zig fmt: handle shebang lines

closes #1546

std/zig/ast.zig

@@ -469,6 +469,7 @@ pub const Node = struct {
         doc_comments: ?*DocComment,
         decls: DeclList,
         eof_token: TokenIndex,
+        shebang: ?TokenIndex,
 
         pub const DeclList = SegmentedList(*Node, 4);
 
@@ -480,6 +481,7 @@ pub const Node = struct {
         }
 
         pub fn firstToken(self: *const Root) TokenIndex {
+            if (self.shebang) |shebang| return shebang;
             return if (self.decls.len == 0) self.eof_token else (self.decls.at(0).*).firstToken();
         }
 

std/zig/parse.zig

@@ -21,6 +21,7 @@ pub fn parse(allocator: *mem.Allocator, source: []const u8) !ast.Tree {
         .base = ast.Node{ .id = ast.Node.Id.Root },
         .decls = ast.Node.Root.DeclList.init(arena),
         .doc_comments = null,
+        .shebang = null,
         // initialized when we get the eof token
         .eof_token = undefined,
     });
@@ -41,6 +42,15 @@ pub fn parse(allocator: *mem.Allocator, source: []const u8) !ast.Tree {
     }
     var tok_it = tree.tokens.iterator(0);
 
+    // skip over shebang line
+    shebang: {
+        const shebang_tok_index = tok_it.index;
+        const shebang_tok_ptr = tok_it.peek() orelse break :shebang;
+        if (shebang_tok_ptr.id != Token.Id.ShebangLine) break :shebang;
+        root_node.shebang = shebang_tok_index;
+        _ = tok_it.next();
+    }
+
     // skip over line comments at the top of the file
     while (true) {
         const next_tok = tok_it.peek() orelse break;

std/zig/parser_test.zig

@@ -1,3 +1,11 @@
+test "zig fmt: shebang line" {
+    try testCanonical(
+        \\#!/usr/bin/env zig
+        \\pub fn main() void {}
+        \\
+    );
+}
+
 test "zig fmt: correctly move doc comments on struct fields" {
     try testTransform(
         \\pub const section_64 = extern struct {

std/zig/render.zig

@@ -67,8 +67,14 @@ fn renderRoot(
     stream: var,
     tree: *ast.Tree,
 ) (@typeOf(stream).Child.Error || Error)!void {
-    // render all the line comments at the beginning of the file
     var tok_it = tree.tokens.iterator(0);
+
+    // render the shebang line
+    if (tree.root_node.shebang) |shebang| {
+        try stream.write(tree.tokenSlice(shebang));
+    }
+
+    // render all the line comments at the beginning of the file
     while (tok_it.next()) |token| {
         if (token.id != Token.Id.LineComment) break;
         try stream.print("{}\n", mem.trimRight(u8, tree.tokenSlicePtr(token), " "));

std/zig/tokenizer.zig

@@ -145,6 +145,7 @@ pub const Token = struct {
         LineComment,
         DocComment,
         BracketStarBracket,
+        ShebangLine,
         Keyword_align,
         Keyword_and,
         Keyword_asm,
@@ -208,12 +209,25 @@ pub const Tokenizer = struct {
     }
 
     pub fn init(buffer: []const u8) Tokenizer {
+        if (mem.startsWith(u8, buffer, "#!")) {
+            const src_start = if (mem.indexOfScalar(u8, buffer, '\n')) |i| i + 1 else buffer.len;
+            return Tokenizer{
+                .buffer = buffer,
+                .index = src_start,
+                .pending_invalid_token = Token{
+                    .id = Token.Id.ShebangLine,
+                    .start = 0,
+                    .end = src_start,
+                },
+            };
+        } else {
             return Tokenizer{
                 .buffer = buffer,
                 .index = 0,
                 .pending_invalid_token = null,
             };
         }
+    }
 
     const State = enum {
         Start,