Add syntax for package and library (#792)

Doesn't add much logic, only takes advantage of parser structure for the ordering enforcement.

Note import_nonexistent tests should probably fail, but writing import tests needs a chain of functionality, and I figured I'd just start adding some to validate the syntax (not adding existent imports because that'd require multi-file structure).

executable_semantics/syntax/BUILD

@@ -37,6 +37,7 @@ cc_library(
         "//common:check",
         "//common:ostream",
         "//common:string_helpers",
+        "//executable_semantics/ast",
         "//executable_semantics/ast:declaration",
         "//executable_semantics/ast:expression",
         "//executable_semantics/ast:paren_contents",

executable_semantics/syntax/lexer.lpp

@@ -30,6 +30,7 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 /* Table begin. */
 AND                  "and"
+API                  "api"
 ARROW                "->"
 AUTO                 "auto"
 AWAIT                "__await"
@@ -53,13 +54,17 @@ FALSE                "false"
 FN                   "fn"
 FNTY                 "fnty"
 IF                   "if"
+IMPL                 "impl"
+IMPORT               "import"
 LEFT_CURLY_BRACE     "{"
 LEFT_PARENTHESIS     "("
 LEFT_SQUARE_BRACKET  "["
+LIBRARY              "library"
 MATCH                "match"
 MINUS                "-"
 NOT                  "not"
 OR                   "or"
+PACKAGE              "package"
 PERIOD               "."
 PLUS                 "+"
 RETURN               "return"
@@ -119,6 +124,7 @@ string_literal        \"([^\\\"\n\v\f\r]|\\.)*\"
 
  /* Table begin. */
 {AND}                 { return SIMPLE_TOKEN(AND);                 }
+{API}                 { return SIMPLE_TOKEN(API);                 }
 {ARROW}               { return SIMPLE_TOKEN(ARROW);               }
 {AUTO}                { return SIMPLE_TOKEN(AUTO);                }
 {AWAIT}               { return SIMPLE_TOKEN(AWAIT);               }
@@ -142,13 +148,17 @@ string_literal        \"([^\\\"\n\v\f\r]|\\.)*\"
 {FNTY}                { return SIMPLE_TOKEN(FNTY);                }
 {FN}                  { return SIMPLE_TOKEN(FN);                  }
 {IF}                  { return SIMPLE_TOKEN(IF);                  }
+{IMPL}                { return SIMPLE_TOKEN(IMPL);                }
+{IMPORT}              { return SIMPLE_TOKEN(IMPORT);              }
 {LEFT_PARENTHESIS}    { return SIMPLE_TOKEN(LEFT_PARENTHESIS);    }
 {LEFT_CURLY_BRACE}    { return SIMPLE_TOKEN(LEFT_CURLY_BRACE);    }
 {LEFT_SQUARE_BRACKET} { return SIMPLE_TOKEN(LEFT_SQUARE_BRACKET); }
+{LIBRARY}             { return SIMPLE_TOKEN(LIBRARY);             }
 {MATCH}               { return SIMPLE_TOKEN(MATCH);               }
 {MINUS}               { return SIMPLE_TOKEN(MINUS);               }
 {NOT}                 { return SIMPLE_TOKEN(NOT);                 }
 {OR}                  { return SIMPLE_TOKEN(OR);                  }
+{PACKAGE}             { return SIMPLE_TOKEN(PACKAGE);             }
 {PERIOD}              { return SIMPLE_TOKEN(PERIOD);              }
 {PLUS}                { return SIMPLE_TOKEN(PLUS);                }
 {RETURN}              { return SIMPLE_TOKEN(RETURN);              }

executable_semantics/syntax/parse.h

@@ -8,7 +8,7 @@
 #include <string>
 #include <variant>
 
-#include "executable_semantics/ast/abstract_syntax_tree.h"
+#include "executable_semantics/ast/ast.h"
 
 namespace Carbon {
 

executable_semantics/syntax/parse_and_lex_context.h

@@ -7,7 +7,7 @@
 
 #include <variant>
 
-#include "executable_semantics/ast/abstract_syntax_tree.h"
+#include "executable_semantics/ast/ast.h"
 #include "executable_semantics/syntax/parser.h"  // from parser.ypp
 
 namespace Carbon {

executable_semantics/syntax/parser.ypp

@@ -65,7 +65,7 @@
 %code requires {
   #include <optional>
 
-  #include "executable_semantics/ast/abstract_syntax_tree.h"
+  #include "executable_semantics/ast/ast.h"
   #include "executable_semantics/ast/declaration.h"
   #include "executable_semantics/ast/expression.h"
   #include "executable_semantics/ast/function_definition.h"
@@ -93,6 +93,11 @@
 %token <std::string> sized_type_literal
 %token <std::string> string_literal
 %type <std::string> designator
+%type <std::pair<LibraryName, bool>> package_directive
+%type <LibraryName> import_directive
+%type <std::vector<LibraryName>> import_directives
+%type <std::string> optional_library_path
+%type <bool> api_or_impl
 %type <BisonWrap<Ptr<const Declaration>>> declaration
 %type <BisonWrap<Ptr<const FunctionDefinition>>> function_declaration
 %type <BisonWrap<Ptr<const FunctionDefinition>>> function_definition
@@ -133,6 +138,7 @@
 %token
   // Most tokens have their spelling defined in lexer.lpp.
   AND
+  API
   ARROW
   AUTO
   AWAIT
@@ -156,13 +162,17 @@
   FN
   FNTY
   IF
+  IMPL
+  IMPORT
   LEFT_CURLY_BRACE
   LEFT_PARENTHESIS
   LEFT_SQUARE_BRACKET
+  LIBRARY
   MATCH
   MINUS
   NOT
   OR
+  PACKAGE
   PERIOD
   PLUS
   RETURN
@@ -217,8 +227,42 @@
 
 %start input
 %%
-input: declaration_list
-    { parsed_program = $1; }
+input: package_directive import_directives declaration_list
+    {
+      parsed_program = AST({.package = $1.first,
+                            .is_api = $1.second,
+                            .imports = std::move($2),
+                            .declarations = std::move($3)});
+    }
+;
+package_directive:
+  PACKAGE identifier optional_library_path api_or_impl SEMICOLON
+    { $$ = {LibraryName({.package = $2, .path = $3}), $4}; }
+;
+import_directive:
+  IMPORT identifier optional_library_path SEMICOLON
+    { $$ = LibraryName({.package = $2, .path = $3}); }
+;
+import_directives:
+  // Empty
+    { $$ = std::vector<LibraryName>(); }
+| import_directives import_directive
+    {
+      $$ = std::move($1);
+      $$.push_back($2);
+    }
+;
+optional_library_path:
+  // Empty
+    { $$ = ""; }
+| LIBRARY string_literal
+    { $$ = $2; }
+;
+api_or_impl:
+  API
+    { $$ = true; }
+| IMPL
+    { $$ = false; }
 ;
 expression:
   identifier