feat: add an autofix for inserting an unsafe block to missing unsafe diagnostic

crates/ide-diagnostics/src/handlers/missing_unsafe.rs

@@ -1,4 +1,11 @@
-use crate::{Diagnostic, DiagnosticsContext};
+use hir::db::AstDatabase;
+use ide_db::{assists::Assist, source_change::SourceChange};
+use syntax::ast::{ExprStmt, LetStmt};
+use syntax::AstNode;
+use syntax::{ast, SyntaxNode};
+use text_edit::TextEdit;
+
+use crate::{fix, Diagnostic, DiagnosticsContext};
 
 // Diagnostic: missing-unsafe
 //
@@ -9,11 +16,60 @@ pub(crate) fn missing_unsafe(ctx: &DiagnosticsContext<'_>, d: &hir::MissingUnsaf
         "this operation is unsafe and requires an unsafe function or block",
         ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range,
     )
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::MissingUnsafe) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.expr.file_id)?;
+    let expr = d.expr.value.to_node(&root);
+
+    let node_to_add_unsafe_block = pick_best_node_to_add_unsafe_block(ctx, &expr);
+
+    let replacement = format!("unsafe {{ {} }}", node_to_add_unsafe_block.text());
+    let edit = TextEdit::replace(node_to_add_unsafe_block.text_range(), replacement);
+    let source_change =
+        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), edit);
+    Some(vec![fix("add_unsafe", "Add unsafe block", source_change, expr.syntax().text_range())])
+}
+
+// Find the let statement or expression statement closest to the `expr` in the
+// ancestor chain.
+//
+// Why don't we just add an unsafe block around the `expr`?
+//
+// Consider this example:
+// ```
+// STATIC_MUT += 1;
+// ```
+// We can't add an unsafe block to the left-hand side of an assignment.
+// ```
+// unsafe { STATIC_MUT } += 1;
+// ```
+//
+// Or this example:
+// ```
+// let z = STATIC_MUT.a;
+// ```
+// We can't add an unsafe block like this:
+// ```
+// let z = unsafe { STATIC_MUT } .a;
+// ```
+fn pick_best_node_to_add_unsafe_block(
+    ctx: &DiagnosticsContext<'_>,
+    expr: &ast::Expr,
+) -> SyntaxNode {
+    let Some(let_or_expr_stmt) = ctx.sema.ancestors_with_macros(expr.syntax().clone()).find(|node| {
+        LetStmt::can_cast(node.kind()) || ExprStmt::can_cast(node.kind())
+    }) else {
+        // Is this reachable?
+        return expr.syntax().clone();
+    };
+    let_or_expr_stmt
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::tests::check_diagnostics;
+    use crate::tests::{check_diagnostics, check_fix};
 
     #[test]
     fn missing_unsafe_diagnostic_with_raw_ptr() {
@@ -23,7 +79,7 @@ fn main() {
     let x = &5 as *const usize;
     unsafe { let y = *x; }
     let z = *x;
-}         //^^ error: this operation is unsafe and requires an unsafe function or block
+}         //^^💡 error: this operation is unsafe and requires an unsafe function or block
 "#,
         )
     }
@@ -48,9 +104,9 @@ unsafe fn unsafe_fn() {
 
 fn main() {
     unsafe_fn();
-  //^^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+  //^^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
     HasUnsafe.unsafe_fn();
-  //^^^^^^^^^^^^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+  //^^^^^^^^^^^^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
     unsafe {
         unsafe_fn();
         HasUnsafe.unsafe_fn();
@@ -72,7 +128,7 @@ static mut STATIC_MUT: Ty = Ty { a: 0 };
 
 fn main() {
     let x = STATIC_MUT.a;
-          //^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+          //^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
     unsafe {
         let x = STATIC_MUT.a;
     }
@@ -94,9 +150,135 @@ extern "rust-intrinsic" {
 fn main() {
     let _ = bitreverse(12);
     let _ = floorf32(12.0);
-          //^^^^^^^^^^^^^^ error: this operation is unsafe and requires an unsafe function or block
+          //^^^^^^^^^^^^^^💡 error: this operation is unsafe and requires an unsafe function or block
 }
 "#,
         );
     }
+
+    #[test]
+    fn add_unsafe_block_when_dereferencing_a_raw_pointer() {
+        check_fix(
+            r#"
+fn main() {
+    let x = &5 as *const usize;
+    let z = *x$0;
+}
+"#,
+            r#"
+fn main() {
+    let x = &5 as *const usize;
+    unsafe { let z = *x; }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn add_unsafe_block_when_calling_unsafe_function() {
+        check_fix(
+            r#"
+unsafe fn func() {
+    let x = &5 as *const usize;
+    let z = *x;
+}
+fn main() {
+    func$0();
+}
+"#,
+            r#"
+unsafe fn func() {
+    let x = &5 as *const usize;
+    let z = *x;
+}
+fn main() {
+    unsafe { func(); }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn add_unsafe_block_when_calling_unsafe_method() {
+        check_fix(
+            r#"
+struct S(usize);
+impl S {
+    unsafe fn func(&self) {
+        let x = &self.0 as *const usize;
+        let z = *x;
+    }
+}
+fn main() {
+    let s = S(5);
+    s.func$0();
+}
+"#,
+            r#"
+struct S(usize);
+impl S {
+    unsafe fn func(&self) {
+        let x = &self.0 as *const usize;
+        let z = *x;
+    }
+}
+fn main() {
+    let s = S(5);
+    unsafe { s.func(); }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn add_unsafe_block_when_accessing_mutable_static() {
+        check_fix(
+            r#"
+struct Ty {
+    a: u8,
+}
+
+static mut STATIC_MUT: Ty = Ty { a: 0 };
+
+fn main() {
+    let x = STATIC_MUT$0.a;
+}
+"#,
+            r#"
+struct Ty {
+    a: u8,
+}
+
+static mut STATIC_MUT: Ty = Ty { a: 0 };
+
+fn main() {
+    unsafe { let x = STATIC_MUT.a; }
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn add_unsafe_block_when_calling_unsafe_intrinsic() {
+        check_fix(
+            r#"
+extern "rust-intrinsic" {
+    pub fn floorf32(x: f32) -> f32;
+}
+
+fn main() {
+    let _ = floorf32$0(12.0);
+}
+"#,
+            r#"
+extern "rust-intrinsic" {
+    pub fn floorf32(x: f32) -> f32;
+}
+
+fn main() {
+    unsafe { let _ = floorf32(12.0); }
+}
+"#,
+        )
+    }
 }