17 files changed, 358 insertions, 27 deletions

diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index b70d005fb..5bc41533c 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -5,6 +5,7 @@ on:
     branches:
       - master
       - staging
+      - trying
 
 jobs:
   rust:
diff --git a/Cargo.lock b/Cargo.lock
index fe08edd29..ef3735197 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1180,7 +1180,7 @@ dependencies = [
  "once_cell 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "ra_parser 0.1.0",
  "ra_text_edit 0.1.0",
- "rowan 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rowan 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_lexer 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "smol_str 0.1.15 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1445,7 +1445,7 @@ dependencies = [
 
 [[package]]
 name = "rowan"
-version = "0.6.3"
+version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1993,7 +1993,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum relative-path 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bedde000f40f2921ce439ea165c9c53fd629bfa115140c72e22aceacb4a21954"
 "checksum remove_dir_all 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)" = "4a83fa3702a688b9359eccba92d153ac33fd2e8462f9e0e3fdf155239ea7792e"
 "checksum ron 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "2ece421e0c4129b90e4a35b6f625e472e96c552136f5093a2f4fa2bbb75a62d5"
-"checksum rowan 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)" = "fc3a6fb2a35518af7cab43ec4e21ca82eb086a8b3bb1739e426dc3923d459607"
+"checksum rowan 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d3a241900475bf2ba302061550ff50c82b45095ca95d23d1872345793fd42407"
 "checksum rustc-demangle 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)" = "4c691c0e608126e00913e33f0ccf3727d5fc84573623b8d65b2df340b5201783"
 "checksum rustc-hash 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "7540fc8b0c49f096ee9c961cda096467dce8084bec6bdca2fc83895fd9b28cb8"
 "checksum rustc_lexer 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "c86aae0c77166108c01305ee1a36a1e77289d7dc6ca0a3cd91ff4992de2d16a5"
diff --git a/crates/ra_hir/src/source_binder.rs b/crates/ra_hir/src/source_binder.rs
index f0ed8e2b2..5d3196c2a 100644
--- a/crates/ra_hir/src/source_binder.rs
+++ b/crates/ra_hir/src/source_binder.rs
@@ -140,7 +140,7 @@ impl Expansion {
         exp_info.map_token_down(token)
     }
 
-    fn file_id(&self) -> HirFileId {
+    pub fn file_id(&self) -> HirFileId {
         self.macro_call_id.as_file(MacroFileKind::Items)
     }
 }
diff --git a/crates/ra_hir_expand/src/quote.rs b/crates/ra_hir_expand/src/quote.rs
index 35133d216..65a35e52f 100644
--- a/crates/ra_hir_expand/src/quote.rs
+++ b/crates/ra_hir_expand/src/quote.rs
@@ -172,12 +172,12 @@ impl_to_to_tokentrees! {
     u32 => self { tt::Literal{text: self.to_string().into()} };
     usize => self { tt::Literal{text: self.to_string().into()}};
     i32 => self { tt::Literal{text: self.to_string().into()}};
-    &str => self { tt::Literal{text: self.to_string().into()}};
-    String => self { tt::Literal{text: self.into()}};
     tt::Leaf => self { self };
     tt::Literal => self { self };
     tt::Ident => self { self };
-    tt::Punct => self { self }
+    tt::Punct => self { self };
+    &str => self { tt::Literal{text: format!("{:?}", self.escape_default().to_string()).into()}};
+    String => self { tt::Literal{text: format!("{:?}", self.escape_default().to_string()).into()}}
 }
 
 #[cfg(test)]
@@ -200,7 +200,7 @@ mod tests {
         let a = 20;
         assert_eq!(quote!(#a).to_string(), "20");
         let s: String = "hello".into();
-        assert_eq!(quote!(#s).to_string(), "hello");
+        assert_eq!(quote!(#s).to_string(), "\"hello\"");
     }
 
     fn mk_ident(name: &str) -> tt::Ident {
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..e9eb2a7fb
--- /dev/null
+++ b/crates/ra_ide_api/src/expand_macro.rs
@@ -0,0 +1,178 @@
+//! This modules implements "expand macro" functionality in the IDE
+
+use crate::{db::RootDatabase, FilePosition};
+use hir::db::AstDatabase;
+use ra_db::SourceDatabase;
+use rustc_hash::FxHashMap;
+
+use ra_syntax::{
+    algo::{find_node_at_offset, replace_descendants},
+    ast::{self},
+    AstNode, NodeOrToken, SyntaxKind, SyntaxNode, WalkEvent, T,
+};
+
+pub struct ExpandedMacro {
+    pub name: String,
+    pub expansion: String,
+}
+
+pub(crate) fn expand_macro(db: &RootDatabase, position: FilePosition) -> Option<ExpandedMacro> {
+    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 expansion = insert_whitespaces(expanded);
+    Some(ExpandedMacro { name: name_ref.text().to_string(), expansion })
+}
+
+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 macro_file_id = expansion.file_id();
+    let expanded: SyntaxNode = db.parse_or_expand(macro_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(macro_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))
+}
+
+// FIXME: It would also be cool to share logic here and in the mbe tests,
+// which are pretty unreadable at the moment.
+fn insert_whitespaces(syn: SyntaxNode) -> String {
+    use SyntaxKind::*;
+
+    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();
+
+    let mut indent = 0;
+    let mut last: Option<SyntaxKind> = None;
+
+    while let Some(token) = token_iter.next() {
+        let mut is_next = |f: fn(SyntaxKind) -> bool, default| -> bool {
+            token_iter.peek().map(|it| f(it.kind())).unwrap_or(default)
+        };
+        let is_last = |f: fn(SyntaxKind) -> bool, default| -> bool {
+            last.map(|it| f(it)).unwrap_or(default)
+        };
+
+        res += &match token.kind() {
+            k @ _
+                if (k.is_keyword() || k.is_literal() || k == IDENT)
+                    && is_next(|it| !it.is_punct(), true) =>
+            {
+                token.text().to_string() + " "
+            }
+            L_CURLY if is_next(|it| it != R_CURLY, true) => {
+                indent += 1;
+                format!(" {{\n{}", "  ".repeat(indent))
+            }
+            R_CURLY if is_last(|it| it != L_CURLY, true) => {
+                indent = indent.checked_sub(1).unwrap_or(0);
+                format!("\n}}{}", "  ".repeat(indent))
+            }
+            R_CURLY => {
+                indent = indent.checked_sub(1).unwrap_or(0);
+                format!("}}\n{}", "  ".repeat(indent))
+            }
+            T![;] => format!(";\n{}", "  ".repeat(indent)),
+            T![->] => " -> ".to_string(),
+            T![=] => " = ".to_string(),
+            T![=>] => " => ".to_string(),
+            _ => token.text().to_string(),
+        };
+
+        last = Some(token.kind());
+    }
+
+    res
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::mock_analysis::analysis_and_position;
+    use insta::assert_snapshot;
+
+    fn check_expand_macro(fixture: &str) -> ExpandedMacro {
+        let (analysis, pos) = analysis_and_position(fixture);
+        analysis.expand_macro(pos).unwrap().unwrap()
+    }
+
+    #[test]
+    fn macro_expand_recursive_expansion() {
+        let res = check_expand_macro(
+            r#"
+        //- /lib.rs
+        macro_rules! bar {
+            () => { fn  b() {} }
+        }
+        macro_rules! foo {
+            () => { bar!(); }
+        }
+        macro_rules! baz {
+            () => { foo!(); }
+        }        
+        f<|>oo!();
+        "#,
+        );
+
+        assert_eq!(res.name, "foo");
+        assert_snapshot!(res.expansion, @r###"
+fn b(){}
+"###);
+    }
+
+    #[test]
+    fn macro_expand_multiple_lines() {
+        let res = check_expand_macro(
+            r#"
+        //- /lib.rs
+        macro_rules! foo {
+            () => { 
+                fn some_thing() -> u32 {
+                    let a = 0;
+                    a + 10
+                }
+            }
+        }
+        f<|>oo!();
+        "#,
+        );
+
+        assert_eq!(res.name, "foo");
+        assert_snapshot!(res.expansion, @r###"
+fn some_thing() -> u32 {
+  let a = 0;
+  a+10
+}        
+"###);
+    }
+}
diff --git a/crates/ra_ide_api/src/lib.rs b/crates/ra_ide_api/src/lib.rs
index 110ddcd62..57ed97147 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;
@@ -65,6 +66,7 @@ pub use crate::{
     completion::{CompletionItem, CompletionItemKind, InsertTextFormat},
     diagnostics::Severity,
     display::{file_structure, FunctionSignature, NavigationTarget, StructureNode},
+    expand_macro::ExpandedMacro,
     feature_flags::FeatureFlags,
     folding_ranges::{Fold, FoldKind},
     hover::HoverResult,
@@ -296,6 +298,10 @@ impl Analysis {
         self.with_db(|db| syntax_tree::syntax_tree(&db, file_id, text_range))
     }
 
+    pub fn expand_macro(&self, position: FilePosition) -> Cancelable<Option<ExpandedMacro>> {
+        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..0461bf385 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -47,6 +47,24 @@ pub fn handle_syntax_tree(world: WorldSnapshot, params: req::SyntaxTreeParams) -
     Ok(res)
 }
 
+pub fn handle_expand_macro(
+    world: WorldSnapshot,
+    params: req::ExpandMacroParams,
+) -> Result<Option<req::ExpandedMacro>> {
+    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) => {
+            let res = world.analysis().expand_macro(FilePosition { file_id, offset })?;
+            Ok(res.map(|it| req::ExpandedMacro { name: it.name, expansion: it.expansion }))
+        }
+    }
+}
+
 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..39361b7e8 100644
--- a/crates/ra_lsp_server/src/req.rs
+++ b/crates/ra_lsp_server/src/req.rs
@@ -45,6 +45,28 @@ pub struct SyntaxTreeParams {
     pub range: Option<Range>,
 }
 
+#[derive(Serialize, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct ExpandedMacro {
+    pub name: String,
+    pub expansion: String,
+}
+
+pub enum ExpandMacro {}
+
+impl Request for ExpandMacro {
+    type Params = ExpandMacroParams;
+    type Result = Option<ExpandedMacro>;
+    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/crates/ra_syntax/Cargo.toml b/crates/ra_syntax/Cargo.toml
index 45a18a73f..5db2b58c0 100644
--- a/crates/ra_syntax/Cargo.toml
+++ b/crates/ra_syntax/Cargo.toml
@@ -12,7 +12,7 @@ doctest = false
 
 [dependencies]
 itertools = "0.8.0"
-rowan = "0.6.1"
+rowan = "0.7.0"
 rustc_lexer = "0.1.0"
 rustc-hash = "1.0.1"
 arrayvec = "0.5.1"
diff --git a/crates/ra_syntax/src/algo.rs b/crates/ra_syntax/src/algo.rs
index 7cfea70f9..1c075082a 100644
--- a/crates/ra_syntax/src/algo.rs
+++ b/crates/ra_syntax/src/algo.rs
@@ -134,23 +134,19 @@ pub fn insert_children(
         to_green_element(element)
     });
 
-    let old_children = parent.green().children();
+    let mut old_children = parent.green().children().map(|it| match it {
+        NodeOrToken::Token(it) => NodeOrToken::Token(it.clone()),
+        NodeOrToken::Node(it) => NodeOrToken::Node(it.clone()),
+    });
 
     let new_children = match &position {
-        InsertPosition::First => {
-            to_insert.chain(old_children.iter().cloned()).collect::<Box<[_]>>()
-        }
-        InsertPosition::Last => old_children.iter().cloned().chain(to_insert).collect::<Box<[_]>>(),
+        InsertPosition::First => to_insert.chain(old_children).collect::<Box<[_]>>(),
+        InsertPosition::Last => old_children.chain(to_insert).collect::<Box<[_]>>(),
         InsertPosition::Before(anchor) | InsertPosition::After(anchor) => {
             let take_anchor = if let InsertPosition::After(_) = position { 1 } else { 0 };
             let split_at = position_of_child(parent, anchor.clone()) + take_anchor;
-            let (before, after) = old_children.split_at(split_at);
-            before
-                .iter()
-                .cloned()
-                .chain(to_insert)
-                .chain(after.iter().cloned())
-                .collect::<Box<[_]>>()
+            let before = old_children.by_ref().take(split_at).collect::<Vec<_>>();
+            before.into_iter().chain(to_insert).chain(old_children).collect::<Box<[_]>>()
         }
     };
 
@@ -168,13 +164,16 @@ pub fn replace_children(
 ) -> SyntaxNode {
     let start = position_of_child(parent, to_delete.start().clone());
     let end = position_of_child(parent, to_delete.end().clone());
-    let old_children = parent.green().children();
+    let mut old_children = parent.green().children().map(|it| match it {
+        NodeOrToken::Token(it) => NodeOrToken::Token(it.clone()),
+        NodeOrToken::Node(it) => NodeOrToken::Node(it.clone()),
+    });
 
-    let new_children = old_children[..start]
-        .iter()
-        .cloned()
+    let before = old_children.by_ref().take(start).collect::<Vec<_>>();
+    let new_children = before
+        .into_iter()
         .chain(to_insert.map(to_green_element))
-        .chain(old_children[end + 1..].iter().cloned())
+        .chain(old_children.skip(end + 1 - start))
         .collect::<Box<[_]>>();
     with_children(parent, new_children)
 }
diff --git a/crates/ra_syntax/src/ast/extensions.rs b/crates/ra_syntax/src/ast/extensions.rs
index 761b2435c..4851dacb2 100644
--- a/crates/ra_syntax/src/ast/extensions.rs
+++ b/crates/ra_syntax/src/ast/extensions.rs
@@ -32,7 +32,7 @@ impl ast::NameRef {
 }
 
 fn text_of_first_token(node: &SyntaxNode) -> &SmolStr {
-    node.green().children().first().and_then(|it| it.as_token()).unwrap().text()
+    node.green().children().next().and_then(|it| it.into_token()).unwrap().text()
 }
 
 impl ast::Attr {
diff --git a/docs/user/features.md b/docs/user/features.md
index c160dd70b..309d2775d 100644
--- a/docs/user/features.md
+++ b/docs/user/features.md
@@ -81,6 +81,10 @@ Join selected lines into one, smartly fixing up whitespace and trailing commas.
 Shows the parse tree of the current file. It exists mostly for debugging
 rust-analyzer itself.
 
+#### Expand Macro Recursively
+
+Shows the full macro expansion of the macro at current cursor.
+
 #### Status
 
 Shows internal statistic about memory usage of rust-analyzer
diff --git a/editors/code/package.json b/editors/code/package.json
index fbf675d46..e21dfa174 100644
--- a/editors/code/package.json
+++ b/editors/code/package.json
@@ -92,6 +92,11 @@
                 "category": "Rust Analyzer"
             },
             {
+                "command": "rust-analyzer.expandMacro",
+                "title": "Expand macro recursively",
+                "category": "Rust Analyzer"
+            },
+            {
                 "command": "rust-analyzer.matchingBrace",
                 "title": "Find matching brace",
                 "category": "Rust Analyzer"
diff --git a/editors/code/src/commands/expand_macro.ts b/editors/code/src/commands/expand_macro.ts
new file mode 100644
index 000000000..34e0c8fb3
--- /dev/null
+++ b/editors/code/src/commands/expand_macro.ts
@@ -0,0 +1,83 @@
+import * as vscode from 'vscode';
+import { Position, TextDocumentIdentifier } from 'vscode-languageclient';
+import { Server } from '../server';
+
+export const expandMacroUri = vscode.Uri.parse(
+    'rust-analyzer://expandMacro/[EXPANSION].rs'
+);
+
+export class ExpandMacroContentProvider
+    implements vscode.TextDocumentContentProvider {
+    public eventEmitter = new vscode.EventEmitter<vscode.Uri>();
+
+    public provideTextDocumentContent(
+        uri: vscode.Uri
+    ): vscode.ProviderResult<string> {
+        async function handle() {
+            const editor = vscode.window.activeTextEditor;
+            if (editor == null) {
+                return '';
+            }
+
+            const position = editor.selection.active;
+            const request: MacroExpandParams = {
+                textDocument: { uri: editor.document.uri.toString() },
+                position
+            };
+            const expanded = await Server.client.sendRequest<ExpandedMacro>(
+                'rust-analyzer/expandMacro',
+                request
+            );
+
+            if (expanded == null) {
+                return 'Not available';
+            }
+
+            return code_format(expanded);
+        }
+
+        return handle();
+    }
+
+    get onDidChange(): vscode.Event<vscode.Uri> {
+        return this.eventEmitter.event;
+    }
+}
+
+// Opens the virtual file that will show the syntax tree
+//
+// The contents of the file come from the `TextDocumentContentProvider`
+export function createHandle(provider: ExpandMacroContentProvider) {
+    return async () => {
+        const uri = expandMacroUri;
+
+        const document = await vscode.workspace.openTextDocument(uri);
+
+        provider.eventEmitter.fire(uri);
+
+        return vscode.window.showTextDocument(
+            document,
+            vscode.ViewColumn.Two,
+            true
+        );
+    };
+}
+
+interface MacroExpandParams {
+    textDocument: TextDocumentIdentifier;
+    position: Position;
+}
+
+interface ExpandedMacro {
+    name: string;
+    expansion: string;
+}
+
+function code_format(expanded: ExpandedMacro): string {
+    let result = `// Recursive expansion of ${expanded.name}! macro\n`;
+    result += '// ' + '='.repeat(result.length - 3);
+    result += '\n\n';
+    result += expanded.expansion;
+
+    return result;
+}
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..683497dfd 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 { ExpandMacroContentProvider } from './commands/expand_macro';
 import { HintsUpdater } from './commands/inlay_hints';
 import {
     interactivelyStartCargoWatch,
@@ -97,6 +98,7 @@ export function activate(context: vscode.ExtensionContext) {
         ]
     ];
     const syntaxTreeContentProvider = new SyntaxTreeContentProvider();
+    const expandMacroContentProvider = new ExpandMacroContentProvider();
 
     // The events below are plain old javascript events, triggered and handled by vscode
     vscode.window.onDidChangeActiveTextEditor(
@@ -109,11 +111,21 @@ export function activate(context: vscode.ExtensionContext) {
             syntaxTreeContentProvider
         )
     );
+    disposeOnDeactivation(
+        vscode.workspace.registerTextDocumentContentProvider(
+            'rust-analyzer',
+            expandMacroContentProvider
+        )
+    );
 
     registerCommand(
         'rust-analyzer.syntaxTree',
         commands.syntaxTree.createHandle(syntaxTreeContentProvider)
     );
+    registerCommand(
+        'rust-analyzer.expandMacro',
+        commands.expandMacro.createHandle(expandMacroContentProvider)
+    );
 
     vscode.workspace.onDidChangeTextDocument(
         events.changeTextDocument.createHandler(syntaxTreeContentProvider),