Move completion to ra_analysis

While we should handle completion for isolated file, it's better
achieved by using empty Analysis, rather than working only with &File:
we need memoization for type inference even inside a single file.

6 files changed, 711 insertions, 63 deletions

diff --git a/crates/ra_analysis/src/completion.rs b/crates/ra_analysis/src/completion.rs
index 869ab5afb..340ae3f66 100644
--- a/crates/ra_analysis/src/completion.rs
+++ b/crates/ra_analysis/src/completion.rs
@@ -1,7 +1,10 @@
-use ra_editor::{CompletionItem, find_node_at_offset};
+use rustc_hash::{FxHashMap, FxHashSet};
+use ra_editor::{find_node_at_offset};
 use ra_syntax::{
-    AtomEdit, File, TextUnit, AstNode,
-    ast,
+    AtomEdit, File, TextUnit, AstNode, SyntaxNodeRef,
+    algo::visit::{visitor, visitor_ctx, Visitor, VisitorCtx},
+    ast::{self, AstChildren, LoopBodyOwner, ModuleItemOwner},
+    SyntaxKind::*,
 };
 
 use crate::{
@@ -9,9 +12,21 @@ use crate::{
     input::FilesDatabase,
     db::{self, SyntaxDatabase},
     descriptors::DescriptorDatabase,
-    descriptors::module::{ModuleTree, ModuleId},
+    descriptors::function::FnScopes,
+    descriptors::module::{ModuleTree, ModuleId, ModuleScope},
 };
 
+
+#[derive(Debug)]
+pub struct CompletionItem {
+    /// What user sees in pop-up
+    pub label: String,
+    /// What string is used for filtering, defaults to label
+    pub lookup: Option<String>,
+    /// What is inserted, defaults to label
+    pub snippet: Option<String>,
+}
+
 pub(crate) fn resolve_based_completion(db: &db::RootDatabase, file_id: FileId, offset: TextUnit) -> Cancelable<Option<Vec<CompletionItem>>> {
     let source_root_id = db.file_source_root(file_id);
     let file = db.file_syntax(file_id);
@@ -73,3 +88,602 @@ fn crate_path(name_ref: ast::NameRef) -> Option<Vec<ast::NameRef>> {
     res.reverse();
     Some(res)
 }
+
+
+pub(crate) fn scope_completion(
+    db: &db::RootDatabase,
+    file_id: FileId,
+    offset: TextUnit,
+) -> Option<Vec<CompletionItem>> {
+    let original_file = db.file_syntax(file_id);
+    // Insert a fake ident to get a valid parse tree
+    let file = {
+        let edit = AtomEdit::insert(offset, "intellijRulezz".to_string());
+        original_file.reparse(&edit)
+    };
+    let mut has_completions = false;
+    let mut res = Vec::new();
+    if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(file.syntax(), offset) {
+        has_completions = true;
+        complete_name_ref(&file, name_ref, &mut res);
+        // special case, `trait T { fn foo(i_am_a_name_ref) {} }`
+        if is_node::<ast::Param>(name_ref.syntax()) {
+            param_completions(name_ref.syntax(), &mut res);
+        }
+        let name_range = name_ref.syntax().range();
+        let top_node = name_ref
+            .syntax()
+            .ancestors()
+            .take_while(|it| it.range() == name_range)
+            .last()
+            .unwrap();
+        match top_node.parent().map(|it| it.kind()) {
+            Some(ROOT) | Some(ITEM_LIST) => complete_mod_item_snippets(&mut res),
+            _ => (),
+        }
+    }
+    if let Some(name) = find_node_at_offset::<ast::Name>(file.syntax(), offset) {
+        if is_node::<ast::Param>(name.syntax()) {
+            has_completions = true;
+            param_completions(name.syntax(), &mut res);
+        }
+    }
+    if has_completions {
+        Some(res)
+    } else {
+        None
+    }
+}
+
+fn complete_module_items(
+    file: &File,
+    items: AstChildren<ast::ModuleItem>,
+    this_item: Option<ast::NameRef>,
+    acc: &mut Vec<CompletionItem>,
+) {
+    let scope = ModuleScope::from_items(items);
+    acc.extend(
+        scope
+            .entries()
+            .iter()
+            .filter(|entry| {
+                let syntax = entry.ptr().resolve(file);
+                Some(syntax.borrowed()) != this_item.map(|it| it.syntax())
+            })
+            .map(|entry| CompletionItem {
+                label: entry.name().to_string(),
+                lookup: None,
+                snippet: None,
+            }),
+    );
+}
+
+fn complete_name_ref(
+    file: &File,
+    name_ref: ast::NameRef,
+    acc: &mut Vec<CompletionItem>,
+) {
+    if !is_node::<ast::Path>(name_ref.syntax()) {
+        return;
+    }
+    let mut visited_fn = false;
+    for node in name_ref.syntax().ancestors() {
+        if let Some(items) = visitor()
+            .visit::<ast::Root, _>(|it| Some(it.items()))
+            .visit::<ast::Module, _>(|it| Some(it.item_list()?.items()))
+            .accept(node)
+        {
+            if let Some(items) = items {
+                complete_module_items(file, items, Some(name_ref), acc);
+            }
+            break;
+        } else if !visited_fn {
+            if let Some(fn_def) = ast::FnDef::cast(node) {
+                visited_fn = true;
+                complete_expr_keywords(&file, fn_def, name_ref, acc);
+                complete_expr_snippets(acc);
+                let scopes = FnScopes::new(fn_def);
+                complete_fn(name_ref, &scopes, acc);
+            }
+        }
+    }
+}
+
+fn param_completions(ctx: SyntaxNodeRef, acc: &mut Vec<CompletionItem>) {
+    let mut params = FxHashMap::default();
+    for node in ctx.ancestors() {
+        let _ = visitor_ctx(&mut params)
+            .visit::<ast::Root, _>(process)
+            .visit::<ast::ItemList, _>(process)
+            .accept(node);
+    }
+    params
+        .into_iter()
+        .filter_map(|(label, (count, param))| {
+            let lookup = param.pat()?.syntax().text().to_string();
+            if count < 2 {
+                None
+            } else {
+                Some((label, lookup))
+            }
+        })
+        .for_each(|(label, lookup)| {
+            acc.push(CompletionItem {
+                label,
+                lookup: Some(lookup),
+                snippet: None,
+            })
+        });
+
+    fn process<'a, N: ast::FnDefOwner<'a>>(
+        node: N,
+        params: &mut FxHashMap<String, (u32, ast::Param<'a>)>,
+    ) {
+        node.functions()
+            .filter_map(|it| it.param_list())
+            .flat_map(|it| it.params())
+            .for_each(|param| {
+                let text = param.syntax().text().to_string();
+                params.entry(text).or_insert((0, param)).0 += 1;
+            })
+    }
+}
+
+fn is_node<'a, N: AstNode<'a>>(node: SyntaxNodeRef<'a>) -> bool {
+    match node.ancestors().filter_map(N::cast).next() {
+        None => false,
+        Some(n) => n.syntax().range() == node.range(),
+    }
+}
+
+fn complete_expr_keywords(
+    file: &File,
+    fn_def: ast::FnDef,
+    name_ref: ast::NameRef,
+    acc: &mut Vec<CompletionItem>,
+) {
+    acc.push(keyword("if", "if $0 {}"));
+    acc.push(keyword("match", "match $0 {}"));
+    acc.push(keyword("while", "while $0 {}"));
+    acc.push(keyword("loop", "loop {$0}"));
+
+    if let Some(off) = name_ref.syntax().range().start().checked_sub(2.into()) {
+        if let Some(if_expr) = find_node_at_offset::<ast::IfExpr>(file.syntax(), off) {
+            if if_expr.syntax().range().end() < name_ref.syntax().range().start() {
+                acc.push(keyword("else", "else {$0}"));
+                acc.push(keyword("else if", "else if $0 {}"));
+            }
+        }
+    }
+    if is_in_loop_body(name_ref) {
+        acc.push(keyword("continue", "continue"));
+        acc.push(keyword("break", "break"));
+    }
+    acc.extend(complete_return(fn_def, name_ref));
+}
+
+fn is_in_loop_body(name_ref: ast::NameRef) -> bool {
+    for node in name_ref.syntax().ancestors() {
+        if node.kind() == FN_DEF || node.kind() == LAMBDA_EXPR {
+            break;
+        }
+        let loop_body = visitor()
+            .visit::<ast::ForExpr, _>(LoopBodyOwner::loop_body)
+            .visit::<ast::WhileExpr, _>(LoopBodyOwner::loop_body)
+            .visit::<ast::LoopExpr, _>(LoopBodyOwner::loop_body)
+            .accept(node);
+        if let Some(Some(body)) = loop_body {
+            if name_ref.syntax().range().is_subrange(&body.syntax().range()) {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+fn complete_return(fn_def: ast::FnDef, name_ref: ast::NameRef) -> Option<CompletionItem> {
+    // let is_last_in_block = name_ref.syntax().ancestors().filter_map(ast::Expr::cast)
+    //     .next()
+    //     .and_then(|it| it.syntax().parent())
+    //     .and_then(ast::Block::cast)
+    //     .is_some();
+
+    // if is_last_in_block {
+    //     return None;
+    // }
+
+    let is_stmt = match name_ref
+        .syntax()
+        .ancestors()
+        .filter_map(ast::ExprStmt::cast)
+        .next()
+    {
+        None => false,
+        Some(expr_stmt) => expr_stmt.syntax().range() == name_ref.syntax().range(),
+    };
+    let snip = match (is_stmt, fn_def.ret_type().is_some()) {
+        (true, true) => "return $0;",
+        (true, false) => "return;",
+        (false, true) => "return $0",
+        (false, false) => "return",
+    };
+    Some(keyword("return", snip))
+}
+
+fn keyword(kw: &str, snip: &str) -> CompletionItem {
+    CompletionItem {
+        label: kw.to_string(),
+        lookup: None,
+        snippet: Some(snip.to_string()),
+    }
+}
+
+fn complete_expr_snippets(acc: &mut Vec<CompletionItem>) {
+    acc.push(CompletionItem {
+        label: "pd".to_string(),
+        lookup: None,
+        snippet: Some("eprintln!(\"$0 = {:?}\", $0);".to_string()),
+    });
+    acc.push(CompletionItem {
+        label: "ppd".to_string(),
+        lookup: None,
+        snippet: Some("eprintln!(\"$0 = {:#?}\", $0);".to_string()),
+    });
+}
+
+fn complete_mod_item_snippets(acc: &mut Vec<CompletionItem>) {
+    acc.push(CompletionItem {
+        label: "tfn".to_string(),
+        lookup: None,
+        snippet: Some("#[test]\nfn $1() {\n    $0\n}".to_string()),
+    });
+    acc.push(CompletionItem {
+        label: "pub(crate)".to_string(),
+        lookup: None,
+        snippet: Some("pub(crate) $0".to_string()),
+    })
+}
+
+fn complete_fn(name_ref: ast::NameRef, scopes: &FnScopes, acc: &mut Vec<CompletionItem>) {
+    let mut shadowed = FxHashSet::default();
+    acc.extend(
+        scopes
+            .scope_chain(name_ref.syntax())
+            .flat_map(|scope| scopes.entries(scope).iter())
+            .filter(|entry| shadowed.insert(entry.name()))
+            .map(|entry| CompletionItem {
+                label: entry.name().to_string(),
+                lookup: None,
+                snippet: None,
+            }),
+    );
+    if scopes.self_param.is_some() {
+        acc.push(CompletionItem {
+            label: "self".to_string(),
+            lookup: None,
+            snippet: None,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::{assert_eq_dbg, extract_offset};
+
+    use crate::FileId;
+    use crate::mock_analysis::MockAnalysis;
+
+    use super::*;
+
+    fn check_scope_completion(code: &str, expected_completions: &str) {
+        let (off, code) = extract_offset(&code);
+        let analysis = MockAnalysis::with_files(&[("/main.rs", &code)]).analysis();
+        let file_id = FileId(1);
+        let completions = scope_completion(&analysis.imp.db, file_id, off)
+            .unwrap()
+            .into_iter()
+            .filter(|c| c.snippet.is_none())
+            .collect::<Vec<_>>();
+        assert_eq_dbg(expected_completions, &completions);
+    }
+
+    fn check_snippet_completion(code: &str, expected_completions: &str) {
+        let (off, code) = extract_offset(&code);
+        let analysis = MockAnalysis::with_files(&[("/main.rs", &code)]).analysis();
+        let file_id = FileId(1);
+        let completions = scope_completion(&analysis.imp.db, file_id, off)
+            .unwrap()
+            .into_iter()
+            .filter(|c| c.snippet.is_some())
+            .collect::<Vec<_>>();
+        assert_eq_dbg(expected_completions, &completions);
+    }
+
+    #[test]
+    fn test_completion_let_scope() {
+        check_scope_completion(
+            r"
+            fn quux(x: i32) {
+                let y = 92;
+                1 + <|>;
+                let z = ();
+            }
+            ",
+            r#"[CompletionItem { label: "y", lookup: None, snippet: None },
+                   CompletionItem { label: "x", lookup: None, snippet: None },
+                   CompletionItem { label: "quux", lookup: None, snippet: None }]"#,
+        );
+    }
+
+    #[test]
+    fn test_completion_if_let_scope() {
+        check_scope_completion(
+            r"
+            fn quux() {
+                if let Some(x) = foo() {
+                    let y = 92;
+                };
+                if let Some(a) = bar() {
+                    let b = 62;
+                    1 + <|>
+                }
+            }
+            ",
+            r#"[CompletionItem { label: "b", lookup: None, snippet: None },
+                   CompletionItem { label: "a", lookup: None, snippet: None },
+                   CompletionItem { label: "quux", lookup: None, snippet: None }]"#,
+        );
+    }
+
+    #[test]
+    fn test_completion_for_scope() {
+        check_scope_completion(
+            r"
+            fn quux() {
+                for x in &[1, 2, 3] {
+                    <|>
+                }
+            }
+            ",
+            r#"[CompletionItem { label: "x", lookup: None, snippet: None },
+                   CompletionItem { label: "quux", lookup: None, snippet: None }]"#,
+        );
+    }
+
+    #[test]
+    fn test_completion_mod_scope() {
+        check_scope_completion(
+            r"
+            struct Foo;
+            enum Baz {}
+            fn quux() {
+                <|>
+            }
+            ",
+            r#"[CompletionItem { label: "Foo", lookup: None, snippet: None },
+                   CompletionItem { label: "Baz", lookup: None, snippet: None },
+                   CompletionItem { label: "quux", lookup: None, snippet: None }]"#,
+        );
+    }
+
+    #[test]
+    fn test_completion_mod_scope_no_self_use() {
+        check_scope_completion(
+            r"
+            use foo<|>;
+            ",
+            r#"[]"#,
+        );
+    }
+
+    #[test]
+    fn test_completion_mod_scope_nested() {
+        check_scope_completion(
+            r"
+            struct Foo;
+            mod m {
+                struct Bar;
+                fn quux() { <|> }
+            }
+            ",
+            r#"[CompletionItem { label: "Bar", lookup: None, snippet: None },
+                   CompletionItem { label: "quux", lookup: None, snippet: None }]"#,
+        );
+    }
+
+    #[test]
+    fn test_complete_type() {
+        check_scope_completion(
+            r"
+            struct Foo;
+            fn x() -> <|>
+        ",
+            r#"[CompletionItem { label: "Foo", lookup: None, snippet: None },
+               CompletionItem { label: "x", lookup: None, snippet: None }]"#,
+        )
+    }
+
+    #[test]
+    fn test_complete_shadowing() {
+        check_scope_completion(
+            r"
+            fn foo() -> {
+                let bar = 92;
+                {
+                    let bar = 62;
+                    <|>
+                }
+            }
+        ",
+            r#"[CompletionItem { label: "bar", lookup: None, snippet: None },
+               CompletionItem { label: "foo", lookup: None, snippet: None }]"#,
+        )
+    }
+
+    #[test]
+    fn test_complete_self() {
+        check_scope_completion(
+            r"
+            impl S { fn foo(&self) { <|> } }
+        ",
+            r#"[CompletionItem { label: "self", lookup: None, snippet: None }]"#,
+        )
+    }
+
+    #[test]
+    fn test_completion_kewords() {
+        check_snippet_completion(r"
+            fn quux() {
+                <|>
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+    }
+
+    #[test]
+    fn test_completion_else() {
+        check_snippet_completion(r"
+            fn quux() {
+                if true {
+                    ()
+                } <|>
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "else", lookup: None, snippet: Some("else {$0}") },
+                   CompletionItem { label: "else if", lookup: None, snippet: Some("else if $0 {}") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+    }
+
+    #[test]
+    fn test_completion_return_value() {
+        check_snippet_completion(r"
+            fn quux() -> i32 {
+                <|>
+                92
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return $0;") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+        check_snippet_completion(r"
+            fn quux() {
+                <|>
+                92
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return;") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+    }
+
+    #[test]
+    fn test_completion_return_no_stmt() {
+        check_snippet_completion(r"
+            fn quux() -> i32 {
+                match () {
+                    () => <|>
+                }
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return $0") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+    }
+
+    #[test]
+    fn test_continue_break_completion() {
+        check_snippet_completion(r"
+            fn quux() -> i32 {
+                loop { <|> }
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "continue", lookup: None, snippet: Some("continue") },
+                   CompletionItem { label: "break", lookup: None, snippet: Some("break") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return $0") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+        check_snippet_completion(r"
+            fn quux() -> i32 {
+                loop { || { <|> } }
+            }
+            ", r#"[CompletionItem { label: "if", lookup: None, snippet: Some("if $0 {}") },
+                   CompletionItem { label: "match", lookup: None, snippet: Some("match $0 {}") },
+                   CompletionItem { label: "while", lookup: None, snippet: Some("while $0 {}") },
+                   CompletionItem { label: "loop", lookup: None, snippet: Some("loop {$0}") },
+                   CompletionItem { label: "return", lookup: None, snippet: Some("return $0") },
+                   CompletionItem { label: "pd", lookup: None, snippet: Some("eprintln!(\"$0 = {:?}\", $0);") },
+                   CompletionItem { label: "ppd", lookup: None, snippet: Some("eprintln!(\"$0 = {:#?}\", $0);") }]"#);
+    }
+
+    #[test]
+    fn test_param_completion_last_param() {
+        check_scope_completion(r"
+            fn foo(file_id: FileId) {}
+            fn bar(file_id: FileId) {}
+            fn baz(file<|>) {}
+        ", r#"[CompletionItem { label: "file_id: FileId", lookup: Some("file_id"), snippet: None }]"#);
+    }
+
+    #[test]
+    fn test_param_completion_nth_param() {
+        check_scope_completion(r"
+            fn foo(file_id: FileId) {}
+            fn bar(file_id: FileId) {}
+            fn baz(file<|>, x: i32) {}
+        ", r#"[CompletionItem { label: "file_id: FileId", lookup: Some("file_id"), snippet: None }]"#);
+    }
+
+    #[test]
+    fn test_param_completion_trait_param() {
+        check_scope_completion(r"
+            pub(crate) trait SourceRoot {
+                pub fn contains(&self, file_id: FileId) -> bool;
+                pub fn module_map(&self) -> &ModuleMap;
+                pub fn lines(&self, file_id: FileId) -> &LineIndex;
+                pub fn syntax(&self, file<|>)
+            }
+        ", r#"[CompletionItem { label: "self", lookup: None, snippet: None },
+               CompletionItem { label: "SourceRoot", lookup: None, snippet: None },
+               CompletionItem { label: "file_id: FileId", lookup: Some("file_id"), snippet: None }]"#);
+    }
+
+    #[test]
+    fn test_item_snippets() {
+        // check_snippet_completion(r"
+        //     <|>
+        //     ",
+        //     r##"[CompletionItem { label: "tfn", lookup: None, snippet: Some("#[test]\nfn $1() {\n    $0\n}") }]"##,
+        // );
+        check_snippet_completion(r"
+            #[cfg(test)]
+            mod tests {
+                <|>
+            }
+            ",
+            r##"[CompletionItem { label: "tfn", lookup: None, snippet: Some("#[test]\nfn $1() {\n    $0\n}") },
+                 CompletionItem { label: "pub(crate)", lookup: None, snippet: Some("pub(crate) $0") }]"##,
+        );
+    }
+}
diff --git a/crates/ra_analysis/src/descriptors/module/scope.rs b/crates/ra_analysis/src/descriptors/module/scope.rs
index 0f8f325ab..846b8b44f 100644
--- a/crates/ra_analysis/src/descriptors/module/scope.rs
+++ b/crates/ra_analysis/src/descriptors/module/scope.rs
@@ -30,8 +30,12 @@ enum EntryKind {
 
 impl ModuleScope {
     pub fn new(file: &File) -> ModuleScope {
+        ModuleScope::from_items(file.ast().items())
+    }
+
+    pub fn from_items<'a>(items: impl Iterator<Item = ast::ModuleItem<'a>>) -> ModuleScope {
         let mut entries = Vec::new();
-        for item in file.ast().items() {
+        for item in items {
             let entry = match item {
                 ast::ModuleItem::StructDef(item) => Entry::new(item),
                 ast::ModuleItem::EnumDef(item) => Entry::new(item),
diff --git a/crates/ra_analysis/src/imp.rs b/crates/ra_analysis/src/imp.rs
index 6473a1dbc..38d4b6a23 100644
--- a/crates/ra_analysis/src/imp.rs
+++ b/crates/ra_analysis/src/imp.rs
@@ -3,7 +3,7 @@ use std::{
     sync::Arc,
 };
 
-use ra_editor::{self, find_node_at_offset, FileSymbol, LineIndex, LocalEdit, CompletionItem};
+use ra_editor::{self, find_node_at_offset, FileSymbol, LineIndex, LocalEdit};
 use ra_syntax::{
     ast::{self, ArgListOwner, Expr, NameOwner},
     AstNode, File, SmolStr,
@@ -26,6 +26,7 @@ use crate::{
         module::{ModuleTree, Problem},
         function::{FnDescriptor, FnId},
     },
+    completion::{scope_completion, resolve_based_completion, CompletionItem},
     symbol_index::SymbolIndex,
     syntax_ptr::SyntaxPtrDatabase,
     CrateGraph, CrateId, Diagnostic, FileId, FileResolver, FileSystemEdit, Position,
@@ -179,7 +180,7 @@ impl AnalysisHostImpl {
 
 #[derive(Debug)]
 pub(crate) struct AnalysisImpl {
-    db: db::RootDatabase,
+    pub(crate) db: db::RootDatabase,
 }
 
 impl AnalysisImpl {
@@ -249,12 +250,11 @@ impl AnalysisImpl {
     pub fn completions(&self, file_id: FileId, offset: TextUnit) -> Cancelable<Option<Vec<CompletionItem>>> {
         let mut res = Vec::new();
         let mut has_completions = false;
-        let file = self.file_syntax(file_id);
-        if let Some(scope_based) = ra_editor::scope_completion(&file, offset) {
+        if let Some(scope_based) = scope_completion(&self.db, file_id, offset) {
             res.extend(scope_based);
             has_completions = true;
         }
-        if let Some(scope_based) = crate::completion::resolve_based_completion(&self.db, file_id, offset)? {
+        if let Some(scope_based) = resolve_based_completion(&self.db, file_id, offset)? {
             res.extend(scope_based);
             has_completions = true;
         }
diff --git a/crates/ra_analysis/src/lib.rs b/crates/ra_analysis/src/lib.rs
index a77c9a5fa..776010281 100644
--- a/crates/ra_analysis/src/lib.rs
+++ b/crates/ra_analysis/src/lib.rs
@@ -13,6 +13,7 @@ mod imp;
 mod symbol_index;
 mod completion;
 mod syntax_ptr;
+mod mock_analysis;
 
 use std::{
     fmt,
@@ -30,10 +31,12 @@ use crate::{
 
 pub use crate::{
     descriptors::function::FnDescriptor,
-    input::{FileId, FileResolver, CrateGraph, CrateId}
+    completion::CompletionItem,
+    input::{FileId, FileResolver, CrateGraph, CrateId},
+    mock_analysis::MockAnalysis,
 };
 pub use ra_editor::{
-    CompletionItem, FileSymbol, Fold, FoldKind, HighlightedRange, LineIndex, Runnable,
+    FileSymbol, Fold, FoldKind, HighlightedRange, LineIndex, Runnable,
     RunnableKind, StructureNode,
 };
 
@@ -197,7 +200,7 @@ impl Query {
 
 #[derive(Debug)]
 pub struct Analysis {
-    imp: AnalysisImpl,
+    pub(crate) imp: AnalysisImpl,
 }
 
 impl Analysis {
diff --git a/crates/ra_analysis/src/mock_analysis.rs b/crates/ra_analysis/src/mock_analysis.rs
new file mode 100644
index 000000000..1c1dbee7c
--- /dev/null
+++ b/crates/ra_analysis/src/mock_analysis.rs
@@ -0,0 +1,71 @@
+
+use std::sync::Arc;
+
+use relative_path::{RelativePath, RelativePathBuf};
+
+use crate::{
+    AnalysisChange, Analysis, AnalysisHost, FileId, FileResolver,
+};
+
+/// Mock analysis is used in test to bootstrap an AnalysisHost/Analysis
+/// from a set of in-memory files.
+#[derive(Debug, Default)]
+pub struct MockAnalysis {
+    files: Vec<(String, String)>,
+}
+
+impl MockAnalysis {
+    pub fn new() -> MockAnalysis {
+        MockAnalysis::default()
+    }
+    pub fn with_files(files: &[(&str, &str)]) -> MockAnalysis {
+        let files = files.iter()
+            .map(|it| (it.0.to_string(), it.1.to_string()))
+            .collect();
+        MockAnalysis { files }
+    }
+    pub fn analysis_host(self) -> AnalysisHost {
+        let mut host = AnalysisHost::new();
+        let mut file_map = Vec::new();
+        let mut change = AnalysisChange::new();
+        for (id, (path, contents)) in self.files.into_iter().enumerate() {
+            let file_id = FileId((id + 1) as u32);
+            assert!(path.starts_with('/'));
+            let path = RelativePathBuf::from_path(&path[1..]).unwrap();
+            change.add_file(file_id, contents);
+            file_map.push((file_id, path));
+        }
+        change.set_file_resolver(Arc::new(FileMap(file_map)));
+        host.apply_change(change);
+        host
+    }
+    pub fn analysis(self) -> Analysis {
+        self.analysis_host().analysis()
+    }
+}
+
+#[derive(Debug)]
+struct FileMap(Vec<(FileId, RelativePathBuf)>);
+
+impl FileMap {
+    fn iter<'a>(&'a self) -> impl Iterator<Item = (FileId, &'a RelativePath)> + 'a {
+        self.0
+            .iter()
+            .map(|(id, path)| (*id, path.as_relative_path()))
+    }
+
+    fn path(&self, id: FileId) -> &RelativePath {
+        self.iter().find(|&(it, _)| it == id).unwrap().1
+    }
+}
+
+impl FileResolver for FileMap {
+    fn file_stem(&self, id: FileId) -> String {
+        self.path(id).file_stem().unwrap().to_string()
+    }
+    fn resolve(&self, id: FileId, rel: &RelativePath) -> Option<FileId> {
+        let path = self.path(id).join(rel).normalize();
+        let id = self.iter().find(|&(_, p)| path == p)?.0;
+        Some(id)
+    }
+}
diff --git a/crates/ra_analysis/tests/tests.rs b/crates/ra_analysis/tests/tests.rs
index 806e1fb34..f5683aec5 100644
--- a/crates/ra_analysis/tests/tests.rs
+++ b/crates/ra_analysis/tests/tests.rs
@@ -5,62 +5,16 @@ extern crate relative_path;
 extern crate rustc_hash;
 extern crate test_utils;
 
-use std::{
-    sync::Arc,
-};
-
 use ra_syntax::TextRange;
-use relative_path::{RelativePath, RelativePathBuf};
 use test_utils::{assert_eq_dbg, extract_offset};
 
 use ra_analysis::{
-    AnalysisChange, Analysis, AnalysisHost, CrateGraph, CrateId, FileId, FileResolver, FnDescriptor,
+    MockAnalysis,
+    AnalysisChange, Analysis, CrateGraph, CrateId, FileId, FnDescriptor,
 };
 
-#[derive(Debug)]
-struct FileMap(Vec<(FileId, RelativePathBuf)>);
-
-impl FileMap {
-    fn iter<'a>(&'a self) -> impl Iterator<Item = (FileId, &'a RelativePath)> + 'a {
-        self.0
-            .iter()
-            .map(|(id, path)| (*id, path.as_relative_path()))
-    }
-
-    fn path(&self, id: FileId) -> &RelativePath {
-        self.iter().find(|&(it, _)| it == id).unwrap().1
-    }
-}
-
-impl FileResolver for FileMap {
-    fn file_stem(&self, id: FileId) -> String {
-        self.path(id).file_stem().unwrap().to_string()
-    }
-    fn resolve(&self, id: FileId, rel: &RelativePath) -> Option<FileId> {
-        let path = self.path(id).join(rel).normalize();
-        let id = self.iter().find(|&(_, p)| path == p)?.0;
-        Some(id)
-    }
-}
-
-fn analysis_host(files: &[(&str, &str)]) -> AnalysisHost {
-    let mut host = AnalysisHost::new();
-    let mut file_map = Vec::new();
-    let mut change = AnalysisChange::new();
-    for (id, &(path, contents)) in files.iter().enumerate() {
-        let file_id = FileId((id + 1) as u32);
-        assert!(path.starts_with('/'));
-        let path = RelativePathBuf::from_path(&path[1..]).unwrap();
-        change.add_file(file_id, contents.to_string());
-        file_map.push((file_id, path));
-    }
-    change.set_file_resolver(Arc::new(FileMap(file_map)));
-    host.apply_change(change);
-    host
-}
-
 fn analysis(files: &[(&str, &str)]) -> Analysis {
-    analysis_host(files).analysis()
+    MockAnalysis::with_files(files).analysis()
 }
 
 fn get_signature(text: &str) -> (FnDescriptor, Option<usize>) {
@@ -125,7 +79,9 @@ fn test_resolve_parent_module() {
 
 #[test]
 fn test_resolve_crate_root() {
-    let mut host = analysis_host(&[("/lib.rs", "mod foo;"), ("/foo.rs", "")]);
+    let mut host = MockAnalysis::with_files(
+        &[("/lib.rs", "mod foo;"), ("/foo.rs", "")]
+    ).analysis_host();
     let snap = host.analysis();
     assert!(snap.crate_for(FileId(2)).unwrap().is_empty());