1 files changed, 770 insertions, 0 deletions

diff --git a/crates/ide_assists/src/utils/suggest_name.rs b/crates/ide_assists/src/utils/suggest_name.rs
new file mode 100644
index 000000000..345e9af40
--- /dev/null
+++ b/crates/ide_assists/src/utils/suggest_name.rs
@@ -0,0 +1,770 @@
+//! This module contains functions to suggest names for expressions, functions and other items
+
+use hir::Semantics;
+use ide_db::RootDatabase;
+use itertools::Itertools;
+use stdx::to_lower_snake_case;
+use syntax::{
+    ast::{self, NameOwner},
+    match_ast, AstNode,
+};
+
+/// Trait names, that will be ignored when in `impl Trait` and `dyn Trait`
+const USELESS_TRAITS: &[&str] = &["Send", "Sync", "Copy", "Clone", "Eq", "PartialEq"];
+/// Identifier names that won't be suggested, ever
+///
+/// **NOTE**: they all must be snake lower case
+const USELESS_NAMES: &[&str] =
+    &["new", "default", "option", "some", "none", "ok", "err", "str", "string"];
+/// Generic types replaced by their first argument
+///
+/// # Examples
+/// `Option<Name>` -> `Name`
+/// `Result<User, Error>` -> `User`
+const WRAPPER_TYPES: &[&str] = &["Box", "Option", "Result"];
+/// Prefixes to strip from methods names
+///
+/// # Examples
+/// `vec.as_slice()` -> `slice`
+/// `args.into_config()` -> `config`
+/// `bytes.to_vec()` -> `vec`
+const USELESS_METHOD_PREFIXES: &[&str] = &["into_", "as_", "to_"];
+
+/// Suggest name of variable for given expression
+///
+/// **NOTE**: it is caller's responsibility to guarantee uniqueness of the name.
+/// I.e. it doesn't look for names in scope.
+///
+/// # Current implementation
+///
+/// In current implementation, the function tries to get the name from
+/// the following sources:
+///
+/// * if expr is an argument to function/method, use paramter name
+/// * if expr is a function/method call, use function name
+/// * expression type name if it exists (E.g. `()`, `fn() -> ()` or `!` do not have names)
+/// * fallback: `var_name`
+///
+/// It also applies heuristics to filter out less informative names
+///
+/// Currently it sticks to the first name found.
+pub(crate) fn variable(expr: &ast::Expr, sema: &Semantics<'_, RootDatabase>) -> String {
+    from_param(expr, sema)
+        .or_else(|| from_call(expr))
+        .or_else(|| from_type(expr, sema))
+        .unwrap_or_else(|| "var_name".to_string())
+}
+
+fn normalize(name: &str) -> Option<String> {
+    let name = to_lower_snake_case(name);
+
+    if USELESS_NAMES.contains(&name.as_str()) {
+        return None;
+    }
+
+    if !is_valid_name(&name) {
+        return None;
+    }
+
+    Some(name)
+}
+
+fn is_valid_name(name: &str) -> bool {
+    match syntax::lex_single_syntax_kind(name) {
+        Some((syntax::SyntaxKind::IDENT, _error)) => true,
+        _ => false,
+    }
+}
+
+fn from_call(expr: &ast::Expr) -> Option<String> {
+    from_func_call(expr).or_else(|| from_method_call(expr))
+}
+
+fn from_func_call(expr: &ast::Expr) -> Option<String> {
+    let call = match expr {
+        ast::Expr::CallExpr(call) => call,
+        _ => return None,
+    };
+    let func = match call.expr()? {
+        ast::Expr::PathExpr(path) => path,
+        _ => return None,
+    };
+    let ident = func.path()?.segment()?.name_ref()?.ident_token()?;
+    normalize(ident.text())
+}
+
+fn from_method_call(expr: &ast::Expr) -> Option<String> {
+    let method = match expr {
+        ast::Expr::MethodCallExpr(call) => call,
+        _ => return None,
+    };
+    let ident = method.name_ref()?.ident_token()?;
+    let name = normalize(ident.text())?;
+
+    for prefix in USELESS_METHOD_PREFIXES {
+        if let Some(suffix) = name.strip_prefix(prefix) {
+            return Some(suffix.to_string());
+        }
+    }
+
+    Some(name)
+}
+
+fn from_param(expr: &ast::Expr, sema: &Semantics<'_, RootDatabase>) -> Option<String> {
+    let arg_list = expr.syntax().parent().and_then(ast::ArgList::cast)?;
+    let args_parent = arg_list.syntax().parent()?;
+    let func = match_ast! {
+        match args_parent {
+            ast::CallExpr(call) => {
+                let func = call.expr()?;
+                let func_ty = sema.type_of_expr(&func)?;
+                func_ty.as_callable(sema.db)?
+            },
+            ast::MethodCallExpr(method) => sema.resolve_method_call_as_callable(&method)?,
+            _ => return None,
+        }
+    };
+
+    let (idx, _) = arg_list.args().find_position(|it| it == expr).unwrap();
+    let (pat, _) = func.params(sema.db).into_iter().nth(idx)?;
+    let pat = match pat? {
+        either::Either::Right(pat) => pat,
+        _ => return None,
+    };
+    let name = var_name_from_pat(&pat)?;
+    normalize(&name.to_string())
+}
+
+fn var_name_from_pat(pat: &ast::Pat) -> Option<ast::Name> {
+    match pat {
+        ast::Pat::IdentPat(var) => var.name(),
+        ast::Pat::RefPat(ref_pat) => var_name_from_pat(&ref_pat.pat()?),
+        ast::Pat::BoxPat(box_pat) => var_name_from_pat(&box_pat.pat()?),
+        _ => None,
+    }
+}
+
+fn from_type(expr: &ast::Expr, sema: &Semantics<'_, RootDatabase>) -> Option<String> {
+    let ty = sema.type_of_expr(expr)?;
+    let ty = ty.remove_ref().unwrap_or(ty);
+
+    name_of_type(&ty, sema.db)
+}
+
+fn name_of_type(ty: &hir::Type, db: &RootDatabase) -> Option<String> {
+    let name = if let Some(adt) = ty.as_adt() {
+        let name = adt.name(db).to_string();
+
+        if WRAPPER_TYPES.contains(&name.as_str()) {
+            let inner_ty = ty.type_parameters().next()?;
+            return name_of_type(&inner_ty, db);
+        }
+
+        name
+    } else if let Some(trait_) = ty.as_dyn_trait() {
+        trait_name(&trait_, db)?
+    } else if let Some(traits) = ty.as_impl_traits(db) {
+        let mut iter = traits.into_iter().filter_map(|t| trait_name(&t, db));
+        let name = iter.next()?;
+        if iter.next().is_some() {
+            return None;
+        }
+        name
+    } else {
+        return None;
+    };
+    normalize(&name)
+}
+
+fn trait_name(trait_: &hir::Trait, db: &RootDatabase) -> Option<String> {
+    let name = trait_.name(db).to_string();
+    if USELESS_TRAITS.contains(&name.as_str()) {
+        return None;
+    }
+    Some(name)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use crate::tests::check_name_suggestion;
+
+    mod from_func_call {
+        use super::*;
+
+        #[test]
+        fn no_args() {
+            check_name_suggestion(
+                |e, _| from_func_call(e),
+                r#"
+                fn foo() {
+                    $0bar()$0
+                }"#,
+                "bar",
+            );
+        }
+
+        #[test]
+        fn single_arg() {
+            check_name_suggestion(
+                |e, _| from_func_call(e),
+                r#"
+                fn foo() {
+                    $0bar(1)$0
+                }"#,
+                "bar",
+            );
+        }
+
+        #[test]
+        fn many_args() {
+            check_name_suggestion(
+                |e, _| from_func_call(e),
+                r#"
+                fn foo() {
+                    $0bar(1, 2, 3)$0
+                }"#,
+                "bar",
+            );
+        }
+
+        #[test]
+        fn path() {
+            check_name_suggestion(
+                |e, _| from_func_call(e),
+                r#"
+                fn foo() {
+                    $0i32::bar(1, 2, 3)$0
+                }"#,
+                "bar",
+            );
+        }
+
+        #[test]
+        fn generic_params() {
+            check_name_suggestion(
+                |e, _| from_func_call(e),
+                r#"
+                fn foo() {
+                    $0bar::<i32>(1, 2, 3)$0
+                }"#,
+                "bar",
+            );
+        }
+    }
+
+    mod from_method_call {
+        use super::*;
+
+        #[test]
+        fn no_args() {
+            check_name_suggestion(
+                |e, _| from_method_call(e),
+                r#"
+                fn foo() {
+                    $0bar.frobnicate()$0
+                }"#,
+                "frobnicate",
+            );
+        }
+
+        #[test]
+        fn generic_params() {
+            check_name_suggestion(
+                |e, _| from_method_call(e),
+                r#"
+                fn foo() {
+                    $0bar.frobnicate::<i32, u32>()$0
+                }"#,
+                "frobnicate",
+            );
+        }
+
+        #[test]
+        fn to_name() {
+            check_name_suggestion(
+                |e, _| from_method_call(e),
+                r#"
+                struct Args;
+                struct Config;
+                impl Args {
+                    fn to_config(&self) -> Config {}
+                }
+                fn foo() {
+                    $0Args.to_config()$0;
+                }"#,
+                "config",
+            );
+        }
+    }
+
+    mod from_param {
+        use crate::tests::check_name_suggestion_not_applicable;
+
+        use super::*;
+
+        #[test]
+        fn plain_func() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                fn bar(n: i32, m: u32);
+                fn foo() {
+                    bar($01$0, 2)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn mut_param() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                fn bar(mut n: i32, m: u32);
+                fn foo() {
+                    bar($01$0, 2)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn func_does_not_exist() {
+            check_name_suggestion_not_applicable(
+                from_param,
+                r#"
+                fn foo() {
+                    bar($01$0, 2)
+                }"#,
+            );
+        }
+
+        #[test]
+        fn unnamed_param() {
+            check_name_suggestion_not_applicable(
+                from_param,
+                r#"
+                fn bar(_: i32, m: u32);
+                fn foo() {
+                    bar($01$0, 2)
+                }"#,
+            );
+        }
+
+        #[test]
+        fn tuple_pat() {
+            check_name_suggestion_not_applicable(
+                from_param,
+                r#"
+                fn bar((n, k): (i32, i32), m: u32);
+                fn foo() {
+                    bar($0(1, 2)$0, 3)
+                }"#,
+            );
+        }
+
+        #[test]
+        fn ref_pat() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                fn bar(&n: &i32, m: u32);
+                fn foo() {
+                    bar($0&1$0, 3)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn box_pat() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                fn bar(box n: &i32, m: u32);
+                fn foo() {
+                    bar($01$0, 3)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn param_out_of_index() {
+            check_name_suggestion_not_applicable(
+                from_param,
+                r#"
+                fn bar(n: i32, m: u32);
+                fn foo() {
+                    bar(1, 2, $03$0)
+                }"#,
+            );
+        }
+
+        #[test]
+        fn generic_param_resolved() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                fn bar<T>(n: T, m: u32);
+                fn foo() {
+                    bar($01$0, 2)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn generic_param_unresolved() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                fn bar<T>(n: T, m: u32);
+                fn foo<T>(x: T) {
+                    bar($0x$0, 2)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn method() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                struct S;
+                impl S {
+                    fn bar(&self, n: i32, m: u32);
+                }
+                fn foo() {
+                    S.bar($01$0, 2)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn method_ufcs() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                struct S;
+                impl S {
+                    fn bar(&self, n: i32, m: u32);
+                }
+                fn foo() {
+                    S::bar(&S, $01$0, 2)
+                }"#,
+                "n",
+            );
+        }
+
+        #[test]
+        fn method_self() {
+            check_name_suggestion_not_applicable(
+                from_param,
+                r#"
+                struct S;
+                impl S {
+                    fn bar(&self, n: i32, m: u32);
+                }
+                fn foo() {
+                    S::bar($0&S$0, 1, 2)
+                }"#,
+            );
+        }
+
+        #[test]
+        fn method_self_named() {
+            check_name_suggestion(
+                from_param,
+                r#"
+                struct S;
+                impl S {
+                    fn bar(strukt: &Self, n: i32, m: u32);
+                }
+                fn foo() {
+                    S::bar($0&S$0, 1, 2)
+                }"#,
+                "strukt",
+            );
+        }
+    }
+
+    mod from_type {
+        use crate::tests::check_name_suggestion_not_applicable;
+
+        use super::*;
+
+        #[test]
+        fn i32() {
+            check_name_suggestion_not_applicable(
+                from_type,
+                r#"
+                fn foo() {
+                    let _: i32 = $01$0;
+                }"#,
+            );
+        }
+
+        #[test]
+        fn u64() {
+            check_name_suggestion_not_applicable(
+                from_type,
+                r#"
+                fn foo() {
+                    let _: u64 = $01$0;
+                }"#,
+            );
+        }
+
+        #[test]
+        fn bool() {
+            check_name_suggestion_not_applicable(
+                from_type,
+                r#"
+                fn foo() {
+                    let _: bool = $0true$0;
+                }"#,
+            );
+        }
+
+        #[test]
+        fn struct_unit() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                struct Seed;
+                fn foo() {
+                    let _ = $0Seed$0;
+                }"#,
+                "seed",
+            );
+        }
+
+        #[test]
+        fn struct_unit_to_snake() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                struct SeedState;
+                fn foo() {
+                    let _ = $0SeedState$0;
+                }"#,
+                "seed_state",
+            );
+        }
+
+        #[test]
+        fn struct_single_arg() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                struct Seed(u32);
+                fn foo() {
+                    let _ = $0Seed(0)$0;
+                }"#,
+                "seed",
+            );
+        }
+
+        #[test]
+        fn struct_with_fields() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                struct Seed { value: u32 }
+                fn foo() {
+                    let _ = $0Seed { value: 0 }$0;
+                }"#,
+                "seed",
+            );
+        }
+
+        #[test]
+        fn enum_() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                enum Kind { A, B }
+                fn foo() {
+                    let _ = $0Kind::A$0;
+                }"#,
+                "kind",
+            );
+        }
+
+        #[test]
+        fn enum_generic_resolved() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                enum Kind<T> { A(T), B }
+                fn foo() {
+                    let _ = $0Kind::A(1)$0;
+                }"#,
+                "kind",
+            );
+        }
+
+        #[test]
+        fn enum_generic_unresolved() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                enum Kind<T> { A(T), B }
+                fn foo<T>(x: T) {
+                    let _ = $0Kind::A(x)$0;
+                }"#,
+                "kind",
+            );
+        }
+
+        #[test]
+        fn dyn_trait() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                trait DynHandler {}
+                fn bar() -> dyn DynHandler {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "dyn_handler",
+            );
+        }
+
+        #[test]
+        fn impl_trait() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                trait StaticHandler {}
+                fn bar() -> impl StaticHandler {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "static_handler",
+            );
+        }
+
+        #[test]
+        fn impl_trait_plus_clone() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                trait StaticHandler {}
+                trait Clone {}
+                fn bar() -> impl StaticHandler + Clone {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "static_handler",
+            );
+        }
+
+        #[test]
+        fn impl_trait_plus_lifetime() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                trait StaticHandler {}
+                trait Clone {}
+                fn bar<'a>(&'a i32) -> impl StaticHandler + 'a {}
+                fn foo() {
+                    $0bar(&1)$0;
+                }"#,
+                "static_handler",
+            );
+        }
+
+        #[test]
+        fn impl_trait_plus_trait() {
+            check_name_suggestion_not_applicable(
+                from_type,
+                r#"
+                trait Handler {}
+                trait StaticHandler {}
+                fn bar() -> impl StaticHandler + Handler {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+            );
+        }
+
+        #[test]
+        fn ref_value() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                struct Seed;
+                fn bar() -> &Seed {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "seed",
+            );
+        }
+
+        #[test]
+        fn box_value() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                struct Box<T>(*const T);
+                struct Seed;
+                fn bar() -> Box<Seed> {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "seed",
+            );
+        }
+
+        #[test]
+        fn box_generic() {
+            check_name_suggestion_not_applicable(
+                from_type,
+                r#"
+                struct Box<T>(*const T);
+                fn bar<T>() -> Box<T> {}
+                fn foo<T>() {
+                    $0bar::<T>()$0;
+                }"#,
+            );
+        }
+
+        #[test]
+        fn option_value() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                enum Option<T> { Some(T) }
+                struct Seed;
+                fn bar() -> Option<Seed> {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "seed",
+            );
+        }
+
+        #[test]
+        fn result_value() {
+            check_name_suggestion(
+                from_type,
+                r#"
+                enum Result<T, E> { Ok(T), Err(E) }
+                struct Seed;
+                struct Error;
+                fn bar() -> Result<Seed, Error> {}
+                fn foo() {
+                    $0bar()$0;
+                }"#,
+                "seed",
+            );
+        }
+    }
+}