Make (install #head?) question more accurate.

src/nimble.nim

@@ -667,7 +667,8 @@ proc install(packages: seq[PkgTuple],
       except BuildFailed:
         # The package failed to build.
         # Check if we tried building a tagged version of the package.
-        if pv.ver.kind != verSpecial:
+        let headVer = parseVersionRange("#" & getHeadName(meth))
+        if pv.ver.kind != verSpecial and downloadVersion != headVer:
           # If we tried building a tagged version of the package then
           # ask the user whether they want to try building #head.
           let promptResult = doPrompt and
@@ -675,8 +676,8 @@ proc install(packages: seq[PkgTuple],
                   " like to try installing '$1@#head' (latest unstable)?") %
                   [pv.name, $downloadVersion])
           if promptResult:
-            let verRange = parseVersionRange("#" & getHeadName(meth))
-            result = install(@[(pv.name, verRange)], options, doPrompt)
+
+            result = install(@[(pv.name, headVer)], options, doPrompt)
           else:
             raise newException(BuildFailed,
               "Aborting installation due to build failure")

src/nimblepkg/version.nim

@@ -80,6 +80,17 @@ proc `==`*(spe: Special, spe2: Special): bool =
 proc `<=`*(ver: Version, ver2: Version): bool =
   return (ver == ver2) or (ver < ver2)
 
+proc `==`*(range1: VersionRange, range2: VersionRange): bool =
+  if range1.kind != range2.kind : return false
+  result = case range1.kind
+  of verLater, verEarlier, verEqLater, verEqEarlier, verEq:
+    range1.ver == range2.ver
+  of verSpecial:
+    range1.spe == range2.spe
+  of verIntersect:
+    range1.verILeft == range2.verILeft and range1.verIRight == range2.verIRight
+  of verAny: true
+
 proc withinRange*(ver: Version, ran: VersionRange): bool =
   case ran.kind
   of verLater: