8 files changed, 210 insertions, 5 deletions

diff --git a/crates/ra_ide_api/src/expand_macro.rs b/crates/ra_ide_api/src/expand_macro.rs
new file mode 100644
index 000000000..48dc90932
--- /dev/null
+++ b/crates/ra_ide_api/src/expand_macro.rs
@@ -0,0 +1,112 @@
+//! FIXME: write short doc here
+
+use crate::{db::RootDatabase, FilePosition};
+use ra_db::SourceDatabase;
+use rustc_hash::FxHashMap;
+
+use hir::db::AstDatabase;
+use ra_syntax::{
+    algo::{find_node_at_offset, replace_descendants},
+    ast::{self},
+    AstNode, NodeOrToken, SyntaxKind, SyntaxNode, WalkEvent,
+};
+
+fn insert_whitespaces(syn: SyntaxNode) -> String {
+    let mut res = String::new();
+
+    let mut token_iter = syn
+        .preorder_with_tokens()
+        .filter_map(|event| {
+            if let WalkEvent::Enter(NodeOrToken::Token(token)) = event {
+                Some(token)
+            } else {
+                None
+            }
+        })
+        .peekable();
+
+    while let Some(token) = token_iter.next() {
+        res += &token.text().to_string();
+        if token.kind().is_keyword()
+            || token.kind().is_literal()
+            || token.kind() == SyntaxKind::IDENT
+        {
+            if !token_iter.peek().map(|it| it.kind().is_punct()).unwrap_or(false) {
+                res += " ";
+            }
+        }
+    }
+
+    res
+}
+
+fn expand_macro_recur(
+    db: &RootDatabase,
+    source: hir::Source<&SyntaxNode>,
+    macro_call: &ast::MacroCall,
+) -> Option<SyntaxNode> {
+    let analyzer = hir::SourceAnalyzer::new(db, source, None);
+    let expansion = analyzer.expand(db, &macro_call)?;
+    let expanded: SyntaxNode = db.parse_or_expand(expansion.file_id())?;
+
+    let children = expanded.descendants().filter_map(ast::MacroCall::cast);
+    let mut replaces = FxHashMap::default();
+
+    for child in children.into_iter() {
+        let source = hir::Source::new(expansion.file_id(), source.ast);
+        let new_node = expand_macro_recur(db, source, &child)?;
+
+        replaces.insert(child.syntax().clone().into(), new_node.into());
+    }
+
+    Some(replace_descendants(&expanded, &replaces))
+}
+
+pub(crate) fn expand_macro(db: &RootDatabase, position: FilePosition) -> Option<(String, String)> {
+    let parse = db.parse(position.file_id);
+    let file = parse.tree();
+    let name_ref = find_node_at_offset::<ast::NameRef>(file.syntax(), position.offset)?;
+    let mac = name_ref.syntax().ancestors().find_map(ast::MacroCall::cast)?;
+
+    let source = hir::Source::new(position.file_id.into(), mac.syntax());
+
+    let expanded = expand_macro_recur(db, source, &mac)?;
+
+    // FIXME:
+    // macro expansion may lose all white space information
+    // But we hope someday we can use ra_fmt for that
+    let res = insert_whitespaces(expanded);
+    Some((name_ref.text().to_string(), res))
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::mock_analysis::analysis_and_position;
+
+    fn check_expand_macro(fixture: &str, expected: (&str, &str)) {
+        let (analysis, pos) = analysis_and_position(fixture);
+
+        let result = analysis.expand_macro(pos).unwrap().unwrap();
+        assert_eq!(result, (expected.0.to_string(), expected.1.to_string()));
+    }
+
+    #[test]
+    fn macro_expand_recursive_expansion() {
+        check_expand_macro(
+            r#"
+        //- /lib.rs
+        macro_rules! bar {
+            () => { fn  b() {} }
+        }
+        macro_rules! foo {
+            () => { bar!(); }
+        }
+        macro_rules! baz {
+            () => { foo!(); }
+        }        
+        f<|>oo!();
+        "#,
+            ("foo", "fn b(){}"),
+        );
+    }
+}
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index 110ddcd62..d1b73ef6f 100644
--- a/crates/ra_ide_api/src/lib.rs
+++ b/crates/ra_ide_api/src/lib.rs
@@ -42,6 +42,7 @@ mod display;
 mod inlay_hints;
 mod wasm_shims;
 mod expand;
+mod expand_macro;
 
 #[cfg(test)]
 mod marks;
@@ -296,6 +297,10 @@ impl Analysis {
         self.with_db(|db| syntax_tree::syntax_tree(&db, file_id, text_range))
     }
 
+    pub fn expand_macro(&self, position: FilePosition) -> Cancelable<Option<(String, String)>> {
+        self.with_db(|db| expand_macro::expand_macro(db, position))
+    }
+
     /// Returns an edit to remove all newlines in the range, cleaning up minor
     /// stuff like trailing commas.
     pub fn join_lines(&self, frange: FileRange) -> Cancelable<SourceChange> {
diff --git a/crates/ra_lsp_server/src/main_loop.rs b/crates/ra_lsp_server/src/main_loop.rs
index 379dab438..f828efdee 100644
--- a/crates/ra_lsp_server/src/main_loop.rs
+++ b/crates/ra_lsp_server/src/main_loop.rs
@@ -436,6 +436,7 @@ fn on_request(
         })?
         .on::<req::AnalyzerStatus>(handlers::handle_analyzer_status)?
         .on::<req::SyntaxTree>(handlers::handle_syntax_tree)?
+        .on::<req::ExpandMacro>(handlers::handle_expand_macro)?
         .on::<req::OnTypeFormatting>(handlers::handle_on_type_formatting)?
         .on::<req::DocumentSymbolRequest>(handlers::handle_document_symbol)?
         .on::<req::WorkspaceSymbol>(handlers::handle_workspace_symbol)?
diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index 20f9aee13..783b0a827 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -47,6 +47,21 @@ pub fn handle_syntax_tree(world: WorldSnapshot, params: req::SyntaxTreeParams) -
     Ok(res)
 }
 
+pub fn handle_expand_macro(
+    world: WorldSnapshot,
+    params: req::ExpandMacroParams,
+) -> Result<Option<(String, String)>> {
+    let _p = profile("handle_expand_macro");
+    let file_id = params.text_document.try_conv_with(&world)?;
+    let line_index = world.analysis().file_line_index(file_id)?;
+    let offset = params.position.map(|p| p.conv_with(&line_index));
+
+    match offset {
+        None => Ok(None),
+        Some(offset) => Ok(world.analysis().expand_macro(FilePosition { file_id, offset })?),
+    }
+}
+
 pub fn handle_selection_range(
     world: WorldSnapshot,
     params: req::SelectionRangeParams,
diff --git a/crates/ra_lsp_server/src/req.rs b/crates/ra_lsp_server/src/req.rs
index d25fc5726..dbc0e9624 100644
--- a/crates/ra_lsp_server/src/req.rs
+++ b/crates/ra_lsp_server/src/req.rs
@@ -45,6 +45,21 @@ pub struct SyntaxTreeParams {
     pub range: Option<Range>,
 }
 
+pub enum ExpandMacro {}
+
+impl Request for ExpandMacro {
+    type Params = ExpandMacroParams;
+    type Result = Option<(String, String)>;
+    const METHOD: &'static str = "rust-analyzer/expandMacro";
+}
+
+#[derive(Deserialize, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct ExpandMacroParams {
+    pub text_document: TextDocumentIdentifier,
+    pub position: Option<Position>,
+}
+
 pub enum SelectionRangeRequest {}
 
 impl Request for SelectionRangeRequest {
diff --git a/editors/code/src/commands/expand_macro.ts b/editors/code/src/commands/expand_macro.ts
new file mode 100644
index 000000000..bf1923190
--- /dev/null
+++ b/editors/code/src/commands/expand_macro.ts
@@ -0,0 +1,45 @@
+import * as vscode from 'vscode';
+import { Position, TextDocumentIdentifier } from 'vscode-languageclient';
+import { Server } from '../server';
+
+type ExpandMacroResult = [string, string]
+
+function code_format([name, text]: [string, string]): vscode.MarkdownString {
+    const markdown = new vscode.MarkdownString(`#### Recursive expansion of ${name}! macro`);
+    markdown.appendCodeblock(text, 'rust');    
+    return markdown;
+}
+
+export class ExpandMacroHoverProvider implements vscode.HoverProvider {
+    public provideHover(
+        document: vscode.TextDocument,
+        position: vscode.Position,
+        token: vscode.CancellationToken,
+    ): Thenable<vscode.Hover | null> | null {
+        async function handle() {
+            const request: MacroExpandParams = {
+                textDocument: { uri: document.uri.toString() },
+                position,
+            };
+            const result = await Server.client.sendRequest<ExpandMacroResult>(
+                'rust-analyzer/expandMacro',
+                request
+            );
+            if (result != null) {
+                const formated = code_format(result);
+                return new vscode.Hover(formated);
+            }
+
+            return null;
+        };
+
+        return handle();
+    }
+}
+
+
+interface MacroExpandParams {
+    textDocument: TextDocumentIdentifier;
+    position: Position;
+}
+
diff --git a/editors/code/src/commands/index.ts b/editors/code/src/commands/index.ts
index c194bd2ea..2ade6d331 100644
--- a/editors/code/src/commands/index.ts
+++ b/editors/code/src/commands/index.ts
@@ -1,5 +1,6 @@
 import * as analyzerStatus from './analyzer_status';
 import * as applySourceChange from './apply_source_change';
+import * as expandMacro from './expand_macro';
 import * as inlayHints from './inlay_hints';
 import * as joinLines from './join_lines';
 import * as matchingBrace from './matching_brace';
@@ -11,6 +12,7 @@ import * as syntaxTree from './syntaxTree';
 export {
     analyzerStatus,
     applySourceChange,
+    expandMacro,
     joinLines,
     matchingBrace,
     parentModule,
diff --git a/editors/code/src/extension.ts b/editors/code/src/extension.ts
index c06928d12..1dfa6046f 100644
--- a/editors/code/src/extension.ts
+++ b/editors/code/src/extension.ts
@@ -3,6 +3,7 @@ import * as lc from 'vscode-languageclient';
 
 import * as commands from './commands';
 import { CargoWatchProvider } from './commands/cargo_watch';
+import { ExpandMacroHoverProvider } from './commands/expand_macro'
 import { HintsUpdater } from './commands/inlay_hints';
 import {
     interactivelyStartCargoWatch,
@@ -91,11 +92,11 @@ export function activate(context: vscode.ExtensionContext) {
     const allNotifications: Iterable<
         [string, lc.GenericNotificationHandler]
     > = [
-        [
-            'rust-analyzer/publishDecorations',
-            notifications.publishDecorations.handle
-        ]
-    ];
+            [
+                'rust-analyzer/publishDecorations',
+                notifications.publishDecorations.handle
+            ]
+        ];
     const syntaxTreeContentProvider = new SyntaxTreeContentProvider();
 
     // The events below are plain old javascript events, triggered and handled by vscode
@@ -121,6 +122,15 @@ export function activate(context: vscode.ExtensionContext) {
         context.subscriptions
     );
 
+    const expandMacroContentProvider = new ExpandMacroHoverProvider();
+
+    disposeOnDeactivation(
+        vscode.languages.registerHoverProvider(
+            'rust',
+            expandMacroContentProvider
+        )
+    );
+
     const startServer = () => Server.start(allNotifications);
     const reloadCommand = () => reloadServer(startServer);