3 files changed, 128 insertions, 5 deletions

diff --git a/crates/ra_analysis/src/completion/complete_dot.rs b/crates/ra_analysis/src/completion/complete_dot.rs
new file mode 100644
index 000000000..fa62da210
--- /dev/null
+++ b/crates/ra_analysis/src/completion/complete_dot.rs
@@ -0,0 +1,98 @@
+use ra_syntax::ast::AstNode;
+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 module = if let Some(module) = &ctx.module {
+        module
+    } else {
+        return Ok(());
+    };
+    let function = if let Some(fn_def) = ctx.enclosing_fn {
+        hir::source_binder::function_from_module(ctx.db, module, fn_def)
+    } else {
+        return Ok(());
+    };
+    let receiver = if let Some(receiver) = ctx.dot_receiver {
+        receiver
+    } else {
+        return Ok(());
+    };
+    let infer_result = function.infer(ctx.db)?;
+    let receiver_ty = if let Some(ty) = infer_result.type_of_node(receiver.syntax()) {
+        ty
+    } else {
+        return Ok(());
+    };
+    if !ctx.is_method_call {
+        complete_fields(acc, ctx, receiver_ty)?;
+    }
+    Ok(())
+}
+
+fn complete_fields(acc: &mut Completions, ctx: &CompletionContext, ty: Ty) -> Cancelable<()> {
+    // TODO: autoderef etc.
+    match ty {
+        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_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_analysis/src/completion/completion_context.rs b/crates/ra_analysis/src/completion/completion_context.rs
index 064fbc6f7..12e98e870 100644
--- a/crates/ra_analysis/src/completion/completion_context.rs
+++ b/crates/ra_analysis/src/completion/completion_context.rs
@@ -31,6 +31,10 @@ pub(super) struct CompletionContext<'a> {
     pub(super) is_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<ast::Expr<'a>>,
+    /// If this is a method call in particular, i.e. the () are already there.
+    pub(super) is_method_call: bool,
 }
 
 impl<'a> CompletionContext<'a> {
@@ -54,6 +58,8 @@ impl<'a> CompletionContext<'a> {
             after_if: false,
             is_stmt: false,
             is_new_item: false,
+            dot_receiver: None,
+            is_method_call: false,
         };
         ctx.fill(original_file, position.offset);
         Ok(Some(ctx))
@@ -105,6 +111,12 @@ impl<'a> CompletionContext<'a> {
             _ => (),
         }
 
+        self.enclosing_fn = self
+            .leaf
+            .ancestors()
+            .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
+            .find_map(ast::FnDef::cast);
+
         let parent = match name_ref.syntax().parent() {
             Some(it) => it,
             None => return,
@@ -120,11 +132,6 @@ impl<'a> CompletionContext<'a> {
             }
             if path.qualifier().is_none() {
                 self.is_trivial_path = true;
-                self.enclosing_fn = self
-                    .leaf
-                    .ancestors()
-                    .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
-                    .find_map(ast::FnDef::cast);
 
                 self.is_stmt = match name_ref
                     .syntax()
@@ -145,6 +152,23 @@ impl<'a> CompletionContext<'a> {
                 }
             }
         }
+        if let Some(_field_expr) = ast::FieldExpr::cast(parent) {
+            self.dot_receiver = self
+                .leaf
+                .ancestors()
+                .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
+                .find_map(ast::FieldExpr::cast)
+                .and_then(ast::FieldExpr::expr);
+        }
+        if let Some(_method_call_expr) = ast::MethodCallExpr::cast(parent) {
+            self.dot_receiver = self
+                .leaf
+                .ancestors()
+                .take_while(|it| it.kind() != SOURCE_FILE && it.kind() != MODULE)
+                .find_map(ast::MethodCallExpr::cast)
+                .and_then(ast::MethodCallExpr::expr);
+            self.is_method_call = true;
+        }
     }
 }
 
diff --git a/crates/ra_analysis/src/completion/completion_item.rs b/crates/ra_analysis/src/completion/completion_item.rs
index 6d466c8bd..c9f9f495d 100644
--- a/crates/ra_analysis/src/completion/completion_item.rs
+++ b/crates/ra_analysis/src/completion/completion_item.rs
@@ -30,6 +30,7 @@ pub enum CompletionItemKind {
     Struct,
     Enum,
     Binding,
+    Field,
 }
 
 #[derive(Debug, PartialEq, Eq)]