3 files changed, 40 insertions, 6 deletions

diff --git a/src/comp/front/extfmt.rs b/src/comp/front/extfmt.rs
index 3aa24a90..c05c74d1 100644
--- a/src/comp/front/extfmt.rs
+++ b/src/comp/front/extfmt.rs
@@ -29,7 +29,7 @@ import std.ExtFmt.CT.flag;
 import std.ExtFmt.CT.flag_left_justify;
 import std.ExtFmt.CT.flag_left_zero_pad;
 import std.ExtFmt.CT.flag_left_space_pad;
-import std.ExtFmt.CT.flag_plus_if_positive;
+import std.ExtFmt.CT.flag_sign_always;
 import std.ExtFmt.CT.flag_alternate;
 import std.ExtFmt.CT.count;
 import std.ExtFmt.CT.count_is;
@@ -176,6 +176,10 @@ fn pieces_to_expr(vec[piece] pieces, vec[@ast.expr] args) -> @ast.expr {
                         auto fstr = "flag_left_justify";
                         flagexprs += vec(make_rt_path_expr(sp, fstr));
                     }
+                    case (flag_sign_always) {
+                        auto fstr = "flag_sign_always";
+                        flagexprs += vec(make_rt_path_expr(sp, fstr));
+                    }
                 }
             }
 
@@ -279,6 +283,26 @@ fn pieces_to_expr(vec[piece] pieces, vec[@ast.expr] args) -> @ast.expr {
             alt (f) {
                 case (flag_left_justify) {
                 }
+                case (flag_sign_always) {
+                    auto err = "+ flag only valid in signed #fmt conversions";
+                    alt (cnv.ty) {
+                        case (ty_int(?s)) {
+                            alt (s) {
+                                case (signed) {
+                                    // Valid
+                                }
+                                case (unsigned) {
+                                    log err;
+                                    fail;
+                                }
+                            }
+                        }
+                        case (_) {
+                            log err;
+                            fail;
+                        }
+                    }
+                }
                 case (_) {
                     log unsupported;
                     fail;
@@ -361,8 +385,8 @@ fn pieces_to_expr(vec[piece] pieces, vec[@ast.expr] args) -> @ast.expr {
                 case (flag_left_space_pad) {
                     log "flag: left space pad";
                 }
-                case (flag_plus_if_positive) {
-                    log "flag: plus if positive";
+                case (flag_sign_always) {
+                    log "flag: sign always";
                 }
                 case (flag_alternate) {
                     log "flag: alternate";
diff --git a/src/lib/ExtFmt.rs b/src/lib/ExtFmt.rs
index 4be03858..c2cce279 100644
--- a/src/lib/ExtFmt.rs
+++ b/src/lib/ExtFmt.rs
@@ -53,7 +53,7 @@ mod CT {
         flag_left_justify;
         flag_left_zero_pad;
         flag_left_space_pad;
-        flag_plus_if_positive;
+        flag_sign_always;
         flag_alternate;
     }
 
@@ -203,7 +203,7 @@ mod CT {
         } else if (f == (' ' as u8)) {
             ret more(flag_left_space_pad);
         } else if (f == ('+' as u8)) {
-            ret more(flag_plus_if_positive);
+            ret more(flag_sign_always);
         } else if (f == ('#' as u8)) {
             ret more(flag_alternate);
         } else {
@@ -306,6 +306,7 @@ mod RT {
 
     tag flag {
         flag_left_justify;
+        flag_sign_always;
         // FIXME: This is a hack to avoid creating 0-length vec exprs,
         // which have some difficulty typechecking currently. See
         // comments in front.extfmt.make_flags
@@ -334,7 +335,11 @@ mod RT {
     fn conv_int(&conv cv, int i) -> str {
         auto radix = 10u;
         auto prec = get_int_precision(cv);
-        ret pad(cv, int_to_str_prec(i, radix, prec));
+        auto s = int_to_str_prec(i, radix, prec);
+        if (0 <= i && have_flag(cv.flags, flag_sign_always)) {
+            s = "+" + s;
+        }
+        ret pad(cv, s);
     }
 
     fn conv_uint(&conv cv, uint u) -> str {
diff --git a/src/test/run-pass/syntax-extension-fmt.rs b/src/test/run-pass/syntax-extension-fmt.rs
index 5c66b17a..1e283c2d 100644
--- a/src/test/run-pass/syntax-extension-fmt.rs
+++ b/src/test/run-pass/syntax-extension-fmt.rs
@@ -112,4 +112,9 @@ fn main() {
   test(#fmt("%.b", true), "");
   test(#fmt("%.0b", true), "");
   test(#fmt("%.1b", true), "t");
+
+  // Explicit + sign. Only for signed conversions
+  test(#fmt("%+d", 0), "+0");
+  test(#fmt("%+d", 1), "+1");
+  test(#fmt("%+d", -1), "-1");
 }