Implement parsing of user-defined functions

Summary:
This diff implements only the parsing part of user-defined functions. The renderer currently rejects them and support for them will be added in a future diff.

The change here adds in a new kind of `function_call` in the AST called `user_defined`. User-defined functions are accessed via a `variable_lookup`.

Additionally, names are changed to match nomenclature used in the spec (builtin), and error messages have been updated to be more consistent with others.

Reviewed By: createdbysk

Differential Revision: D67587583

fbshipit-source-id: 12ba36ff8153b2bf751ea4f0568cd2b6f3aba8bc

thrift/compiler/whisker/ast.cc

@@ -66,24 +66,31 @@ std::string partial_apply::path_string() const {
 
 std::string expression::to_string() const {
   return detail::variant_match(
-      content,
+      which,
       [](const variable_lookup& v) { return v.chain_string(); },
       [](const function_call& f) {
         std::string out = fmt::format("({}", f.name());
-        for (const auto& arg : f.args) {
+        for (const auto& arg : f.positional_arguments) {
           fmt::format_to(std::back_inserter(out), " {}", arg.to_string());
         }
+        for (const auto& [name, arg] : f.named_arguments) {
+          fmt::format_to(
+              std::back_inserter(out), " {}={}", name, arg.value->to_string());
+        }
         out += ")";
         return out;
       });
 }
 
-std::string_view expression::function_call::name() const {
+std::string expression::function_call::name() const {
   return detail::variant_match(
       which,
-      [&](function_call::not_tag) { return "not"; },
-      [&](function_call::and_tag) { return "and"; },
-      [&](function_call::or_tag) { return "or"; });
+      [](function_call::builtin_not) -> std::string { return "not"; },
+      [](function_call::builtin_and) -> std::string { return "and"; },
+      [](function_call::builtin_or) -> std::string { return "or"; },
+      [](const function_call::user_defined& f) -> std::string {
+        return f.name.chain_string();
+      });
 }
 
 std::string_view pragma_statement::to_string() const {

thrift/compiler/whisker/ast.h

@@ -18,6 +18,8 @@
 
 #include <thrift/compiler/whisker/source_location.h>
 
+#include <map>
+#include <memory>
 #include <optional>
 #include <string>
 #include <variant>
@@ -153,50 +155,122 @@ struct variable_lookup {
 struct expression {
   source_range loc;
   struct function_call {
+    /**
+     * Base class for all built-in functions.
+     */
+    struct builtin {};
+    /**
+     * Binary functions which are also associative and can be "chained", such as
+     * `(and arg1 ... argN)`, `(or arg1 ... argN)` etc.
+     */
+    struct builtin_binary_associative {};
+
     /**
      * The `(not arg1)` function.
      */
-    struct not_tag {
+    struct builtin_not : builtin {
       // Remove in C++20 which introduces comparison operator synthesis
-      friend bool operator==(const not_tag&, const not_tag&) { return true; }
-      WHISKER_DEFINE_OPERATOR_INEQUALITY(not_tag)
+      friend bool operator==(const builtin_not&, const builtin_not&) {
+        return true;
+      }
+      WHISKER_DEFINE_OPERATOR_INEQUALITY(builtin_not)
     };
-    struct and_or_tag {}; // for convenience of writing matchers
+
     /**
      * The `(and arg1 ... argN)` function.
      */
-    struct and_tag : and_or_tag {
+    struct builtin_and : builtin, builtin_binary_associative {
       // Remove in C++20 which introduces comparison operator synthesis
-      friend bool operator==(const and_tag&, const and_tag&) { return true; }
-      WHISKER_DEFINE_OPERATOR_INEQUALITY(and_tag)
+      friend bool operator==(const builtin_and&, const builtin_and&) {
+        return true;
+      }
+      WHISKER_DEFINE_OPERATOR_INEQUALITY(builtin_and)
     };
+
     /**
      * The `(or arg1 ... argN)` function.
      */
-    struct or_tag : and_or_tag {
+    struct builtin_or : builtin, builtin_binary_associative {
+      // Remove in C++20 which introduces comparison operator synthesis
+      friend bool operator==(const builtin_or&, const builtin_or&) {
+        return true;
+      }
+      WHISKER_DEFINE_OPERATOR_INEQUALITY(builtin_or)
+    };
+
+    /**
+     * A user-defined function call whose name is variable (chain of
+     * identifiers).
+     *
+     * Example:
+     *   `(my_lib.snake_case "FooBar")` // "foo_bar"
+     */
+    struct user_defined {
+      variable_lookup name;
+
+      friend bool operator==(const user_defined& lhs, const user_defined& rhs) {
+        return lhs.name == rhs.name;
+      }
       // Remove in C++20 which introduces comparison operator synthesis
-      friend bool operator==(const or_tag&, const or_tag&) { return true; }
-      WHISKER_DEFINE_OPERATOR_INEQUALITY(or_tag)
+      WHISKER_DEFINE_OPERATOR_INEQUALITY(user_defined)
     };
-    std::variant<not_tag, and_tag, or_tag> which;
-    std::vector<expression> args;
+
+    std::variant<builtin_not, builtin_and, builtin_or, user_defined> which;
+
+    /**
+     * Unnamed arguments that are identified by their ordering in the function
+     * invocation.
+     */
+    std::vector<expression> positional_arguments;
+
+    struct named_argument {
+      identifier name;
+      // Using the heap to avoid mutually recursion with `expression`.
+      // Using std::shared_ptr so that this struct is copyable.
+      std::shared_ptr<expression> value;
+
+      friend bool operator==(
+          const named_argument& lhs, const named_argument& rhs) {
+        static const auto as_tuple = [](const named_argument& arg) {
+          return std::tie(arg.name, *arg.value);
+        };
+        return as_tuple(lhs) == as_tuple(rhs);
+      }
+      // Remove in C++20 which introduces comparison operator synthesis
+      WHISKER_DEFINE_OPERATOR_INEQUALITY(named_argument)
+    };
+    /**
+     * Named arguments that are identified by their name, with no restrictions
+     * on their ordering. Every argument must have a unique identifier. All
+     * named arguments must appear after all positional arguments.
+     *
+     * Using std::map for stable ordering when printing the AST.
+     */
+    std::map<std::string_view, named_argument> named_arguments;
+
+    /**
+     * The name of the function call lookup as seen in the source code.
+     */
+    std::string name() const;
 
     friend bool operator==(const function_call& lhs, const function_call& rhs) {
-      return std::tie(lhs.which, lhs.args) == std::tie(rhs.which, rhs.args);
+      static const auto as_tuple = [](const function_call& f) {
+        // Ignore the source range of the function call.
+        return std::tie(f.which, f.positional_arguments, f.named_arguments);
+      };
+      return as_tuple(lhs) == as_tuple(rhs);
     }
     // Remove in C++20 which introduces comparison operator synthesis
     WHISKER_DEFINE_OPERATOR_INEQUALITY(function_call)
-
-    std::string_view name() const;
   };
-  std::variant<variable_lookup, function_call> content;
+  std::variant<variable_lookup, function_call> which;
 
   /**
    * Determines if two expressions are syntactically equivalent, excluding their
    * location in source code.
    */
   friend bool operator==(const expression& lhs, const expression& rhs) {
-    return lhs.content == rhs.content;
+    return lhs.which == rhs.which;
   }
   // Remove in C++20 which introduces comparison operator synthesis
   WHISKER_DEFINE_OPERATOR_INEQUALITY(expression)

thrift/compiler/whisker/parser.cc

@@ -995,51 +995,143 @@ class parser {
     if (!try_consume_token(&scan, tok::l_paren)) {
       return no_parse_result();
     }
+    scan = scan.make_fresh();
 
     function_call func;
+
     if (try_consume_token(&scan, tok::kw_not)) {
-      func.which = function_call::not_tag{};
+      func.which = function_call::builtin_not{};
     } else if (try_consume_token(&scan, tok::kw_and)) {
-      func.which = function_call::and_tag{};
+      func.which = function_call::builtin_and{};
     } else if (try_consume_token(&scan, tok::kw_or)) {
-      func.which = function_call::or_tag{};
+      func.which = function_call::builtin_or{};
+    } else if (parse_result lookup = parse_variable_lookup(scan)) {
+      func.which = function_call::user_defined{
+          std::move(lookup).consume_and_advance(&scan)};
     } else {
-      report_fatal_error(scan, "unrecognized function {}", scan.peek());
-    }
+      report_expected(scan, "function-lookup in function-call");
+    }
+
+    using named_argument_entry =
+        decltype(function_call::named_arguments)::value_type;
+    // argument → { positional-argument | named-argument }
+    // positional-argument → { expression }
+    // named-argument → { identifier ~ "=" ~ expression }
+    const auto parse_argument = [this, &func](parser_scan_window scan)
+        -> parse_result<std::variant<ast::expression, named_argument_entry>> {
+      assert(scan.empty());
+      const token& id = scan.peek();
+      if (id.kind == tok::identifier && scan.next().peek().kind == tok::eq) {
+        scan = scan.next(2).make_fresh();
+        if (parse_result expression = parse_expression(scan)) {
+          return {
+              named_argument_entry{
+                  id.string_value(),
+                  function_call::named_argument{
+                      ast::identifier{id.range, std::string(id.string_value())},
+                      std::make_unique<ast::expression>(
+                          std::move(expression).consume_and_advance(&scan))}},
+              scan};
+        }
+        report_expected(scan, "expression in named argument");
+      }
+
+      assert(scan.empty());
+      if (parse_result expression = parse_expression(scan)) {
+        return {
+            ast::expression{std::move(expression).consume_and_advance(&scan)},
+            scan};
+      }
+      if (scan.peek().kind == tok::eq) {
+        report_fatal_error(
+            scan,
+            "expected identifier to precede {} in named argument for function call '{}'",
+            tok::eq,
+            func.name());
+      }
+      return no_parse_result();
+    };
 
-    while (parse_result cond = parse_expression(scan.make_fresh())) {
-      func.args.push_back(std::move(cond).consume_and_advance(&scan));
+    // All named arguments must be at the end of the argument list
+    bool named_arg_seen = false;
+    while (parse_result arg = parse_argument(scan.make_fresh())) {
+      auto arg_scan_start = scan;
+      detail::variant_match(
+          std::move(arg).consume_and_advance(&scan),
+          [&](ast::expression&& positional) {
+            if (named_arg_seen) {
+              report_fatal_error(
+                  scan,
+                  "unexpected positional argument '{}' after named arguments in function call '{}'",
+                  positional.to_string(),
+                  func.name());
+            }
+            func.positional_arguments.push_back(std::move(positional));
+          },
+          [&](named_argument_entry&& named) {
+            named_arg_seen = true;
+            std::string_view name = named.first;
+            if (const auto& [_, inserted] =
+                    func.named_arguments.insert(std::move(named));
+                !inserted) {
+              report_fatal_error(
+                  arg_scan_start,
+                  "duplicate named argument '{}' in function call '{}'",
+                  name,
+                  func.name());
+            }
+          });
     }
+    scan = scan.make_fresh();
 
+    // Validate positional arguments
     detail::variant_match(
         func.which,
-        [&](function_call::not_tag) {
-          if (func.args.size() != 1) {
+        [&](const function_call::builtin_not&) {
+          if (func.positional_arguments.size() != 1) {
             report_fatal_error(
                 scan,
-                "expected 1 argument for helper `not` but got {}",
-                func.args.size());
+                "expected 1 argument for function 'not' but found {}",
+                func.positional_arguments.size());
           }
         },
-        [&](function_call::and_or_tag&) {
-          if (func.args.size() <= 1) {
+        [&](const function_call::builtin_binary_associative&) {
+          if (func.positional_arguments.size() <= 1) {
             report_fatal_error(
                 scan,
-                "expected at least 2 arguments for helper `{}` but got {}",
+                "expected at least 2 arguments for function '{}' but found {}",
                 func.name(),
-                func.args.size());
+                func.positional_arguments.size());
           }
+        },
+        [](const function_call::user_defined&) {
+          // User-defined functions can have any number of arguments
+        });
+
+    // Validate named arguments
+    detail::variant_match(
+        func.which,
+        [&](const function_call::builtin&) {
+          if (!func.named_arguments.empty()) {
+            report_fatal_error(
+                scan,
+                "named arguments not allowed for function '{}'",
+                func.name());
+          }
+        },
+        [](const function_call::user_defined&) {
+          // User-defined functions can have any number of named arguments
         });
 
     if (!try_consume_token(&scan, tok::r_paren)) {
-      report_fatal_error(
+      report_expected(
           scan,
-          "expected `)` to close helper `{}` but got `{}`",
-          func.name(),
-          scan.peek());
+          fmt::format("{} to close function '{}'", tok::r_paren, func.name()));
     }
 
-    return {{scan.with_start(scan_start).range(), std::move(func)}, scan};
+    return {
+        ast::expression{scan.with_start(scan_start).range(), std::move(func)},
+        scan};
   }
 
   // let-statement →

thrift/compiler/whisker/print_ast.cc

@@ -18,10 +18,7 @@
 #include <thrift/compiler/whisker/print_ast.h>
 #include <thrift/compiler/whisker/tree_printer.h>
 
-#include <iterator>
-#include <memory>
 #include <ostream>
-#include <string_view>
 
 #include <fmt/core.h>