assist to convert if-let to match

3 files changed, 119 insertions, 1 deletions

diff --git a/crates/ra_editor/src/assists.rs b/crates/ra_editor/src/assists.rs
index a320caabf..f839f6a7a 100644
--- a/crates/ra_editor/src/assists.rs
+++ b/crates/ra_editor/src/assists.rs
@@ -9,12 +9,15 @@ mod add_impl;
 mod introduce_variable;
 mod change_visibility;
 mod split_import;
+mod replace_if_let_with_match;
 
 use ra_text_edit::{TextEdit, TextEditBuilder};
 use ra_syntax::{
     Direction, SyntaxNode, TextUnit, TextRange, SourceFile, AstNode,
     algo::{find_leaf_at_offset, find_covering_node, LeafAtOffset},
+    ast::{self, AstToken},
 };
+use itertools::Itertools;
 
 use crate::find_node_at_offset;
 
@@ -25,6 +28,7 @@ pub use self::{
     introduce_variable::introduce_variable,
     change_visibility::change_visibility,
     split_import::split_import,
+    replace_if_let_with_match::replace_if_let_with_match,
 };
 
 /// Return all the assists applicable at the given position.
@@ -37,6 +41,7 @@ pub fn assists(file: &SourceFile, range: TextRange) -> Vec<LocalEdit> {
         introduce_variable,
         change_visibility,
         split_import,
+        replace_if_let_with_match,
     ]
     .iter()
     .filter_map(|&assist| ctx.clone().apply(assist))
@@ -160,6 +165,13 @@ impl AssistBuilder {
     fn replace(&mut self, range: TextRange, replace_with: impl Into<String>) {
         self.edit.replace(range, replace_with.into())
     }
+    fn replace_node_and_indent(&mut self, node: &SyntaxNode, replace_with: impl Into<String>) {
+        let mut replace_with = replace_with.into();
+        if let Some(indent) = calc_indent(node) {
+            replace_with = reindent(&replace_with, indent)
+        }
+        self.replace(node.range(), replace_with)
+    }
     #[allow(unused)]
     fn delete(&mut self, range: TextRange) {
         self.edit.delete(range)
@@ -172,6 +184,17 @@ impl AssistBuilder {
     }
 }
 
+fn calc_indent(node: &SyntaxNode) -> Option<&str> {
+    let prev = node.prev_sibling()?;
+    let ws_text = ast::Whitespace::cast(prev)?.text();
+    ws_text.rfind('\n').map(|pos| &ws_text[pos + 1..])
+}
+
+fn reindent(text: &str, indent: &str) -> String {
+    let indent = format!("\n{}", indent);
+    text.lines().intersperse(&indent).collect()
+}
+
 #[cfg(test)]
 fn check_assist(assist: fn(AssistCtx) -> Option<Assist>, before: &str, after: &str) {
     crate::test_utils::check_action(before, after, |file, off| {
diff --git a/crates/ra_editor/src/assists/replace_if_let_with_match.rs b/crates/ra_editor/src/assists/replace_if_let_with_match.rs
new file mode 100644
index 000000000..30c371480
--- /dev/null
+++ b/crates/ra_editor/src/assists/replace_if_let_with_match.rs
@@ -0,0 +1,92 @@
+use ra_syntax::{
+    AstNode, SyntaxKind::{L_CURLY, R_CURLY, WHITESPACE},
+    ast,
+};
+
+use crate::assists::{AssistCtx, Assist};
+
+pub fn replace_if_let_with_match(ctx: AssistCtx) -> Option<Assist> {
+    let if_expr: &ast::IfExpr = ctx.node_at_offset()?;
+    let cond = if_expr.condition()?;
+    let pat = cond.pat()?;
+    let expr = cond.expr()?;
+    let then_block = if_expr.then_branch()?;
+    let else_block = if_expr.else_branch()?;
+
+    ctx.build("replace with match", |edit| {
+        let match_expr = build_match_expr(expr, pat, then_block, else_block);
+        edit.replace_node_and_indent(if_expr.syntax(), match_expr);
+        edit.set_cursor(if_expr.syntax().range().start())
+    })
+}
+
+fn build_match_expr(
+    expr: &ast::Expr,
+    pat1: &ast::Pat,
+    arm1: &ast::Block,
+    arm2: &ast::Block,
+) -> String {
+    let mut buf = String::new();
+    buf.push_str(&format!("match {} {{\n", expr.syntax().text()));
+    buf.push_str(&format!(
+        "    {} => {}\n",
+        pat1.syntax().text(),
+        format_arm(arm1)
+    ));
+    buf.push_str(&format!("    _ => {}\n", format_arm(arm2)));
+    buf.push_str("}");
+    buf
+}
+
+fn format_arm(block: &ast::Block) -> String {
+    match extract_expression(block) {
+        None => block.syntax().text().to_string(),
+        Some(e) => format!("{},", e.syntax().text()),
+    }
+}
+
+fn extract_expression(block: &ast::Block) -> Option<&ast::Expr> {
+    let expr = block.expr()?;
+    let non_trivial_children = block.syntax().children().filter(|it| {
+        !(it == &expr.syntax()
+            || it.kind() == L_CURLY
+            || it.kind() == R_CURLY
+            || it.kind() == WHITESPACE)
+    });
+    if non_trivial_children.count() > 0 {
+        return None;
+    }
+    Some(expr)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::assists::check_assist;
+
+    #[test]
+    fn test_replace_if_let_with_match_unwraps_simple_expressions() {
+        check_assist(
+            replace_if_let_with_match,
+            "
+impl VariantData {
+    pub fn is_struct(&self) -> bool {
+        if <|>let VariantData::Struct(..) = *self {
+            true
+        } else {
+            false
+        }
+    }
+}           ",
+            "
+impl VariantData {
+    pub fn is_struct(&self) -> bool {
+        <|>match *self {
+            VariantData::Struct(..) => true,
+            _ => false,
+        }
+    }
+}           ",
+        )
+    }
+}
diff --git a/crates/ra_editor/src/test_utils.rs b/crates/ra_editor/src/test_utils.rs
index bf40c92c0..dc2470aa3 100644
--- a/crates/ra_editor/src/test_utils.rs
+++ b/crates/ra_editor/src/test_utils.rs
@@ -13,7 +13,10 @@ pub fn check_action<F: Fn(&SourceFile, TextUnit) -> Option<LocalEdit>>(
     let result = f(&file, before_cursor_pos).expect("code action is not applicable");
     let actual = result.edit.apply(&before);
     let actual_cursor_pos = match result.cursor_position {
-        None => result.edit.apply_to_offset(before_cursor_pos).unwrap(),
+        None => result
+            .edit
+            .apply_to_offset(before_cursor_pos)
+            .expect("cursor position is affected by the edit"),
         Some(off) => off,
     };
     let actual = add_cursor(&actual, actual_cursor_pos);