Add #env syntax extension for plucking strings out of the compilation environment.

Author: graydon

src/comp/front/extenv.rs

@@ -0,0 +1,68 @@
+/*
+ * The compiler code necessary to support the #env extension.  Eventually this
+ * should all get sucked into either the compiler syntax extension plugin
+ * interface.
+ */
+
+import util.common;
+
+import std._str;
+import std._vec;
+import std.option;
+import std.GenericOS;
+
+export expand_syntax_ext;
+
+// FIXME: Need to thread parser through here to handle errors correctly
+fn expand_syntax_ext(parser.parser p,
+                     common.span sp,
+                     vec[@ast.expr] args,
+                     option.t[str] body) -> @ast.expr {
+
+    if (_vec.len[@ast.expr](args) != 1u) {
+        p.err("malformed #env call");
+    }
+
+    auto var = expr_to_str(p, args.(0));
+    auto val = GenericOS.getenv(var);
+    ret make_new_str(sp, val);
+}
+
+// FIXME: duplicate code copied from extfmt.
+
+fn expr_to_str(parser.parser p,
+               @ast.expr expr) -> str {
+    alt (expr.node) {
+        case (ast.expr_lit(?l, _)) {
+            alt (l.node) {
+                case (ast.lit_str(?s)) {
+                    ret s;
+                }
+            }
+        }
+    }
+    p.err("malformed #env call");
+    fail;
+}
+
+fn make_new_lit(common.span sp, ast.lit_ lit) -> @ast.expr {
+    auto sp_lit = @rec(node=lit, span=sp);
+    auto expr = ast.expr_lit(sp_lit, ast.ann_none);
+    ret @rec(node=expr, span=sp);
+}
+
+fn make_new_str(common.span sp, str s) -> @ast.expr {
+    auto lit = ast.lit_str(s);
+    ret make_new_lit(sp, lit);
+}
+
+//
+// Local Variables:
+// mode: rust
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
+//

src/comp/front/parser.rs

@@ -948,6 +948,13 @@ fn expand_syntax_ext(parser p, ast.span sp,
                                     expanded,
                                     ast.ann_none);
 
+        ret newexpr;
+    } else if (_str.eq(extname, "env")) {
+        auto expanded = extenv.expand_syntax_ext(p, sp, args, body);
+        auto newexpr = ast.expr_ext(path, args, body,
+                                    expanded,
+                                    ast.ann_none);
+
         ret newexpr;
     } else {
         p.err("unknown syntax extension");

src/comp/rustc.rc

@@ -24,6 +24,7 @@ mod front {
     mod ast;
     mod creader;
     mod extfmt;
+    mod extenv;
     mod codemap;
     mod lexer;
     mod parser;