset_with_macros(original_file, offset);
         }
+        if ast::RecordPatField::for_field_name_ref(&name_ref).is_some() {
+            self.record_pat_syntax =
+                self.sema.find_node_at_offset_with_macros(&original_file, offset);
+        }
 
-        self.fill_impl_def();
+        self.name_ref_syntax =
+            find_node_at_offset(original_file, name_ref.syntax().text_range().start());
 
+        let name_range = name_ref.syntax().text_range();
         let top_node = name_ref
             .syntax()
             .ancestors()
@@ -529,31 +577,20 @@ impl<'a> CompletionContext<'a> {
             .last()
             .unwrap();
 
-        match top_node.parent().map(|it| it.kind()) {
-            Some(SOURCE_FILE) | Some(ITEM_LIST) => {
-                self.is_new_item = true;
-                return;
-            }
-            _ => (),
+        if matches!(top_node.parent().map(|it| it.kind()), Some(SOURCE_FILE) | Some(ITEM_LIST)) {
+            self.is_new_item = true;
+            return;
         }
 
         self.use_item_syntax =
             self.sema.token_ancestors_with_macros(self.token.clone()).find_map(ast::Use::cast);
 
-        self.function_syntax = self
+        self.function_def = self
             .sema
             .token_ancestors_with_macros(self.token.clone())
             .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
             .find_map(ast::Fn::cast);
 
-        self.record_field_syntax = self
-            .sema
-            .token_ancestors_with_macros(self.token.clone())
-            .take_while(|it| {
-                it.kind() != SOURCE_FILE && it.kind() != MODULE && it.kind() != CALL_EXPR
-            })
-            .find_map(ast::RecordExprField::cast);
-
         let parent = match name_ref.syntax().parent() {
             Some(it) => it,
             None => return,
@@ -614,18 +651,8 @@ impl<'a> CompletionContext<'a> {
                 })
                 .unwrap_or(false);
             self.is_expr = path.syntax().parent().and_then(ast::PathExpr::cast).is_some();
-
-            if let Some(off) = name_ref.syntax().text_range().start().checked_sub(2.into()) {
-                if let Some(if_expr) =
-                    self.sema.find_node_at_offset_with_macros::<ast::IfExpr>(original_file, off)
-                {
-                    if if_expr.syntax().text_range().end() < name_ref.syntax().text_range().start()
-                    {
-                        self.after_if = true;
-                    }
-                }
-            }
         }
+
         if let Some(field_expr) = ast::FieldExpr::cast(parent.clone()) {
             // The receiver comes before the point of insertion of the fake
             // ident, so it should have the same range in the non-modified file
@@ -643,6 +670,7 @@ impl<'a> CompletionContext<'a> {
                     false
                 };
         }
+
         if let Some(method_call_expr) = ast::MethodCallExpr::cast(parent) {
             // As above
             self.dot_receiver = method_call_expr