Add a genrule for cup (#442)

* Add a genrule for cup
  - Update readme for cup
  - Fix sample

cup/BUILD

@@ -2,6 +2,15 @@ package(default_visibility = ["//visibility:public"])
 
 licenses(["notice"])  # GPL-compatible
 
+java_binary(
+    name = "cup_bin",
+    main_class = "java_cup.Main",
+    runtime_deps = [
+        ":cup",
+        ":cup_runtime",
+    ],
+)
+
 java_import(
     name = "cup",
     jars = ["cup/target/cup-11b.jar"],

cup/README.md

@@ -11,4 +11,15 @@ Home directory and parent POM of 2 artefacts:
 Note that this code is excluded from many rules of our codebase,
 for instance google-java-format is not applied.
 
+
+## Bazel rule
+
+    load("//cup:cup.bzl", "cup")
+
+    cup(
+      name = "rule_name",
+      src = "spec.cup",
+     )
+
+
 [cup]: http://www2.cs.tum.edu/projects/cup/

cup/cup.bzl

@@ -0,0 +1,24 @@
+"""Bazel rules for cup. """
+
+# CUP can only read from stdin, which Skylark rules don't support. Use a genrule for now.
+def cup(name, src, parser = "Parser", symbols = "Symbols", interface = False):
+    """Generate a parser with CUP.
+
+    Args:
+      name: name of the rule
+      srcs: list of cup specifications
+      parser: name of the generated parser class
+      symbols: name of the generated symbols class
+      interface: whether to generate an interface
+    """
+    opts = "-parser {parser} -symbols {symbols}".format(parser = parser, symbols = symbols)
+    if interface:
+        opts = opts + " -interface"
+    cmd = ("$(location //cup:cup_bin) -destdir $(@D) " + opts + " < $<")
+    native.genrule(
+        name = name,
+        srcs = [src],
+        tools = ["//cup:cup_bin"],
+        outs = [parser + ".java", symbols + ".java"],
+        cmd = cmd,
+    )

cup/sample-project/BUILD

@@ -0,0 +1,6 @@
+load("//cup:cup.bzl", "cup")
+
+cup(
+    name = "gen_parser",
+    src = "src/main/cup/calculator.cup",
+)