Merge pull request #284 from zigtools/signature_help

Added signature help request handling.

.github/README.md

@@ -66,14 +66,14 @@ zig build config # Configure ZLS
 <!-- If this table grows too large, then delete this one and move it all over to the Wiki page about building from source. -->
 | Option | Type | Default Value | What it Does |
 | --- | --- | --- | --- |
-| `-Ddata_version` | `string` (master or 0.7.0) | master | The data file version. This selects the files in the `src/data` folder that correspond to the Zig version being served.|
+| `-Ddata_version` | `string` (master, 0.7.0 or 0.7.1) | master | The data file version. This selects the files in the `src/data` folder that correspond to the Zig version being served.|
 
 ### Configuration Options
 
 You can configure zls by providing a zls.json file.  
 zls will look for a zls.json configuration file in multiple locations with the following priority:  
 - In the local configuration folder of your OS (as provided by [known-folders](https://github.com/ziglibs/known-folders#folder-list))  
-- In the same directory as the executable  
+- In the global configuration folder of your OS (as provided by [known-folders](https://github.com/ziglibs/known-folders#folder-list))
 
 The following options are currently available.  
 

README.md

@@ -64,14 +64,14 @@ zls config # Configure ZLS
 <!-- If this table grows too large, then delete this one and move it all over to the Wiki page about building from source. -->
 | Option | Type | Default Value | What it Does |
 | --- | --- | --- | --- |
-| `-Ddata_version` | `string` (master or 0.7.0) | master | The data file version. This selects the files in the `src/data` folder that correspond to the Zig version being served.|
+| `-Ddata_version` | `string` (master, 0.7.0 or 0.7.1) | master | The data file version. This selects the files in the `src/data` folder that correspond to the Zig version being served.|
 
 ### Configuration Options
 
 You can configure zls by running `zls config`.  
 zls will look for a zls.json configuration file in multiple locations with the following priority:  
 - In the local configuration folder of your OS (as provided by [known-folders](https://github.com/ziglibs/known-folders#folder-list))  
-- In the same directory as the executable  
+- In the global configuration folder of your OS (as provided by [known-folders](https://github.com/ziglibs/known-folders#folder-list))
 
 The following options are currently available.  
 

build.zig

@@ -1,6 +1,5 @@
 const std = @import("std");
 const builtin = @import("builtin");
-// const build_options = @import("build_options")
 
 var builder: *std.build.Builder = undefined;
 
@@ -10,11 +9,10 @@ pub fn build(b: *std.build.Builder) !void {
 
     const mode = b.standardReleaseOptions();
     const exe = b.addExecutable("zls", "src/main.zig");
-
     exe.addBuildOption(
         []const u8,
         "data_version",
-        b.option([]const u8, "data_version", "The data version - either 0.7.0 or master.") orelse "master",
+        b.option([]const u8, "data_version", "The data version - 0.7.0, 0.7.1 or master.") orelse "master",
     );
 
     exe.addPackage(.{ .name = "known-folders", .path = "src/known-folders/known-folders.zig" });

src/analysis.zig

@@ -171,6 +171,46 @@ pub fn getFunctionSnippet(
     return buffer.toOwnedSlice();
 }
 
+/// Returns true if a function has a `self` parameter
+pub fn hasSelfParam(
+    arena: *std.heap.ArenaAllocator,
+    document_store: *DocumentStore,
+    handle: *DocumentStore.Handle,
+    func: ast.full.FnProto,
+) !bool {
+    // Non-decl prototypes cannot have a self parameter.
+    if (func.name_token == null) return false;
+    if (func.ast.params.len == 0) return false;
+
+    const tree = handle.tree;
+    var it = func.iterate(tree);
+    const param = it.next().?;
+    if (param.type_expr == 0) return false;
+
+    const token_starts = tree.tokens.items(.start);
+    const token_data = tree.nodes.items(.data);
+    const in_container = innermostContainer(handle, token_starts[func.ast.fn_token]);
+
+    if (try resolveTypeOfNode(document_store, arena, .{
+        .node = param.type_expr,
+        .handle = handle,
+    })) |resolved_type| {
+        if (std.meta.eql(in_container, resolved_type))
+            return true;
+    }
+
+    if (isPtrType(tree, param.type_expr)) {
+        if (try resolveTypeOfNode(document_store, arena, .{
+            .node = token_data[param.type_expr].rhs,
+            .handle = handle,
+        })) |resolved_prefix_op| {
+            if (std.meta.eql(in_container, resolved_prefix_op))
+                return true;
+        }
+    }
+    return false;
+}
+
 /// Gets a function signature (keywords, name, return value)
 pub fn getVariableSignature(tree: ast.Tree, var_decl: ast.full.VarDecl) []const u8 {
     const start = offsets.tokenLocation(tree, var_decl.ast.mut_token).start;
@@ -376,22 +416,6 @@ fn isBlock(tree: ast.Tree, node: ast.Node.Index) bool {
     };
 }
 
-/// Returns `true` when the given `node` is one of the call tags
-fn isCall(tree: ast.Tree, node: ast.Node.Index) bool {
-    return switch (tree.nodes.items(.tag)[node]) {
-        .call,
-        .call_comma,
-        .call_one,
-        .call_one_comma,
-        .async_call,
-        .async_call_comma,
-        .async_call_one,
-        .async_call_one_comma,
-        => true,
-        else => false,
-    };
-}
-
 fn findReturnStatementInternal(
     tree: ast.Tree,
     fn_decl: ast.full.FnProto,
@@ -946,7 +970,7 @@ pub fn resolveTypeOfNodeInternal(
             };
 
             return TypeWithHandle{
-                .type = .{ .data = .{ .pointer = rhs_node }, .is_type_val = false },
+                .type = .{ .data = .{ .pointer = rhs_node }, .is_type_val = rhs_type.type.is_type_val },
                 .handle = rhs_type.handle,
             };
         },
@@ -2250,6 +2274,21 @@ pub fn iterateSymbolsGlobal(
     return try iterateSymbolsGlobalInternal(store, arena, handle, source_index, callback, context, &use_trail);
 }
 
+pub fn innermostScope(handle: DocumentStore.Handle, source_index: usize) ast.Node.Index {
+    var current = handle.document_scope.scopes[0].data.container;
+    if (handle.document_scope.scopes.len == 1) return current;
+
+    for (handle.document_scope.scopes[1..]) |scope| {
+        if (source_index >= scope.range.start and source_index <= scope.range.end) {
+            switch (scope.data) {
+                .container, .function, .block => |node| current = node,
+                else => {},
+            }
+        }
+    }
+    return current;
+}
+
 pub fn innermostContainer(handle: *DocumentStore.Handle, source_index: usize) TypeWithHandle {
     var current = handle.document_scope.scopes[0].data.container;
     if (handle.document_scope.scopes.len == 1) return TypeWithHandle.typeVal(.{ .node = current, .handle = handle });
@@ -3094,19 +3133,7 @@ fn makeScopeInternal(
         .async_call_one_comma,
         => {
             var buf: [1]ast.Node.Index = undefined;
-            const call: ast.full.Call = switch (node_tag) {
-                .async_call,
-                .async_call_comma,
-                .call,
-                .call_comma,
-                => tree.callFull(node_idx),
-                .async_call_one,
-                .async_call_one_comma,
-                .call_one,
-                .call_one_comma,
-                => tree.callOne(&buf, node_idx),
-                else => unreachable,
-            };
+            const call = callFull(tree, node_idx, &buf).?;
 
             try makeScopeInternal(allocator, scopes, error_completions, enum_completions, tree, call.ast.fn_expr);
             for (call.ast.params) |param|

src/ast.zig

@@ -857,6 +857,21 @@ pub fn isBuiltinCall(tree: ast.Tree, node: ast.Node.Index) bool {
     };
 }
 
+pub fn isCall(tree: ast.Tree, node: ast.Node.Index) bool {
+    return switch (tree.nodes.items(.tag)[node]) {
+        .call,
+        .call_comma,
+        .call_one,
+        .call_one_comma,
+        .async_call,
+        .async_call_comma,
+        .async_call_one,
+        .async_call_one_comma,
+        => true,
+        else => false,
+    };
+}
+
 pub fn fnProto(tree: ast.Tree, node: ast.Node.Index, buf: *[1]ast.Node.Index) ?ast.full.FnProto {
     return switch (tree.nodes.items(.tag)[node]) {
         .fn_proto => tree.fnProto(node),
@@ -867,3 +882,19 @@ pub fn fnProto(tree: ast.Tree, node: ast.Node.Index, buf: *[1]ast.Node.Index) ?a
         else => null,
     };
 }
+
+pub fn callFull(tree: ast.Tree, node: ast.Node.Index, buf: *[1]ast.Node.Index) ?ast.full.Call {
+    return switch (tree.nodes.items(.tag)[node]) {
+        .async_call,
+        .async_call_comma,
+        .call,
+        .call_comma,
+        => tree.callFull(node),
+        .async_call_one,
+        .async_call_one_comma,
+        .call_one,
+        .call_one_comma,
+        => tree.callOne(buf, node),
+        else => null,
+    };
+}

src/data/generate-data.js

@@ -41,6 +41,7 @@ console.log(
     signature: []const u8,
     snippet: []const u8,
     documentation: []const u8,
+    arguments: []const []const u8,
 };
 
 pub const builtins = [_]Builtin{` +
@@ -49,11 +50,13 @@ pub const builtins = [_]Builtin{` +
         const first_paren_idx = builtin.code.indexOf('(');
         var snippet = builtin.code.substr(0, first_paren_idx + 1);
         var rest = builtin.code.substr(first_paren_idx + 1);
+        var args = [];
 
         if (rest[0] == ')') {
             snippet += ')';
         } else {
             snippet += "${1:"
+            args.push("");
 
             var arg_idx = 2;
             var paren_depth = 1;
@@ -69,10 +72,12 @@ pub const builtins = [_]Builtin{` +
                     }
                 } else if (char == '"') {
                     snippet += "\\\"";
+                    args[args.length - 1] += "\\\"";
                     continue;
                 } else if (char == ',' && paren_depth == 1) {
                     snippet += "}, ${" + arg_idx + ':';
                     arg_idx += 1;
+                    args.push("");
                     skip_space = true;
                     continue;
                 } else if (char == ' ' && skip_space) {
@@ -80,6 +85,7 @@ pub const builtins = [_]Builtin{` +
                 }
 
                 snippet += char;
+                args[args.length - 1] += char;
                 skip_space = false;
             }
         }
@@ -89,6 +95,9 @@ pub const builtins = [_]Builtin{` +
         .signature = "${builtin.code.replaceAll('"', "\\\"")}",
         .snippet = "${snippet}",
         .documentation =
-        \\\\${builtin.documentation.split('\n').join("\n        \\\\") + '\n'}    },`;
+        \\\\${builtin.documentation.split('\n').join("\n        \\\\")}
+        ,
+        .arguments = &.{${args.map(x => "\n            \"" + x + "\"").join(",") + ((args.length > 0) ? ",\n        " : "")}},
+    },`;
     }).join('\n') + "\n};\n"
 );

src/main.zig

@@ -124,6 +124,9 @@ const edit_not_applied_response =
 const no_completions_response =
     \\,"result":{"isIncomplete":false,"items":[]}}
 ;
+const no_signatures_response =
+    \\,"result":{"signatures":[]}}
+;
 const no_semantic_tokens_response =
     \\,"result":{"data":[]}}
 ;
@@ -326,6 +329,7 @@ fn typeToCompletion(
                 null,
                 orig_handle,
                 type_handle.type.is_type_val,
+                null,
                 config,
             );
         },
@@ -336,6 +340,7 @@ fn typeToCompletion(
             field_access.unwrapped,
             orig_handle,
             type_handle.type.is_type_val,
+            null,
             config,
         ),
         .primitive => {},
@@ -349,13 +354,13 @@ fn nodeToCompletion(
     unwrapped: ?analysis.TypeWithHandle,
     orig_handle: *DocumentStore.Handle,
     is_type_val: bool,
+    parent_is_type_val: ?bool,
     config: Config,
 ) error{OutOfMemory}!void {
     const node = node_handle.node;
     const handle = node_handle.handle;
     const tree = handle.tree;
     const node_tags = tree.nodes.items(.tag);
-    const datas = tree.nodes.items(.data);
     const token_tags = tree.tokens.items(.tag);
 
     const doc_kind: types.MarkupContent.Kind = if (client_capabilities.completion_doc_supports_md)
@@ -382,8 +387,17 @@ fn nodeToCompletion(
             .config = &config,
             .arena = arena,
             .orig_handle = orig_handle,
+            .parent_is_type_val = is_type_val,
         };
-        try analysis.iterateSymbolsContainer(&document_store, arena, node_handle, orig_handle, declToCompletion, context, !is_type_val);
+        try analysis.iterateSymbolsContainer(
+            &document_store,
+            arena,
+            node_handle,
+            orig_handle,
+            declToCompletion,
+            context,
+            !is_type_val,
+        );
     }
 
     if (is_type_val) return;
@@ -399,38 +413,9 @@ fn nodeToCompletion(
             const func = analysis.fnProto(tree, node, &buf).?;
             if (func.name_token) |name_token| {
                 const use_snippets = config.enable_snippets and client_capabilities.supports_snippets;
-
                 const insert_text = if (use_snippets) blk: {
-                    // TODO Also check if we are dot accessing from a type val and dont skip in that case.
-                    const skip_self_param = if (func.ast.params.len > 0) param_check: {
-                        const in_container = analysis.innermostContainer(handle, tree.tokens.items(.start)[func.ast.fn_token]);
-
-                        var it = func.iterate(tree);
-                        const param = it.next().?;
-
-                        if (param.type_expr == 0) break :param_check false;
-
-                        if (try analysis.resolveTypeOfNode(&document_store, arena, .{
-                            .node = param.type_expr,
-                            .handle = handle,
-                        })) |resolved_type| {
-                            if (std.meta.eql(in_container, resolved_type))
-                                break :param_check true;
-                        }
-
-                        if (analysis.isPtrType(tree, param.type_expr)) {
-                            if (try analysis.resolveTypeOfNode(&document_store, arena, .{
-                                .node = datas[param.type_expr].rhs,
-                                .handle = handle,
-                            })) |resolved_prefix_op| {
-                                if (std.meta.eql(in_container, resolved_prefix_op))
-                                    break :param_check true;
-                            }
-                        }
-
-                        break :param_check false;
-                    } else false;
-
+                    const skip_self_param = !(parent_is_type_val orelse true) and
+                        try analysis.hasSelfParam(arena, &document_store, handle, func);
                     break :blk try analysis.getFunctionSnippet(&arena.allocator, tree, func, skip_self_param);
                 } else tree.tokenSlice(func.name_token.?);
 
@@ -567,7 +552,7 @@ fn nodeToCompletion(
     }
 }
 
-fn identifierFromPosition(pos_index: usize, handle: DocumentStore.Handle) []const u8 {
+pub fn identifierFromPosition(pos_index: usize, handle: DocumentStore.Handle) []const u8 {
     const text = handle.document.text;
 
     if (pos_index + 1 >= text.len) return &[0]u8{};
@@ -754,7 +739,11 @@ fn hoverDefinitionBuiltin(arena: *std.heap.ArenaAllocator, id: types.RequestId,
                 .id = id,
                 .result = .{
                     .Hover = .{
-                        .contents = .{ .value = try std.fmt.allocPrint(&arena.allocator, "```zig\n{s}\n```\n{s}", .{ builtin.signature, builtin.documentation }) },
+                        .contents = .{ .value = try std.fmt.allocPrint(
+                            &arena.allocator,
+                            "```zig\n{s}\n```\n{s}",
+                            .{ builtin.signature, builtin.documentation },
+                        ) },
                     },
                 },
             });
@@ -945,13 +934,6 @@ fn referencesDefinitionLabel(arena: *std.heap.ArenaAllocator, id: types.RequestI
     });
 }
 
-const DeclToCompletionContext = struct {
-    completions: *std.ArrayList(types.CompletionItem),
-    config: *const Config,
-    arena: *std.heap.ArenaAllocator,
-    orig_handle: *DocumentStore.Handle,
-};
-
 fn hasComment(tree: ast.Tree, start_token: ast.TokenIndex, end_token: ast.TokenIndex) bool {
     const token_starts = tree.tokens.items(.start);
 
@@ -961,6 +943,14 @@ fn hasComment(tree: ast.Tree, start_token: ast.TokenIndex, end_token: ast.TokenI
     return std.mem.indexOf(u8, tree.source[start..end], "//") != null;
 }
 
+const DeclToCompletionContext = struct {
+    completions: *std.ArrayList(types.CompletionItem),
+    config: *const Config,
+    arena: *std.heap.ArenaAllocator,
+    orig_handle: *DocumentStore.Handle,
+    parent_is_type_val: ?bool = null,
+};
+
 fn declToCompletion(context: DeclToCompletionContext, decl_handle: analysis.DeclWithHandle) !void {
     const tree = decl_handle.handle.tree;
     switch (decl_handle.decl.*) {
@@ -971,6 +961,7 @@ fn declToCompletion(context: DeclToCompletionContext, decl_handle: analysis.Decl
             null,
             context.orig_handle,
             false,
+            context.parent_is_type_val,
             context.config.*,
         ),
         .param_decl => |param| {
@@ -1280,7 +1271,8 @@ fn initializeHandler(arena: *std.heap.ArenaAllocator, id: types.RequestId, req:
                 },
                 .capabilities = .{
                     .signatureHelpProvider = .{
-                        .triggerCharacters = &[_][]const u8{ "(", "," },
+                        .triggerCharacters = &.{"("},
+                        .retriggerCharacters = &.{","},
                     },
                     .textDocumentSync = .Full,
                     .renameProvider = true,
@@ -1398,39 +1390,77 @@ fn semanticTokensFullHandler(arena: *std.heap.ArenaAllocator, id: types.RequestI
     }
 }
 
-fn completionHandler(arena: *std.heap.ArenaAllocator, id: types.RequestId, req: requests.Completion, config: Config) !void {
+fn completionHandler(
+    arena: *std.heap.ArenaAllocator,
+    id: types.RequestId,
+    req: requests.Completion,
+    config: Config,
+) !void {
     const handle = document_store.getHandle(req.params.textDocument.uri) orelse {
         logger.warn("Trying to complete in non existent document {s}", .{req.params.textDocument.uri});
         return try respondGeneric(id, no_completions_response);
     };
 
-    if (req.params.position.character >= 0) {
-        const doc_position = try offsets.documentPosition(handle.document, req.params.position, offset_encoding);
-        const pos_context = try analysis.documentPositionContext(arena, handle.document, doc_position);
-        const use_snippets = config.enable_snippets and client_capabilities.supports_snippets;
+    if (req.params.position.character == 0)
+        return try respondGeneric(id, no_completions_response);
 
-        switch (pos_context) {
-            .builtin => try completeBuiltin(arena, id, config),
-            .var_access, .empty => try completeGlobal(arena, id, doc_position.absolute_index, handle, config),
-            .field_access => |range| try completeFieldAccess(arena, id, handle, doc_position, range, config),
-            .global_error_set => try completeError(arena, id, handle, config),
-            .enum_literal => try completeDot(arena, id, handle, config),
-            .label => try completeLabel(arena, id, doc_position.absolute_index, handle, config),
-            else => try respondGeneric(id, no_completions_response),
-        }
-    } else {
-        try respondGeneric(id, no_completions_response);
+    const doc_position = try offsets.documentPosition(handle.document, req.params.position, offset_encoding);
+    const pos_context = try analysis.documentPositionContext(arena, handle.document, doc_position);
+    const use_snippets = config.enable_snippets and client_capabilities.supports_snippets;
+
+    switch (pos_context) {
+        .builtin => try completeBuiltin(arena, id, config),
+        .var_access, .empty => try completeGlobal(arena, id, doc_position.absolute_index, handle, config),
+        .field_access => |range| try completeFieldAccess(arena, id, handle, doc_position, range, config),
+        .global_error_set => try completeError(arena, id, handle, config),
+        .enum_literal => try completeDot(arena, id, handle, config),
+        .label => try completeLabel(arena, id, doc_position.absolute_index, handle, config),
+        else => try respondGeneric(id, no_completions_response),
     }
 }
 
-fn signatureHelperHandler(arena: *std.heap.ArenaAllocator, id: types.RequestId, config: Config) !void {
-    // TODO Implement this
-    try respondGeneric(id,
-        \\,"result":{"signatures":[]}}
-    );
+fn signatureHelpHandler(
+    arena: *std.heap.ArenaAllocator,
+    id: types.RequestId,
+    req: requests.SignatureHelp,
+    config: Config,
+) !void {
+    const getSignatureInfo = @import("signature_help.zig").getSignatureInfo;
+    const handle = document_store.getHandle(req.params.textDocument.uri) orelse {
+        logger.warn("Trying to get signature help in non existent document {s}", .{req.params.textDocument.uri});
+        return try respondGeneric(id, no_signatures_response);
+    };
+
+    if (req.params.position.character == 0)
+        return try respondGeneric(id, no_signatures_response);
+
+    const doc_position = try offsets.documentPosition(handle.document, req.params.position, offset_encoding);
+    if (try getSignatureInfo(
+        &document_store,
+        arena,
+        handle,
+        doc_position.absolute_index,
+        data,
+    )) |sig_info| {
+        return try send(arena, types.Response{
+            .id = id,
+            .result = .{ .SignatureHelp = .{
+                .signatures = &[1]types.SignatureInformation{sig_info},
+                .activeSignature = 0,
+                .activeParameter = sig_info.activeParameter,
+            } },
+        });
+    }
+    return try respondGeneric(id, no_signatures_response);
 }
 
-fn gotoHandler(arena: *std.heap.ArenaAllocator, id: types.RequestId, req: requests.GotoDefinition, config: Config, resolve_alias: bool) !void {
+fn gotoHandler(
+    arena: *std.heap.ArenaAllocator,
+    id: types.RequestId,
+    req: requests.GotoDefinition,
+    config: Config,
+    resolve_alias: bool,
+) !void {
     const handle = document_store.getHandle(req.params.textDocument.uri) orelse {
         logger.warn("Trying to go to definition in non existent document {s}", .{req.params.textDocument.uri});
         return try respondGeneric(id, null_result_response);
@@ -1612,7 +1642,7 @@ fn processJsonRpc(arena: *std.heap.ArenaAllocator, parser: *std.json.Parser, jso
         .{ "textDocument/didClose", requests.CloseDocument, closeDocumentHandler },
         .{ "textDocument/semanticTokens/full", requests.SemanticTokensFull, semanticTokensFullHandler },
         .{ "textDocument/completion", requests.Completion, completionHandler },
-        .{ "textDocument/signatureHelp", void, signatureHelperHandler },
+        .{ "textDocument/signatureHelp", requests.SignatureHelp, signatureHelpHandler },
         .{ "textDocument/definition", requests.GotoDefinition, gotoDefinitionHandler },
         .{ "textDocument/typeDefinition", requests.GotoDefinition, gotoDefinitionHandler },
         .{ "textDocument/implementation", requests.GotoDefinition, gotoDefinitionHandler },

src/requests.zig

@@ -18,12 +18,22 @@ fn Default(comptime T: type, comptime default_value: T) type {
     };
 }
 
+pub fn ErrorUnwrappedReturnOf(comptime func: anytype) type {
+    return switch (@typeInfo(@TypeOf(func))) {
+        .Fn, .BoundFn => |fn_info| switch (@typeInfo(fn_info.return_type.?)) {
+            .ErrorUnion => |err_union| err_union.payload,
+            else => |T| return T,
+        },
+        else => unreachable,
+    };
+}
+
 fn Transform(comptime Original: type, comptime transform_fn: anytype) type {
     return struct {
         pub const original_type = Original;
         pub const transform = transform_fn;
 
-        value: @TypeOf(transform(@as(Original, undefined))),
+        value: ErrorUnwrappedReturnOf(transform_fn),
     };
 }
 
@@ -101,26 +111,34 @@ fn fromDynamicTreeInternal(arena: *std.heap.ArenaAllocator, value: std.json.Valu
         }
     } else if (T == std.json.Value) {
         out.* = value;
-    } else {
-        switch (T) {
-            bool => {
-                if (value != .Bool) return error.MalformedJson;
-                out.* = value.Bool;
-            },
-            i64 => {
-                if (value != .Integer) return error.MalformedJson;
-                out.* = value.Integer;
-            },
-            f64 => {
-                if (value != .Float) return error.MalformedJson;
-                out.* = value.Float;
-            },
-            []const u8 => {
-                if (value != .String) return error.MalformedJson;
-                out.* = value.String;
-            },
-            else => @compileError("Invalid type " ++ @typeName(T)),
-        }
+    } else if (comptime std.meta.trait.is(.Enum)(T)) {
+        const info = @typeInfo(T).Enum;
+        if (info.layout != .Auto)
+            @compileError("Only auto layout enums are allowed");
+
+        const TagType = info.tag_type;
+        if (value != .Integer) return error.MalformedJson;
+        out.* = std.meta.intToEnum(
+            T,
+            std.math.cast(TagType, value.Integer) catch return error.MalformedJson,
+        ) catch return error.MalformedJson;
+    } else if (comptime std.meta.trait.is(.Int)(T)) {
+        if (value != .Integer) return error.MalformedJson;
+        out.* = std.math.cast(T, value.Integer) catch return error.MalformedJson;
+    } else switch (T) {
+        bool => {
+            if (value != .Bool) return error.MalformedJson;
+            out.* = value.Bool;
+        },
+        f64 => {
+            if (value != .Float) return error.MalformedJson;
+            out.* = value.Float;
+        },
+        []const u8 => {
+            if (value != .String) return error.MalformedJson;
+            out.* = value.String;
+        },
+        else => @compileError("Invalid type " ++ @typeName(T)),
     }
 }
 
@@ -204,6 +222,23 @@ const TextDocumentIdentifierPositionRequest = struct {
     },
 };
 
+pub const SignatureHelp = struct {
+    params: struct {
+        textDocument: TextDocumentIdentifier,
+        position: types.Position,
+        context: ?struct {
+            triggerKind: enum {
+                invoked = 1,
+                trigger_character = 2,
+                content_change = 3,
+            },
+            triggerCharacter: ?[]const u8,
+            isRetrigger: bool,
+            activeSignatureHelp: ?types.SignatureHelp,
+        },
+    },
+};
+
 pub const Completion = TextDocumentIdentifierPositionRequest;
 pub const GotoDefinition = TextDocumentIdentifierPositionRequest;
 pub const GotoDeclaration = TextDocumentIdentifierPositionRequest;

src/signature_help.zig

@@ -0,0 +1,374 @@
+const std = @import("std");
+const analysis = @import("analysis.zig");
+const offsets = @import("offsets.zig");
+const DocumentStore = @import("document_store.zig");
+const types = @import("types.zig");
+const ast = std.zig.ast;
+const Token = std.zig.Token;
+const identifierFromPosition = @import("main.zig").identifierFromPosition;
+usingnamespace @import("ast.zig");
+
+fn fnProtoToSignatureInfo(
+    document_store: *DocumentStore,
+    arena: *std.heap.ArenaAllocator,
+    commas: u32,
+    skip_self_param: bool,
+    handle: *DocumentStore.Handle,
+    fn_node: ast.Node.Index,
+    proto: ast.full.FnProto,
+) !types.SignatureInformation {
+    const ParameterInformation = types.SignatureInformation.ParameterInformation;
+
+    const tree = handle.tree;
+    const token_starts = tree.tokens.items(.start);
+    const alloc = &arena.allocator;
+    const label = analysis.getFunctionSignature(tree, proto);
+    const proto_comments = types.MarkupContent{ .value = if (try analysis.getDocComments(
+        alloc,
+        tree,
+        fn_node,
+        .Markdown,
+    )) |dc|
+        dc
+    else
+        "" };
+
+    const arg_idx = if (skip_self_param) blk: {
+        const has_self_param = try analysis.hasSelfParam(arena, document_store, handle, proto);
+        break :blk commas + @boolToInt(has_self_param);
+    } else commas;
+
+    var params = std.ArrayListUnmanaged(ParameterInformation){};
+    var param_it = proto.iterate(tree);
+    while (param_it.next()) |param| {
+        const param_comments = if (param.first_doc_comment) |dc|
+            types.MarkupContent{ .value = try analysis.collectDocComments(
+                alloc,
+                tree,
+                dc,
+                .Markdown,
+            ) }
+        else
+            null;
+
+        var param_label_start: usize = 0;
+        var param_label_end: usize = 0;
+        if (param.comptime_noalias) |cn| {
+            param_label_start = token_starts[cn];
+            param_label_end = param_label_start + tree.tokenSlice(cn).len;
+        }
+        if (param.name_token) |nt| {
+            if (param_label_start == 0)
+                param_label_start = token_starts[nt];
+            param_label_end = token_starts[nt] + tree.tokenSlice(nt).len;
+        }
+        if (param.anytype_ellipsis3) |ae| {
+            if (param_label_start == 0)
+                param_label_start = token_starts[ae];
+            param_label_end = token_starts[ae] + tree.tokenSlice(ae).len;
+        }
+        if (param.type_expr != 0) {
+            if (param_label_start == 0)
+                param_label_start = token_starts[tree.firstToken(param.type_expr)];
+
+            const last_param_tok = lastToken(tree, param.type_expr);
+            param_label_end = token_starts[last_param_tok] + tree.tokenSlice(last_param_tok).len;
+        }
+        const param_label = tree.source[param_label_start..param_label_end];
+        try params.append(alloc, .{
+            .label = param_label,
+            .documentation = param_comments,
+        });
+    }
+    return types.SignatureInformation{
+        .label = label,
+        .documentation = proto_comments,
+        .parameters = params.items,
+        .activeParameter = arg_idx,
+    };
+}
+
+pub fn getSignatureInfo(
+    document_store: *DocumentStore,
+    arena: *std.heap.ArenaAllocator,
+    handle: *DocumentStore.Handle,
+    absolute_index: usize,
+    comptime data: type,
+) !?types.SignatureInformation {
+    const innermost_block = analysis.innermostScope(handle.*, absolute_index);
+    const tree = handle.tree;
+    const token_tags = tree.tokens.items(.tag);
+    const token_starts = tree.tokens.items(.start);
+
+    // Use the innermost scope to determine the earliest token we would need
+    //   to scan up to find a function or buitin call
+    const first_token = tree.firstToken(innermost_block);
+    // We start by finding the token that includes the current cursor position
+    const last_token = blk: {
+        if (token_starts[0] >= absolute_index)
+            return null;
+
+        var i: u32 = 1;
+        while (i < token_tags.len) : (i += 1) {
+            if (token_starts[i] >= absolute_index) {
+                break :blk i - 1;
+            }
+        }
+        break :blk @truncate(u32, token_tags.len - 1);
+    };
+
+    // We scan the tokens from last to first, adding and removing open and close
+    //   delimiter tokens to a stack, while keeping track of commas corresponding
+    //   to each of the blocks in a stack.
+    // When we encounter a dangling left parenthesis token, we continue scanning
+    //   backwards for a compatible possible function call lhs expression or a
+    //   single builtin token.
+    // When a function call expression is detected, it is resolved to a declaration
+    //   or a function type and the resulting function prototype is converted into
+    //   a signature information object.
+    const StackSymbol = enum {
+        l_paren,
+        r_paren,
+        l_brace,
+        r_brace,
+        l_bracket,
+        r_bracket,
+
+        fn from(tag: Token.Tag) @This() {
+            return switch (tag) {
+                .l_paren => .l_paren,
+                .r_paren => .r_paren,
+                .l_brace => .l_brace,
+                .r_brace => .r_brace,
+                .l_bracket => .l_bracket,
+                .r_bracket => .r_bracket,
+                else => unreachable,
+            };
+        }
+    };
+    const alloc = &arena.allocator;
+    var symbol_stack = try std.ArrayListUnmanaged(StackSymbol).initCapacity(alloc, 8);
+    var curr_commas: u32 = 0;
+    var comma_stack = try std.ArrayListUnmanaged(u32).initCapacity(alloc, 4);
+    var curr_token = last_token;
+    while (curr_token >= first_token and curr_token != 0) : (curr_token -= 1) {
+        switch (token_tags[curr_token]) {
+            .comma => curr_commas += 1,
+            .l_brace => {
+                curr_commas = comma_stack.popOrNull() orelse 0;
+                if (symbol_stack.items.len != 0) {
+                    const peek_sym = symbol_stack.items[symbol_stack.items.len - 1];
+                    switch (peek_sym) {
+                        .r_brace => {
+                            _ = symbol_stack.pop();
+                            continue;
+                        },
+                        .r_bracket, .r_paren => {
+                            return null;
+                        },
+                        else => {},
+                    }
+                }
+                try symbol_stack.append(alloc, .l_brace);
+            },
+            .l_bracket => {
+                curr_commas = comma_stack.popOrNull() orelse 0;
+                if (symbol_stack.items.len != 0) {
+                    const peek_sym = symbol_stack.items[symbol_stack.items.len - 1];
+                    switch (peek_sym) {
+                        .r_bracket => {
+                            _ = symbol_stack.pop();
+                            continue;
+                        },
+                        .r_brace, .r_paren => {
+                            return null;
+                        },
+                        else => {},
+                    }
+                }
+                try symbol_stack.append(alloc, .l_bracket);
+            },
+            .l_paren => {
+                const paren_commas = curr_commas;
+                curr_commas = comma_stack.popOrNull() orelse 0;
+                if (symbol_stack.items.len != 0) {
+                    const peek_sym = symbol_stack.items[symbol_stack.items.len - 1];
+                    switch (peek_sym) {
+                        .r_paren => {
+                            _ = symbol_stack.pop();
+                            continue;
+                        },
+                        .r_brace, .r_bracket => {
+                            return null;
+                        },
+                        else => {},
+                    }
+                }
+
+                // Try to find a function expression or a builtin identifier
+                if (curr_token == first_token)
+                    return null;
+
+                const expr_last_token = curr_token - 1;
+                if (token_tags[expr_last_token] == .builtin) {
+                    // Builtin token, find the builtin and construct signature information.
+                    for (data.builtins) |builtin| {
+                        if (std.mem.eql(u8, builtin.name, tree.tokenSlice(expr_last_token))) {
+                            const param_infos = try alloc.alloc(
+                                types.SignatureInformation.ParameterInformation,
+                                builtin.arguments.len,
+                            );
+                            for (param_infos) |*info, i| {
+                                info.* = .{
+                                    .label = builtin.arguments[i],
+                                    .documentation = null,
+                                };
+                            }
+                            return types.SignatureInformation{
+                                .label = builtin.signature,
+                                .documentation = .{
+                                    .value = builtin.documentation,
+                                },
+                                .parameters = param_infos,
+                                .activeParameter = paren_commas,
+                            };
+                        }
+                    }
+                    return null;
+                }
+                // Scan for a function call lhs expression.
+                var state: union(enum) {
+                    any,
+                    in_bracket: u32,
+                    in_paren: u32,
+                } = .any;
+                var i = expr_last_token;
+                const expr_first_token = while (i > first_token) : (i -= 1) {
+                    switch (state) {
+                        .in_bracket => |*count| if (token_tags[i] == .r_bracket) {
+                            count.* += 1;
+                        } else if (token_tags[i] == .l_bracket) {
+                            count.* -= 1;
+                            if (count.* == 0)
+                                state = .any;
+                        },
+                        .in_paren => |*count| if (token_tags[i] == .r_paren) {
+                            count.* += 1;
+                        } else if (token_tags[i] == .l_paren) {
+                            count.* -= 1;
+                            if (count.* == 0)
+                                state = .any;
+                        },
+                        .any => switch (token_tags[i]) {
+                            .r_bracket => state = .{ .in_bracket = 1 },
+                            .r_paren => state = .{ .in_paren = 1 },
+                            .identifier,
+                            .period,
+                            .period_asterisk,
+                            => {},
+                            else => break i + 1,
+                        },
+                    }
+                } else first_token + 1;
+                if (state != .any or expr_first_token > expr_last_token) {
+                    try symbol_stack.append(alloc, .l_paren);
+                    continue;
+                }
+                const expr_start = token_starts[expr_first_token];
+                const last_token_slice = tree.tokenSlice(expr_last_token);
+                const expr_end = token_starts[expr_last_token] + last_token_slice.len;
+                const expr_source = tree.source[expr_start..expr_end];
+                // Resolve the expression.
+                var tokenizer = std.zig.Tokenizer.init(expr_source);
+                if (try analysis.getFieldAccessType(
+                    document_store,
+                    arena,
+                    handle,
+                    expr_start,
+                    &tokenizer,
+                )) |result| {
+                    const type_handle = result.unwrapped orelse result.original;
+                    var node = switch (type_handle.type.data) {
+                        .other => |n| n,
+                        else => {
+                            try symbol_stack.append(alloc, .l_paren);
+                            continue;
+                        },
+                    };
+
+                    var buf: [1]ast.Node.Index = undefined;
+                    if (fnProto(type_handle.handle.tree, node, &buf)) |proto| {
+                        return try fnProtoToSignatureInfo(
+                            document_store,
+                            arena,
+                            paren_commas,
+                            false,
+                            type_handle.handle,
+                            node,
+                            proto,
+                        );
+                    }
+
+                    const name = identifierFromPosition(expr_end - 1, handle.*);
+                    if (name.len == 0) {
+                        try symbol_stack.append(alloc, .l_paren);
+                        continue;
+                    }
+
+                    const skip_self_param = !type_handle.type.is_type_val;
+                    const decl_handle = (try analysis.lookupSymbolContainer(
+                        document_store,
+                        arena,
+                        .{ .node = node, .handle = type_handle.handle },
+                        name,
+                        true,
+                    )) orelse {
+                        try symbol_stack.append(alloc, .l_paren);
+                        continue;
+                    };
+                    var res_handle = decl_handle.handle;
+                    node = switch (decl_handle.decl.*) {
+                        .ast_node => |n| n,
+                        else => {
+                            try symbol_stack.append(alloc, .l_paren);
+                            continue;
+                        },
+                    };
+
+                    if (try analysis.resolveVarDeclAlias(
+                        document_store,
+                        arena,
+                        .{ .node = node, .handle = decl_handle.handle },
+                    )) |resolved| {
+                        switch (resolved.decl.*) {
+                            .ast_node => |n| {
+                                res_handle = resolved.handle;
+                                node = n;
+                            },
+                            else => {},
+                        }
+                    }
+
+                    if (fnProto(res_handle.tree, node, &buf)) |proto| {
+                        return try fnProtoToSignatureInfo(
+                            document_store,
+                            arena,
+                            paren_commas,
+                            skip_self_param,
+                            res_handle,
+                            node,
+                            proto,
+                        );
+                    }
+                }
+            },
+            .r_brace, .r_paren, .r_bracket => |tag| {
+                try comma_stack.append(alloc, curr_commas);
+                curr_commas = 0;
+                try symbol_stack.append(alloc, StackSymbol.from(tag));
+            },
+            else => {},
+        }
+    }
+    return null;
+}

src/types.zig

@@ -31,6 +31,7 @@ pub const Hover = struct {
 
 /// Params of a response (result)
 pub const ResponseParams = union(enum) {
+    SignatureHelp: SignatureHelp,
     CompletionList: CompletionList,
     Location: Location,
     Hover: Hover,
@@ -289,12 +290,32 @@ pub const WorkspaceFolder = struct {
     name: []const u8,
 };
 
+pub const SignatureInformation = struct {
+    pub const ParameterInformation = struct {
+        // TODO Can also send a pair of encoded offsets
+        label: []const u8,
+        documentation: ?MarkupContent,
+    };
+
+    label: []const u8,
+    documentation: ?MarkupContent,
+    parameters: ?[]const ParameterInformation,
+    activeParameter: ?u32,
+};
+
+pub const SignatureHelp = struct {
+    signatures: ?[]const SignatureInformation,
+    activeSignature: ?u32,
+    activeParameter: ?u32,
+};
+
 // Only includes options we set in our initialize result.
 const InitializeResult = struct {
     offsetEncoding: []const u8,
     capabilities: struct {
         signatureHelpProvider: struct {
             triggerCharacters: []const []const u8,
+            retriggerCharacters: []const []const u8,
         },
         textDocumentSync: enum {
             None = 0,

tests/sessions.zig

@@ -153,6 +153,6 @@ test "Requesting utf-8 offset encoding" {
 
     try sendRequest(shutdown_message, process);
     try consumeOutputAndWait(process, .{
-        \\{"jsonrpc":"2.0","id":0,"result":{"offsetEncoding":"utf-8","capabilities":{"signatureHelpProvider":{"triggerCharacters":["(",","]},"textDocumentSync":1,"renameProvider":true,"completionProvider":{"resolveProvider":false,"triggerCharacters":[".",":","@"]},"documentHighlightProvider":false,"hoverProvider":true,"codeActionProvider":false,"declarationProvider":true,"definitionProvider":true,"typeDefinitionProvider":true,"implementationProvider":false,"referencesProvider":true,"documentSymbolProvider":true,"colorProvider":false,"documentFormattingProvider":true,"documentRangeFormattingProvider":false,"foldingRangeProvider":false,"selectionRangeProvider":false,"workspaceSymbolProvider":false,"rangeProvider":false,"documentProvider":true,"workspace":{"workspaceFolders":{"supported":false,"changeNotifications":false}},"semanticTokensProvider":{"full":true,"range":false,"legend":{"tokenTypes":["type","parameter","variable","enumMember","field","errorTag","function","keyword","comment","string","number","operator","builtin","label","keywordLiteral"],"tokenModifiers":["namespace","struct","enum","union","opaque","declaration","async","documentation","generic"]}}},"serverInfo":{"name":"zls","version":"0.1.0"}}}
+        \\{"jsonrpc":"2.0","id":0,"result":{"offsetEncoding":"utf-8","capabilities":{"signatureHelpProvider":{"triggerCharacters":["("],"retriggerCharacters":[","]},"textDocumentSync":1,"renameProvider":true,"completionProvider":{"resolveProvider":false,"triggerCharacters":[".",":","@"]},"documentHighlightProvider":false,"hoverProvider":true,"codeActionProvider":false,"declarationProvider":true,"definitionProvider":true,"typeDefinitionProvider":true,"implementationProvider":false,"referencesProvider":true,"documentSymbolProvider":true,"colorProvider":false,"documentFormattingProvider":true,"documentRangeFormattingProvider":false,"foldingRangeProvider":false,"selectionRangeProvider":false,"workspaceSymbolProvider":false,"rangeProvider":false,"documentProvider":true,"workspace":{"workspaceFolders":{"supported":false,"changeNotifications":false}},"semanticTokensProvider":{"full":true,"range":false,"legend":{"tokenTypes":["type","parameter","variable","enumMember","field","errorTag","function","keyword","comment","string","number","operator","builtin","label","keywordLiteral"],"tokenModifiers":["namespace","struct","enum","union","opaque","declaration","async","documentation","generic"]}}},"serverInfo":{"name":"zls","version":"0.1.0"}}}
     });
 }