initial checkin of SkSL compiler

src/sksl/ast/SkSLASTForStatement.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+ 
+#ifndef SKSL_ASTFORSTATEMENT
+#define SKSL_ASTFORSTATEMENT
+
+#include "SkSLASTStatement.h"
+
+namespace SkSL {
+
+/**
+ * A 'for' loop. 
+ */
+struct ASTForStatement : public ASTStatement {
+    ASTForStatement(Position position, std::unique_ptr<ASTStatement> initializer, 
+                   std::unique_ptr<ASTExpression> test, std::unique_ptr<ASTExpression> next,

[dogben, 2016/06/20 16:23:18]

Should next be a statement?

[ethannicholas, 2016/06/20 17:45:49]

This is for the third entry in a for loop ('for (int i = 0; i < 10; i++)'); only
expressions are legal there.

[mtklein, 2016/06/20 18:25:25]

It helps me to remember that many things you think of as statements (like
assignment) are actually expressions.  IIRC, the for-loop grammar just allows
two forms, with a special case for starting with a declaration:
   for (expr; expr; expr)
   for (decl; expr; expr)

[dogben, 2016/06/20 18:26:26]

Ok, I see that in the parser, e.g. "i += 2" becomes an ASTExpression rather than
an ASTStatement.

+                   std::unique_ptr<ASTStatement> statement)
+    : INHERITED(position, kFor_Kind)
+    , fInitializer(std::move(initializer))
+    , fTest(std::move(test))
+    , fNext(std::move(next))
+    , fStatement(std::move(statement)) {}
+
+    std::string description() const override {
+        std::string result = std::string("for (");

[dogben, 2016/06/20 16:23:18]

uber-nit: "std::string(" unnecessary

+        if (fInitializer) {
+            result.append(fInitializer->description());

[dogben, 2016/06/20 16:23:18]

uber-nit: elsewhere in this CL, you use += rather than .append.

+        }
+        result.append(" ");

[dogben, 2016/06/20 16:23:18]

;

+        if (fTest) {
+            result.append(fTest->description());
+        }
+        result.append("; ");
+        if (fNext) {
+            result.append(fNext->description());
+        }
+        return result + ") " + fStatement->description();        

[dogben, 2016/06/20 16:23:18]

nit: Is the compiler smart enough to append to result and return it, or does
this make a copy of result?

(Same comment in other files.)

+    }
+
+    const std::unique_ptr<ASTStatement> fInitializer;
+    const std::unique_ptr<ASTExpression> fTest;
+    const std::unique_ptr<ASTExpression> fNext;
+    const std::unique_ptr<ASTStatement> fStatement;
+
+    typedef ASTStatement INHERITED;
+};
+
+} // namespace
+
+#endif