8 files changed, 1404 insertions, 0 deletions
diff --git a/crates/ra_ide_api/src/completion/complete_dot.rs b/crates/ra_ide_api/src/completion/complete_dot.rs
new file mode 100644
index 000000000..5d4e60dc5
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_dot.rs
@@ -0,0 +1,121 @@
+use hir::{Ty, Def};
+use crate::Cancelable;
+use crate::completion::{CompletionContext, Completions, CompletionKind, CompletionItem, CompletionItemKind};
+/// Complete dot accesses, i.e. fields or methods (currently only fields).
+pub(super) fn complete_dot(acc: &mut Completions, ctx: &CompletionContext) -> Cancelable<()> {
+    let (function, receiver) = match (&ctx.function, ctx.dot_receiver) {
+        (Some(function), Some(receiver)) => (function, receiver),
+        _ => return Ok(()),
+    };
+    let infer_result = function.infer(ctx.db)?;
+    let syntax_mapping = function.body_syntax_mapping(ctx.db)?;
+    let expr = match syntax_mapping.node_expr(receiver) {
+        Some(expr) => expr,
+        None => return Ok(()),
+    };
+    let receiver_ty = infer_result[expr].clone();
+    if !ctx.is_method_call {
+        complete_fields(acc, ctx, receiver_ty)?;
+    }
+    Ok(())
+}
+fn complete_fields(acc: &mut Completions, ctx: &CompletionContext, receiver: Ty) -> Cancelable<()> {
+    for receiver in receiver.autoderef(ctx.db) {
+        match receiver {
+            Ty::Adt { def_id, .. } => {
+                match def_id.resolve(ctx.db)? {
+                    Def::Struct(s) => {
+                        let variant_data = s.variant_data(ctx.db)?;
+                        for field in variant_data.fields() {
+                            CompletionItem::new(
+                                CompletionKind::Reference,
+                                field.name().to_string(),
+                            )
+                            .kind(CompletionItemKind::Field)
+                            .add_to(acc);
+                        }
+                    }
+                    // TODO unions
+                    _ => {}
+                }
+            }
+            Ty::Tuple(fields) => {
+                for (i, _ty) in fields.iter().enumerate() {
+                    CompletionItem::new(CompletionKind::Reference, i.to_string())
+                        .kind(CompletionItemKind::Field)
+                        .add_to(acc);
+                }
+            }
+            _ => {}
+        };
+    }
+    Ok(())
+}
+#[cfg(test)]
+mod tests {
+    use crate::completion::*;
+    fn check_ref_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Reference);
+    }
+    #[test]
+    fn test_struct_field_completion() {
+        check_ref_completion(
+            r"
+            struct A { the_field: u32 }
+            fn foo(a: A) {
+               a.<|>
+            }
+            ",
+            r#"the_field"#,
+        );
+    }
+    #[test]
+    fn test_struct_field_completion_self() {
+        check_ref_completion(
+            r"
+            struct A { the_field: u32 }
+            impl A {
+                fn foo(self) {
+                    self.<|>
+                }
+            }
+            ",
+            r#"the_field"#,
+        );
+    }
+    #[test]
+    fn test_struct_field_completion_autoderef() {
+        check_ref_completion(
+            r"
+            struct A { the_field: u32 }
+            impl A {
+                fn foo(&self) {
+                    self.<|>
+                }
+            }
+            ",
+            r#"the_field"#,
+        );
+    }
+    #[test]
+    fn test_no_struct_field_completion_for_method_call() {
+        check_ref_completion(
+            r"
+            struct A { the_field: u32 }
+            fn foo(a: A) {
+               a.<|>()
+            }
+            ",
+            r#""#,
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/complete_fn_param.rs b/crates/ra_ide_api/src/completion/complete_fn_param.rs
new file mode 100644
index 000000000..c1739e47e
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_fn_param.rs
@@ -0,0 +1,102 @@
+use ra_syntax::{
+    algo::visit::{visitor_ctx, VisitorCtx},
+    ast,
+    AstNode,
+};
+use rustc_hash::FxHashMap;
+use crate::completion::{CompletionContext, Completions, CompletionKind, CompletionItem};
+/// Complete repeated parametes, both name and type. For example, if all
+/// functions in a file have a `spam: &mut Spam` parameter, a completion with
+/// `spam: &mut Spam` insert text/label and `spam` lookup string will be
+/// suggested.
+pub(super) fn complete_fn_param(acc: &mut Completions, ctx: &CompletionContext) {
+    if !ctx.is_param {
+        return;
+    }
+    let mut params = FxHashMap::default();
+    for node in ctx.leaf.ancestors() {
+        let _ = visitor_ctx(&mut params)
+            .visit::<ast::SourceFile, _>(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)| {
+            CompletionItem::new(CompletionKind::Magic, label)
+                .lookup_by(lookup)
+                .add_to(acc)
+        });
+    fn process<'a, N: ast::FnDefOwner>(
+        node: &'a N,
+        params: &mut FxHashMap<String, (u32, &'a ast::Param)>,
+    ) {
+        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;
+            })
+    }
+}
+#[cfg(test)]
+mod tests {
+    use crate::completion::*;
+    fn check_magic_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Magic);
+    }
+    #[test]
+    fn test_param_completion_last_param() {
+        check_magic_completion(
+            r"
+            fn foo(file_id: FileId) {}
+            fn bar(file_id: FileId) {}
+            fn baz(file<|>) {}
+            ",
+            r#"file_id "file_id: FileId""#,
+        );
+    }
+    #[test]
+    fn test_param_completion_nth_param() {
+        check_magic_completion(
+            r"
+            fn foo(file_id: FileId) {}
+            fn bar(file_id: FileId) {}
+            fn baz(file<|>, x: i32) {}
+            ",
+            r#"file_id "file_id: FileId""#,
+        );
+    }
+    #[test]
+    fn test_param_completion_trait_param() {
+        check_magic_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#"file_id "file_id: FileId""#,
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/complete_keyword.rs b/crates/ra_ide_api/src/completion/complete_keyword.rs
new file mode 100644
index 000000000..d350f06ce
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_keyword.rs
@@ -0,0 +1,339 @@
+use ra_syntax::{
+    algo::visit::{visitor, Visitor},
+    AstNode,
+    ast::{self, LoopBodyOwner},
+    SyntaxKind::*, SyntaxNode,
+};
+use crate::completion::{CompletionContext, CompletionItem, Completions, CompletionKind, CompletionItemKind};
+pub(super) fn complete_use_tree_keyword(acc: &mut Completions, ctx: &CompletionContext) {
+    // complete keyword "crate" in use stmt
+    match (ctx.use_item_syntax.as_ref(), ctx.path_prefix.as_ref()) {
+        (Some(_), None) => {
+            CompletionItem::new(CompletionKind::Keyword, "crate")
+                .kind(CompletionItemKind::Keyword)
+                .lookup_by("crate")
+                .snippet("crate::")
+                .add_to(acc);
+            CompletionItem::new(CompletionKind::Keyword, "self")
+                .kind(CompletionItemKind::Keyword)
+                .lookup_by("self")
+                .add_to(acc);
+            CompletionItem::new(CompletionKind::Keyword, "super")
+                .kind(CompletionItemKind::Keyword)
+                .lookup_by("super")
+                .add_to(acc);
+        }
+        (Some(_), Some(_)) => {
+            CompletionItem::new(CompletionKind::Keyword, "self")
+                .kind(CompletionItemKind::Keyword)
+                .lookup_by("self")
+                .add_to(acc);
+            CompletionItem::new(CompletionKind::Keyword, "super")
+                .kind(CompletionItemKind::Keyword)
+                .lookup_by("super")
+                .add_to(acc);
+        }
+        _ => {}
+    }
+}
+fn keyword(kw: &str, snippet: &str) -> CompletionItem {
+    CompletionItem::new(CompletionKind::Keyword, kw)
+        .kind(CompletionItemKind::Keyword)
+        .snippet(snippet)
+        .build()
+}
+pub(super) fn complete_expr_keyword(acc: &mut Completions, ctx: &CompletionContext) {
+    if !ctx.is_trivial_path {
+        return;
+    }
+    let fn_def = match ctx.function_syntax {
+        Some(it) => it,
+        None => return,
+    };
+    acc.add(keyword("if", "if $0 {}"));
+    acc.add(keyword("match", "match $0 {}"));
+    acc.add(keyword("while", "while $0 {}"));
+    acc.add(keyword("loop", "loop {$0}"));
+    if ctx.after_if {
+        acc.add(keyword("else", "else {$0}"));
+        acc.add(keyword("else if", "else if $0 {}"));
+    }
+    if is_in_loop_body(ctx.leaf) {
+        if ctx.can_be_stmt {
+            acc.add(keyword("continue", "continue;"));
+            acc.add(keyword("break", "break;"));
+        } else {
+            acc.add(keyword("continue", "continue"));
+            acc.add(keyword("break", "break"));
+        }
+    }
+    acc.add_all(complete_return(fn_def, ctx.can_be_stmt));
+}
+fn is_in_loop_body(leaf: &SyntaxNode) -> bool {
+    for node in leaf.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 leaf.range().is_subrange(&body.syntax().range()) {
+                return true;
+            }
+        }
+    }
+    false
+}
+fn complete_return(fn_def: &ast::FnDef, can_be_stmt: bool) -> Option<CompletionItem> {
+    let snip = match (can_be_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))
+}
+#[cfg(test)]
+mod tests {
+    use crate::completion::{CompletionKind, check_completion};
+    fn check_keyword_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Keyword);
+    }
+    #[test]
+    fn completes_keywords_in_use_stmt() {
+        check_keyword_completion(
+            r"
+            use <|>
+            ",
+            r#"
+            crate "crate" "crate::"
+            self "self"
+            super "super"
+            "#,
+        );
+        check_keyword_completion(
+            r"
+            use a::<|>
+            ",
+            r#"
+            self "self"
+            super "super"
+            "#,
+        );
+        check_keyword_completion(
+            r"
+            use a::{b, <|>}
+            ",
+            r#"
+            self "self"
+            super "super"
+            "#,
+        );
+    }
+    #[test]
+    fn completes_various_keywords_in_function() {
+        check_keyword_completion(
+            r"
+            fn quux() {
+                <|>
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return;"
+            "#,
+        );
+    }
+    #[test]
+    fn completes_else_after_if() {
+        check_keyword_completion(
+            r"
+            fn quux() {
+                if true {
+                    ()
+                } <|>
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            else "else {$0}"
+            else if "else if $0 {}"
+            return "return;"
+            "#,
+        );
+    }
+    #[test]
+    fn test_completion_return_value() {
+        check_keyword_completion(
+            r"
+            fn quux() -> i32 {
+                <|>
+                92
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return $0;"
+            "#,
+        );
+        check_keyword_completion(
+            r"
+            fn quux() {
+                <|>
+                92
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return;"
+            "#,
+        );
+    }
+    #[test]
+    fn dont_add_semi_after_return_if_not_a_statement() {
+        check_keyword_completion(
+            r"
+            fn quux() -> i32 {
+                match () {
+                    () => <|>
+                }
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return $0"
+            "#,
+        );
+    }
+    #[test]
+    fn last_return_in_block_has_semi() {
+        check_keyword_completion(
+            r"
+            fn quux() -> i32 {
+                if condition {
+                    <|>
+                }
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return $0;"
+            "#,
+        );
+        check_keyword_completion(
+            r"
+            fn quux() -> i32 {
+                if condition {
+                    <|>
+                }
+                let x = 92;
+                x
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return $0;"
+            "#,
+        );
+    }
+    #[test]
+    fn completes_break_and_continue_in_loops() {
+        check_keyword_completion(
+            r"
+            fn quux() -> i32 {
+                loop { <|> }
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            continue "continue;"
+            break "break;"
+            return "return $0;"
+            "#,
+        );
+        // No completion: lambda isolates control flow
+        check_keyword_completion(
+            r"
+            fn quux() -> i32 {
+                loop { || { <|> } }
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            return "return $0;"
+            "#,
+        );
+    }
+    #[test]
+    fn no_semi_after_break_continue_in_expr() {
+        check_keyword_completion(
+            r"
+            fn f() {
+                loop {
+                    match () {
+                        () => br<|>
+                    }
+                }
+            }
+            ",
+            r#"
+            if "if $0 {}"
+            match "match $0 {}"
+            while "while $0 {}"
+            loop "loop {$0}"
+            continue "continue"
+            break "break"
+            return "return"
+            "#,
+        )
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/complete_path.rs b/crates/ra_ide_api/src/completion/complete_path.rs
new file mode 100644
index 000000000..4723a65a6
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_path.rs
@@ -0,0 +1,128 @@
+use crate::{
+    Cancelable,
+    completion::{CompletionItem, CompletionItemKind, Completions, CompletionKind, CompletionContext},
+};
+pub(super) fn complete_path(acc: &mut Completions, ctx: &CompletionContext) -> Cancelable<()> {
+    let (path, module) = match (&ctx.path_prefix, &ctx.module) {
+        (Some(path), Some(module)) => (path.clone(), module),
+        _ => return Ok(()),
+    };
+    let def_id = match module.resolve_path(ctx.db, &path)?.take_types() {
+        Some(it) => it,
+        None => return Ok(()),
+    };
+    match def_id.resolve(ctx.db)? {
+        hir::Def::Module(module) => {
+            let module_scope = module.scope(ctx.db)?;
+            module_scope.entries().for_each(|(name, res)| {
+                CompletionItem::new(CompletionKind::Reference, name.to_string())
+                    .from_resolution(ctx, res)
+                    .add_to(acc)
+            });
+        }
+        hir::Def::Enum(e) => e
+            .variants(ctx.db)?
+            .into_iter()
+            .for_each(|(name, _variant)| {
+                CompletionItem::new(CompletionKind::Reference, name.to_string())
+                    .kind(CompletionItemKind::EnumVariant)
+                    .add_to(acc)
+            }),
+        _ => return Ok(()),
+    };
+    Ok(())
+}
+#[cfg(test)]
+mod tests {
+    use crate::completion::{CompletionKind, check_completion};
+    fn check_reference_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Reference);
+    }
+    #[test]
+    fn completes_use_item_starting_with_self() {
+        check_reference_completion(
+            r"
+            use self::m::<|>;
+            mod m {
+                struct Bar;
+            }
+            ",
+            "Bar",
+        );
+    }
+    #[test]
+    fn completes_use_item_starting_with_crate() {
+        check_reference_completion(
+            "
+            //- /lib.rs
+            mod foo;
+            struct Spam;
+            //- /foo.rs
+            use crate::Sp<|>
+            ",
+            "Spam;foo",
+        );
+    }
+    #[test]
+    fn completes_nested_use_tree() {
+        check_reference_completion(
+            "
+            //- /lib.rs
+            mod foo;
+            struct Spam;
+            //- /foo.rs
+            use crate::{Sp<|>};
+            ",
+            "Spam;foo",
+        );
+    }
+    #[test]
+    fn completes_deeply_nested_use_tree() {
+        check_reference_completion(
+            "
+            //- /lib.rs
+            mod foo;
+            pub mod bar {
+                pub mod baz {
+                    pub struct Spam;
+                }
+            }
+            //- /foo.rs
+            use crate::{bar::{baz::Sp<|>}};
+            ",
+            "Spam",
+        );
+    }
+    #[test]
+    fn completes_enum_variant() {
+        check_reference_completion(
+            "
+            //- /lib.rs
+            enum E { Foo, Bar(i32) }
+            fn foo() { let _ = E::<|> }
+            ",
+            "Foo;Bar",
+        );
+    }
+    #[test]
+    fn dont_render_function_parens_in_use_item() {
+        check_reference_completion(
+            "
+            //- /lib.rs
+            mod m { pub fn foo() {} }
+            use crate::m::f<|>;
+            ",
+            "foo",
+        )
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/complete_scope.rs b/crates/ra_ide_api/src/completion/complete_scope.rs
new file mode 100644
index 000000000..ee9052d3d
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_scope.rs
@@ -0,0 +1,192 @@
+use rustc_hash::FxHashSet;
+use ra_syntax::TextUnit;
+use crate::{
+    Cancelable,
+    completion::{CompletionItem, CompletionItemKind, Completions, CompletionKind, CompletionContext},
+};
+pub(super) fn complete_scope(acc: &mut Completions, ctx: &CompletionContext) -> Cancelable<()> {
+    if !ctx.is_trivial_path {
+        return Ok(());
+    }
+    let module = match &ctx.module {
+        Some(it) => it,
+        None => return Ok(()),
+    };
+    if let Some(function) = &ctx.function {
+        let scopes = function.scopes(ctx.db)?;
+        complete_fn(acc, &scopes, ctx.offset);
+    }
+    let module_scope = module.scope(ctx.db)?;
+    let (file_id, _) = module.defenition_source(ctx.db)?;
+    module_scope
+        .entries()
+        .filter(|(_name, res)| {
+            // Don't expose this item
+            // FIXME: this penetrates through all kinds of abstractions,
+            // we need to figura out the way to do it less ugly.
+            match res.import {
+                None => true,
+                Some(import) => {
+                    let range = import.range(ctx.db, file_id);
+                    !range.is_subrange(&ctx.leaf.range())
+                }
+            }
+        })
+        .for_each(|(name, res)| {
+            CompletionItem::new(CompletionKind::Reference, name.to_string())
+                .from_resolution(ctx, res)
+                .add_to(acc)
+        });
+    Ok(())
+}
+fn complete_fn(acc: &mut Completions, scopes: &hir::ScopesWithSyntaxMapping, offset: TextUnit) {
+    let mut shadowed = FxHashSet::default();
+    scopes
+        .scope_chain_for_offset(offset)
+        .flat_map(|scope| scopes.scopes.entries(scope).iter())
+        .filter(|entry| shadowed.insert(entry.name()))
+        .for_each(|entry| {
+            CompletionItem::new(CompletionKind::Reference, entry.name().to_string())
+                .kind(CompletionItemKind::Binding)
+                .add_to(acc)
+        });
+}
+#[cfg(test)]
+mod tests {
+    use crate::completion::{CompletionKind, check_completion};
+    fn check_reference_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Reference);
+    }
+    #[test]
+    fn completes_bindings_from_let() {
+        check_reference_completion(
+            r"
+            fn quux(x: i32) {
+                let y = 92;
+                1 + <|>;
+                let z = ();
+            }
+            ",
+            r#"y;x;quux "quux($0)""#,
+        );
+    }
+    #[test]
+    fn completes_bindings_from_if_let() {
+        check_reference_completion(
+            r"
+            fn quux() {
+                if let Some(x) = foo() {
+                    let y = 92;
+                };
+                if let Some(a) = bar() {
+                    let b = 62;
+                    1 + <|>
+                }
+            }
+            ",
+            r#"b;a;quux "quux()$0""#,
+        );
+    }
+    #[test]
+    fn completes_bindings_from_for() {
+        check_reference_completion(
+            r"
+            fn quux() {
+                for x in &[1, 2, 3] {
+                    <|>
+                }
+            }
+            ",
+            r#"x;quux "quux()$0""#,
+        );
+    }
+    #[test]
+    fn completes_module_items() {
+        check_reference_completion(
+            r"
+            struct Foo;
+            enum Baz {}
+            fn quux() {
+                <|>
+            }
+            ",
+            r#"quux "quux()$0";Foo;Baz"#,
+        );
+    }
+    #[test]
+    fn completes_module_items_in_nested_modules() {
+        check_reference_completion(
+            r"
+            struct Foo;
+            mod m {
+                struct Bar;
+                fn quux() { <|> }
+            }
+            ",
+            r#"quux "quux()$0";Bar"#,
+        );
+    }
+    #[test]
+    fn completes_return_type() {
+        check_reference_completion(
+            r"
+            struct Foo;
+            fn x() -> <|>
+            ",
+            r#"Foo;x "x()$0""#,
+        )
+    }
+    #[test]
+    fn dont_show_both_completions_for_shadowing() {
+        check_reference_completion(
+            r"
+            fn foo() -> {
+                let bar = 92;
+                {
+                    let bar = 62;
+                    <|>
+                }
+            }
+            ",
+            r#"bar;foo "foo()$0""#,
+        )
+    }
+    #[test]
+    fn completes_self_in_methods() {
+        check_reference_completion(r"impl S { fn foo(&self) { <|> } }", "self")
+    }
+    #[test]
+    fn inserts_parens_for_function_calls() {
+        check_reference_completion(
+            r"
+            fn no_args() {}
+            fn main() { no_<|> }
+            ",
+            r#"no_args "no_args()$0"
+               main "main()$0""#,
+        );
+        check_reference_completion(
+            r"
+            fn with_args(x: i32, y: String) {}
+            fn main() { with_<|> }
+            ",
+            r#"main "main()$0"
+               with_args "with_args($0)""#,
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/complete_snippet.rs b/crates/ra_ide_api/src/completion/complete_snippet.rs
new file mode 100644
index 000000000..a495751dd
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_snippet.rs
@@ -0,0 +1,73 @@
+use crate::completion::{CompletionItem, Completions, CompletionKind, CompletionItemKind, CompletionContext, completion_item::Builder};
+fn snippet(label: &str, snippet: &str) -> Builder {
+    CompletionItem::new(CompletionKind::Snippet, label)
+        .snippet(snippet)
+        .kind(CompletionItemKind::Snippet)
+}
+pub(super) fn complete_expr_snippet(acc: &mut Completions, ctx: &CompletionContext) {
+    if !(ctx.is_trivial_path && ctx.function_syntax.is_some()) {
+        return;
+    }
+    snippet("pd", "eprintln!(\"$0 = {:?}\", $0);").add_to(acc);
+    snippet("ppd", "eprintln!(\"$0 = {:#?}\", $0);").add_to(acc);
+}
+pub(super) fn complete_item_snippet(acc: &mut Completions, ctx: &CompletionContext) {
+    if !ctx.is_new_item {
+        return;
+    }
+    snippet(
+        "Test function",
+        "\
+#[test]
+fn ${1:feature}() {
+    $0
+}",
+    )
+    .lookup_by("tfn")
+    .add_to(acc);
+    snippet("pub(crate)", "pub(crate) $0").add_to(acc);
+}
+#[cfg(test)]
+mod tests {
+    use crate::completion::{CompletionKind, check_completion};
+    fn check_snippet_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Snippet);
+    }
+    #[test]
+    fn completes_snippets_in_expressions() {
+        check_snippet_completion(
+            r"fn foo(x: i32) { <|> }",
+            r##"
+            pd "eprintln!(\"$0 = {:?}\", $0);"
+            ppd "eprintln!(\"$0 = {:#?}\", $0);"
+            "##,
+        );
+    }
+    #[test]
+    fn completes_snippets_in_items() {
+        // check_snippet_completion(r"
+        //     <|>
+        //     ",
+        //     r##"[CompletionItem { label: "Test function", lookup: None, snippet: Some("#[test]\nfn test_${1:feature}() {\n$0\n}"##,
+        // );
+        check_snippet_completion(
+            r"
+            #[cfg(test)]
+            mod tests {
+                <|>
+            }
+            ",
+            r##"
+            tfn "Test function" "#[test]\nfn ${1:feature}() {\n    $0\n}"
+            pub(crate) "pub(crate) $0"
+            "##,
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/completion_context.rs b/crates/ra_ide_api/src/completion/completion_context.rs
new file mode 100644
index 000000000..01786bb69
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/completion_context.rs
@@ -0,0 +1,205 @@
+use ra_text_edit::AtomTextEdit;
+use ra_syntax::{
+    AstNode, SyntaxNode, SourceFile, TextUnit, TextRange,
+    ast,
+    algo::{find_leaf_at_offset, find_covering_node, find_node_at_offset},
+    SyntaxKind::*,
+};
+use hir::source_binder;
+use crate::{db, FilePosition, Cancelable};
+/// `CompletionContext` is created early during completion to figure out, where
+/// exactly is the cursor, syntax-wise.
+#[derive(Debug)]
+pub(super) struct CompletionContext<'a> {
+    pub(super) db: &'a db::RootDatabase,
+    pub(super) offset: TextUnit,
+    pub(super) leaf: &'a SyntaxNode,
+    pub(super) module: Option<hir::Module>,
+    pub(super) function: Option<hir::Function>,
+    pub(super) function_syntax: Option<&'a ast::FnDef>,
+    pub(super) use_item_syntax: Option<&'a ast::UseItem>,
+    pub(super) is_param: bool,
+    /// A single-indent path, like `foo`.
+    pub(super) is_trivial_path: bool,
+    /// If not a trivial, path, the prefix (qualifier).
+    pub(super) path_prefix: Option<hir::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,
+    /// Something is typed at the "top" level, in module or impl/trait.
+    pub(super) is_new_item: bool,
+    /// The receiver if this is a field or method access, i.e. writing something.<|>
+    pub(super) dot_receiver: Option<&'a ast::Expr>,
+    /// If this is a method call in particular, i.e. the () are already there.
+    pub(super) is_method_call: bool,
+}
+impl<'a> CompletionContext<'a> {
+    pub(super) fn new(
+        db: &'a db::RootDatabase,
+        original_file: &'a SourceFile,
+        position: FilePosition,
+    ) -> Cancelable<Option<CompletionContext<'a>>> {
+        let module = source_binder::module_from_position(db, position)?;
+        let leaf =
+            ctry!(find_leaf_at_offset(original_file.syntax(), position.offset).left_biased());
+        let mut ctx = CompletionContext {
+            db,
+            leaf,
+            offset: position.offset,
+            module,
+            function: None,
+            function_syntax: None,
+            use_item_syntax: None,
+            is_param: false,
+            is_trivial_path: false,
+            path_prefix: None,
+            after_if: false,
+            can_be_stmt: false,
+            is_new_item: false,
+            dot_receiver: None,
+            is_method_call: false,
+        };
+        ctx.fill(original_file, position.offset);
+        Ok(Some(ctx))
+    }
+    fn fill(&mut self, original_file: &'a SourceFile, offset: TextUnit) {
+        // Insert a fake ident to get a valid parse tree. We will use this file
+        // to determine context, though the original_file will be used for
+        // actual completion.
+        let file = {
+            let edit = AtomTextEdit::insert(offset, "intellijRulezz".to_string());
+            original_file.reparse(&edit)
+        };
+        // First, let's try to complete a reference to some declaration.
+        if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(file.syntax(), 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;
+            }
+            self.classify_name_ref(original_file, name_ref);
+        }
+        // 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.syntax(), offset) {
+            if is_node::<ast::Param>(name.syntax()) {
+                self.is_param = true;
+                return;
+            }
+        }
+    }
+    fn classify_name_ref(&mut self, original_file: &'a SourceFile, name_ref: &ast::NameRef) {
+        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(SOURCE_FILE) | Some(ITEM_LIST) => {
+                self.is_new_item = true;
+                return;
+            }
+            _ => (),
+        }
+        self.use_item_syntax = self.leaf.ancestors().find_map(ast::UseItem::cast);
+        self.function_syntax = self
+            .leaf
+            .ancestors()
+            .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
+            .find_map(ast::FnDef::cast);
+        match (&self.module, self.function_syntax) {
+            (Some(module), Some(fn_def)) => {
+                let function = source_binder::function_from_module(self.db, module, fn_def);
+                self.function = Some(function);
+            }
+            _ => (),
+        }
+        let parent = match name_ref.syntax().parent() {
+            Some(it) => it,
+            None => return,
+        };
+        if let Some(segment) = ast::PathSegment::cast(parent) {
+            let path = segment.parent_path();
+            if let Some(mut path) = hir::Path::from_ast(path) {
+                if !path.is_ident() {
+                    path.segments.pop().unwrap();
+                    self.path_prefix = Some(path);
+                    return;
+                }
+            }
+            if path.qualifier().is_none() {
+                self.is_trivial_path = true;
+                // Find either enclosing expr statement (thing with `;`) or a
+                // block. If block, check that we are the last expr.
+                self.can_be_stmt = name_ref
+                    .syntax()
+                    .ancestors()
+                    .find_map(|node| {
+                        if let Some(stmt) = ast::ExprStmt::cast(node) {
+                            return Some(stmt.syntax().range() == name_ref.syntax().range());
+                        }
+                        if let Some(block) = ast::Block::cast(node) {
+                            return Some(
+                                block.expr().map(|e| e.syntax().range())
+                                    == Some(name_ref.syntax().range()),
+                            );
+                        }
+                        None
+                    })
+                    .unwrap_or(false);
+                if let Some(off) = name_ref.syntax().range().start().checked_sub(2.into()) {
+                    if let Some(if_expr) =
+                        find_node_at_offset::<ast::IfExpr>(original_file.syntax(), off)
+                    {
+                        if if_expr.syntax().range().end() < name_ref.syntax().range().start() {
+                            self.after_if = true;
+                        }
+                    }
+                }
+            }
+        }
+        if let Some(field_expr) = ast::FieldExpr::cast(parent) {
+            // The receiver comes before the point of insertion of the fake
+            // ident, so it should have the same range in the non-modified file
+            self.dot_receiver = field_expr
+                .expr()
+                .map(|e| e.syntax().range())
+                .and_then(|r| find_node_with_range(original_file.syntax(), r));
+        }
+        if let Some(method_call_expr) = ast::MethodCallExpr::cast(parent) {
+            // As above
+            self.dot_receiver = method_call_expr
+                .expr()
+                .map(|e| e.syntax().range())
+                .and_then(|r| find_node_with_range(original_file.syntax(), r));
+            self.is_method_call = true;
+        }
+    }
+}
+fn find_node_with_range<N: AstNode>(syntax: &SyntaxNode, range: TextRange) -> Option<&N> {
+    let node = find_covering_node(syntax, range);
+    node.ancestors().find_map(N::cast)
+}
+fn is_node<N: AstNode>(node: &SyntaxNode) -> bool {
+    match node.ancestors().filter_map(N::cast).next() {
+        None => false,
+        Some(n) => n.syntax().range() == node.range(),
+    }
+}
diff --git a/crates/ra_ide_api/src/completion/completion_item.rs b/crates/ra_ide_api/src/completion/completion_item.rs
new file mode 100644
index 000000000..a25b87bee
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/completion_item.rs
@@ -0,0 +1,244 @@
+use hir::PerNs;
+use crate::completion::CompletionContext;
+/// `CompletionItem` describes a single completion variant in the editor pop-up.
+/// It is basically a POD with various properties. To construct a
+/// `CompletionItem`, use `new` method and the `Builder` struct.
+#[derive(Debug)]
+pub struct CompletionItem {
+    /// Used only internally in tests, to check only specific kind of
+    /// completion.
+    completion_kind: CompletionKind,
+    label: String,
+    lookup: Option<String>,
+    snippet: Option<String>,
+    kind: Option<CompletionItemKind>,
+}
+pub enum InsertText {
+    PlainText { text: String },
+    Snippet { text: String },
+}
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CompletionItemKind {
+    Snippet,
+    Keyword,
+    Module,
+    Function,
+    Struct,
+    Enum,
+    EnumVariant,
+    Binding,
+    Field,
+}
+#[derive(Debug, PartialEq, Eq)]
+pub(crate) enum CompletionKind {
+    /// Parser-based keyword completion.
+    Keyword,
+    /// Your usual "complete all valid identifiers".
+    Reference,
+    /// "Secret sauce" completions.
+    Magic,
+    Snippet,
+}
+impl CompletionItem {
+    pub(crate) fn new(completion_kind: CompletionKind, label: impl Into<String>) -> Builder {
+        let label = label.into();
+        Builder {
+            completion_kind,
+            label,
+            lookup: None,
+            snippet: None,
+            kind: None,
+        }
+    }
+    /// What user sees in pop-up in the UI.
+    pub fn label(&self) -> &str {
+        &self.label
+    }
+    /// What string is used for filtering.
+    pub fn lookup(&self) -> &str {
+        self.lookup
+            .as_ref()
+            .map(|it| it.as_str())
+            .unwrap_or(self.label())
+    }
+    /// What is inserted.
+    pub fn insert_text(&self) -> InsertText {
+        match &self.snippet {
+            None => InsertText::PlainText {
+                text: self.label.clone(),
+            },
+            Some(it) => InsertText::Snippet { text: it.clone() },
+        }
+    }
+    pub fn kind(&self) -> Option<CompletionItemKind> {
+        self.kind
+    }
+}
+/// A helper to make `CompletionItem`s.
+#[must_use]
+pub(crate) struct Builder {
+    completion_kind: CompletionKind,
+    label: String,
+    lookup: Option<String>,
+    snippet: Option<String>,
+    kind: Option<CompletionItemKind>,
+}
+impl Builder {
+    pub(crate) fn add_to(self, acc: &mut Completions) {
+        acc.add(self.build())
+    }
+    pub(crate) fn build(self) -> CompletionItem {
+        CompletionItem {
+            label: self.label,
+            lookup: self.lookup,
+            snippet: self.snippet,
+            kind: self.kind,
+            completion_kind: self.completion_kind,
+        }
+    }
+    pub(crate) fn lookup_by(mut self, lookup: impl Into<String>) -> Builder {
+        self.lookup = Some(lookup.into());
+        self
+    }
+    pub(crate) fn snippet(mut self, snippet: impl Into<String>) -> Builder {
+        self.snippet = Some(snippet.into());
+        self
+    }
+    pub(crate) fn kind(mut self, kind: CompletionItemKind) -> Builder {
+        self.kind = Some(kind);
+        self
+    }
+    pub(super) fn from_resolution(
+        mut self,
+        ctx: &CompletionContext,
+        resolution: &hir::Resolution,
+    ) -> Builder {
+        let resolved = resolution.def_id.and_then(|d| d.resolve(ctx.db).ok());
+        let kind = match resolved {
+            PerNs {
+                types: Some(hir::Def::Module(..)),
+                ..
+            } => CompletionItemKind::Module,
+            PerNs {
+                types: Some(hir::Def::Struct(..)),
+                ..
+            } => CompletionItemKind::Struct,
+            PerNs {
+                types: Some(hir::Def::Enum(..)),
+                ..
+            } => CompletionItemKind::Enum,
+            PerNs {
+                values: Some(hir::Def::Function(function)),
+                ..
+            } => return self.from_function(ctx, function),
+            _ => return self,
+        };
+        self.kind = Some(kind);
+        self
+    }
+    fn from_function(mut self, ctx: &CompletionContext, function: hir::Function) -> Builder {
+        // If not an import, add parenthesis automatically.
+        if ctx.use_item_syntax.is_none() {
+            if function.signature(ctx.db).args().is_empty() {
+                self.snippet = Some(format!("{}()$0", self.label));
+            } else {
+                self.snippet = Some(format!("{}($0)", self.label));
+            }
+        }
+        self.kind = Some(CompletionItemKind::Function);
+        self
+    }
+}
+impl Into<CompletionItem> for Builder {
+    fn into(self) -> CompletionItem {
+        self.build()
+    }
+}
+/// Represents an in-progress set of completions being built.
+#[derive(Debug, Default)]
+pub(crate) struct Completions {
+    buf: Vec<CompletionItem>,
+}
+impl Completions {
+    pub(crate) fn add(&mut self, item: impl Into<CompletionItem>) {
+        self.buf.push(item.into())
+    }
+    pub(crate) fn add_all<I>(&mut self, items: I)
+    where
+        I: IntoIterator,
+        I::Item: Into<CompletionItem>,
+    {
+        items.into_iter().for_each(|item| self.add(item.into()))
+    }
+    #[cfg(test)]
+    pub(crate) fn assert_match(&self, expected: &str, kind: CompletionKind) {
+        let expected = normalize(expected);
+        let actual = self.debug_render(kind);
+        test_utils::assert_eq_text!(expected.as_str(), actual.as_str(),);
+        /// Normalize the textual representation of `Completions`:
+        /// replace `;` with newlines, normalize whitespace
+        fn normalize(expected: &str) -> String {
+            use ra_syntax::{tokenize, TextUnit, TextRange, SyntaxKind::SEMI};
+            let mut res = String::new();
+            for line in expected.trim().lines() {
+                let line = line.trim();
+                let mut start_offset: TextUnit = 0.into();
+                // Yep, we use rust tokenize in completion tests :-)
+                for token in tokenize(line) {
+                    let range = TextRange::offset_len(start_offset, token.len);
+                    start_offset += token.len;
+                    if token.kind == SEMI {
+                        res.push('\n');
+                    } else {
+                        res.push_str(&line[range]);
+                    }
+                }
+                res.push('\n');
+            }
+            res
+        }
+    }
+    #[cfg(test)]
+    fn debug_render(&self, kind: CompletionKind) -> String {
+        let mut res = String::new();
+        for c in self.buf.iter() {
+            if c.completion_kind == kind {
+                if let Some(lookup) = &c.lookup {
+                    res.push_str(lookup);
+                    res.push_str(&format!(" {:?}", c.label));
+                } else {
+                    res.push_str(&c.label);
+                }
+                if let Some(snippet) = &c.snippet {
+                    res.push_str(&format!(" {:?}", snippet));
+                }
+                res.push('\n');
+            }
+        }
+        res
+    }
+}
+impl Into<Vec<CompletionItem>> for Completions {
+    fn into(self) -> Vec<CompletionItem> {
+        self.buf
+    }
+}