Fix bug that drops srcloc on withUnit calls

Author: BenMusch

src/arr/trove/error.arr

@@ -2459,12 +2459,10 @@ data RuntimeError:
         self.render-reason()
       end
     end,
-    method render-reason(self):
+    method render-reason(self) block:
       base-err = [ED.para:
         ed-simple-intro("unit annotation", self.loc),
-        ED.text("The annotation at "),
-        ED.loc(self.loc),
-        ED.text(" is annotated with the unit "),
+        ED.text("The annotation is annotated with the unit "),
         ED.code(ED.text(self.unit-str)),
         ED.text(" but does not support unit annotations.")]
       if self.loc.is-builtin():

src/js/base/runtime.js

@@ -2935,15 +2935,15 @@ function (Namespace, jsnums, codePoint, util, exnStackParser, loader, seedrandom
     }
     function makeUnitAnn(ann, u, srcloc) {
       if (ann.withUnit === undefined) {
-        thisRuntime.ffi.throwUnitsOnUnsupportedAnn(jsnums.unitToString(u), makeSrcloc(srcloc));
+        thisRuntime.ffi.throwUnitsOnUnsupportedAnn(jsnums.unitToString(u), srcloc);
       }
-      return ann.withUnit(u);
+      return ann.withUnit(u, srcloc);
     }
     PUnitAnn.prototype.withUnit = function(unit, srcloc) {
       if (this.implicit || jsnums.checkUnit(this.u, unit)) {
         return new PUnitAnn(this.ann, unit, false);
       } else {
-        thisRuntime.ffi.throwUnitsOnUnsupportedAnn(jsnums.unitToString(unit), makeSrcloc(srcloc));
+        thisRuntime.ffi.throwUnitsOnUnsupportedAnn(jsnums.unitToString(unit), srcloc);
       }
     }
     PUnitAnn.prototype.check = function(compilerLoc, val) {

src/js/trove/ffi.js

@@ -500,6 +500,7 @@
       raise(makeModuleLoadFailureL(names));
     }
     function throwUnitsOnUnsupportedAnn(unitStr, loc) {
+      loc = runtime.makeSrcloc(loc);
       runtime.checkString(unitStr);
       raise(err("units-on-unsupported-ann")(loc, unitStr));
     }