1 files changed, 364 insertions, 0 deletions

diff --git a/crates/ide/src/typing.rs b/crates/ide/src/typing.rs
new file mode 100644
index 000000000..899ce5f26
--- /dev/null
+++ b/crates/ide/src/typing.rs
@@ -0,0 +1,364 @@
+//! This module handles auto-magic editing actions applied together with users
+//! edits. For example, if the user typed
+//!
+//! ```text
+//!     foo
+//!         .bar()
+//!         .baz()
+//!     |   // <- cursor is here
+//! ```
+//!
+//! and types `.` next, we want to indent the dot.
+//!
+//! Language server executes such typing assists synchronously. That is, they
+//! block user's typing and should be pretty fast for this reason!
+
+mod on_enter;
+
+use base_db::{FilePosition, SourceDatabase};
+use ide_db::{source_change::SourceFileEdit, RootDatabase};
+use syntax::{
+    algo::find_node_at_offset,
+    ast::{self, edit::IndentLevel, AstToken},
+    AstNode, SourceFile,
+    SyntaxKind::{FIELD_EXPR, METHOD_CALL_EXPR},
+    TextRange, TextSize,
+};
+
+use text_edit::TextEdit;
+
+use crate::SourceChange;
+
+pub(crate) use on_enter::on_enter;
+
+pub(crate) const TRIGGER_CHARS: &str = ".=>";
+
+// Feature: On Typing Assists
+//
+// Some features trigger on typing certain characters:
+//
+// - typing `let =` tries to smartly add `;` if `=` is followed by an existing expression
+// - typing `.` in a chain method call auto-indents
+pub(crate) fn on_char_typed(
+    db: &RootDatabase,
+    position: FilePosition,
+    char_typed: char,
+) -> Option<SourceChange> {
+    assert!(TRIGGER_CHARS.contains(char_typed));
+    let file = &db.parse(position.file_id).tree();
+    assert_eq!(file.syntax().text().char_at(position.offset), Some(char_typed));
+    let edit = on_char_typed_inner(file, position.offset, char_typed)?;
+    Some(SourceFileEdit { file_id: position.file_id, edit }.into())
+}
+
+fn on_char_typed_inner(file: &SourceFile, offset: TextSize, char_typed: char) -> Option<TextEdit> {
+    assert!(TRIGGER_CHARS.contains(char_typed));
+    match char_typed {
+        '.' => on_dot_typed(file, offset),
+        '=' => on_eq_typed(file, offset),
+        '>' => on_arrow_typed(file, offset),
+        _ => unreachable!(),
+    }
+}
+
+/// Returns an edit which should be applied after `=` was typed. Primarily,
+/// this works when adding `let =`.
+// FIXME: use a snippet completion instead of this hack here.
+fn on_eq_typed(file: &SourceFile, offset: TextSize) -> Option<TextEdit> {
+    assert_eq!(file.syntax().text().char_at(offset), Some('='));
+    let let_stmt: ast::LetStmt = find_node_at_offset(file.syntax(), offset)?;
+    if let_stmt.semicolon_token().is_some() {
+        return None;
+    }
+    if let Some(expr) = let_stmt.initializer() {
+        let expr_range = expr.syntax().text_range();
+        if expr_range.contains(offset) && offset != expr_range.start() {
+            return None;
+        }
+        if file.syntax().text().slice(offset..expr_range.start()).contains_char('\n') {
+            return None;
+        }
+    } else {
+        return None;
+    }
+    let offset = let_stmt.syntax().text_range().end();
+    Some(TextEdit::insert(offset, ";".to_string()))
+}
+
+/// Returns an edit which should be applied when a dot ('.') is typed on a blank line, indenting the line appropriately.
+fn on_dot_typed(file: &SourceFile, offset: TextSize) -> Option<TextEdit> {
+    assert_eq!(file.syntax().text().char_at(offset), Some('.'));
+    let whitespace =
+        file.syntax().token_at_offset(offset).left_biased().and_then(ast::Whitespace::cast)?;
+
+    let current_indent = {
+        let text = whitespace.text();
+        let newline = text.rfind('\n')?;
+        &text[newline + 1..]
+    };
+    let current_indent_len = TextSize::of(current_indent);
+
+    let parent = whitespace.syntax().parent();
+    // Make sure dot is a part of call chain
+    if !matches!(parent.kind(), FIELD_EXPR | METHOD_CALL_EXPR) {
+        return None;
+    }
+    let prev_indent = IndentLevel::from_node(&parent);
+    let target_indent = format!("    {}", prev_indent);
+    let target_indent_len = TextSize::of(&target_indent);
+    if current_indent_len == target_indent_len {
+        return None;
+    }
+
+    Some(TextEdit::replace(TextRange::new(offset - current_indent_len, offset), target_indent))
+}
+
+/// Adds a space after an arrow when `fn foo() { ... }` is turned into `fn foo() -> { ... }`
+fn on_arrow_typed(file: &SourceFile, offset: TextSize) -> Option<TextEdit> {
+    let file_text = file.syntax().text();
+    assert_eq!(file_text.char_at(offset), Some('>'));
+    let after_arrow = offset + TextSize::of('>');
+    if file_text.char_at(after_arrow) != Some('{') {
+        return None;
+    }
+    if find_node_at_offset::<ast::RetType>(file.syntax(), offset).is_none() {
+        return None;
+    }
+
+    Some(TextEdit::insert(after_arrow, " ".to_string()))
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::{assert_eq_text, extract_offset};
+
+    use super::*;
+
+    fn do_type_char(char_typed: char, before: &str) -> Option<String> {
+        let (offset, before) = extract_offset(before);
+        let edit = TextEdit::insert(offset, char_typed.to_string());
+        let mut before = before.to_string();
+        edit.apply(&mut before);
+        let parse = SourceFile::parse(&before);
+        on_char_typed_inner(&parse.tree(), offset, char_typed).map(|it| {
+            it.apply(&mut before);
+            before.to_string()
+        })
+    }
+
+    fn type_char(char_typed: char, ra_fixture_before: &str, ra_fixture_after: &str) {
+        let actual = do_type_char(char_typed, ra_fixture_before)
+            .unwrap_or_else(|| panic!("typing `{}` did nothing", char_typed));
+
+        assert_eq_text!(ra_fixture_after, &actual);
+    }
+
+    fn type_char_noop(char_typed: char, before: &str) {
+        let file_change = do_type_char(char_typed, before);
+        assert!(file_change.is_none())
+    }
+
+    #[test]
+    fn test_on_eq_typed() {
+        //     do_check(r"
+        // fn foo() {
+        //     let foo =<|>
+        // }
+        // ", r"
+        // fn foo() {
+        //     let foo =;
+        // }
+        // ");
+        type_char(
+            '=',
+            r"
+fn foo() {
+    let foo <|> 1 + 1
+}
+",
+            r"
+fn foo() {
+    let foo = 1 + 1;
+}
+",
+        );
+        //     do_check(r"
+        // fn foo() {
+        //     let foo =<|>
+        //     let bar = 1;
+        // }
+        // ", r"
+        // fn foo() {
+        //     let foo =;
+        //     let bar = 1;
+        // }
+        // ");
+    }
+
+    #[test]
+    fn indents_new_chain_call() {
+        type_char(
+            '.',
+            r"
+            fn main() {
+                xs.foo()
+                <|>
+            }
+            ",
+            r"
+            fn main() {
+                xs.foo()
+                    .
+            }
+            ",
+        );
+        type_char_noop(
+            '.',
+            r"
+            fn main() {
+                xs.foo()
+                    <|>
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn indents_new_chain_call_with_semi() {
+        type_char(
+            '.',
+            r"
+            fn main() {
+                xs.foo()
+                <|>;
+            }
+            ",
+            r"
+            fn main() {
+                xs.foo()
+                    .;
+            }
+            ",
+        );
+        type_char_noop(
+            '.',
+            r"
+            fn main() {
+                xs.foo()
+                    <|>;
+            }
+            ",
+        )
+    }
+
+    #[test]
+    fn indents_new_chain_call_with_let() {
+        type_char(
+            '.',
+            r#"
+fn main() {
+    let _ = foo
+    <|>
+    bar()
+}
+"#,
+            r#"
+fn main() {
+    let _ = foo
+        .
+    bar()
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn indents_continued_chain_call() {
+        type_char(
+            '.',
+            r"
+            fn main() {
+                xs.foo()
+                    .first()
+                <|>
+            }
+            ",
+            r"
+            fn main() {
+                xs.foo()
+                    .first()
+                    .
+            }
+            ",
+        );
+        type_char_noop(
+            '.',
+            r"
+            fn main() {
+                xs.foo()
+                    .first()
+                    <|>
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn indents_middle_of_chain_call() {
+        type_char(
+            '.',
+            r"
+            fn source_impl() {
+                let var = enum_defvariant_list().unwrap()
+                <|>
+                    .nth(92)
+                    .unwrap();
+            }
+            ",
+            r"
+            fn source_impl() {
+                let var = enum_defvariant_list().unwrap()
+                    .
+                    .nth(92)
+                    .unwrap();
+            }
+            ",
+        );
+        type_char_noop(
+            '.',
+            r"
+            fn source_impl() {
+                let var = enum_defvariant_list().unwrap()
+                    <|>
+                    .nth(92)
+                    .unwrap();
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn dont_indent_freestanding_dot() {
+        type_char_noop(
+            '.',
+            r"
+            fn main() {
+                <|>
+            }
+            ",
+        );
+        type_char_noop(
+            '.',
+            r"
+            fn main() {
+            <|>
+            }
+            ",
+        );
+    }
+
+    #[test]
+    fn adds_space_after_return_type() {
+        type_char('>', "fn foo() -<|>{ 92 }", "fn foo() -> { 92 }")
+    }
+}