Fix #2901: VersionRange.toString() doesn't handle >0.0.0

The `VersionRange.toString` method was not ideal and dropping
this rare case. A tiny improvement that was also done in the
process is to give higher priority to `matchesAny` so that
we get a more user-friendly output, given how common it is
(e.g. for `ToolchainRequirement`).

source/dub/dependency.d

@@ -1116,6 +1116,7 @@ public struct VersionRange
 		string r;
 
 		if (this == Invalid) return "no";
+		if (this.matchesAny()) return "*";
 		if (this.isExactVersion() && m_inclusiveA && m_inclusiveB) {
 			// Special "==" case
 			if (m_versA == Version.masterBranch) return "~master";
@@ -1142,9 +1143,12 @@ public struct VersionRange
 			}
 		}
 
-		if (m_versA != Version.minRelease) r = (m_inclusiveA ? ">=" : ">") ~ m_versA.toString();
-		if (m_versB != Version.maxRelease) r ~= (r.length==0 ? "" : " ") ~ (m_inclusiveB ? "<=" : "<") ~ m_versB.toString();
-		if (this.matchesAny()) r = ">=0.0.0";
+		if (m_versA != Version.minRelease || !m_inclusiveA)
+			r = (m_inclusiveA ? ">=" : ">") ~ m_versA.toString();
+		if (m_versB != Version.maxRelease || !m_inclusiveB)
+			r ~= (r.length == 0 ? "" : " ") ~ (m_inclusiveB ? "<=" : "<") ~
+				m_versB.toString();
+
 		return r;
 	}
 
@@ -1241,6 +1245,13 @@ unittest {
 	assert(Version("1.0.0+foo").matches(Version("1.0.0+foo"), VersionMatchMode.strict));
 }
 
+// Erased version specification for dependency, converted to "" instead of ">0.0.0"
+// https://github.com/dlang/dub/issues/2901
+unittest
+{
+    assert(VersionRange.fromString(">0.0.0").toString() == ">0.0.0");
+}
+
 /// Determines whether the given string is a Git hash.
 bool isGitHash(string hash) @nogc nothrow pure @safe
 {

test/5-convert/dub.sdl

@@ -7,7 +7,7 @@ copyright "Copyright © 2015, nobody"
 license "BSD 2-clause"
 x:ddoxFilterArgs "dfa1" "dfa2"
 x:ddoxTool "ddoxtool"
-dependency "describe-dependency-1:sub1" version=">=0.0.0"
+dependency "describe-dependency-1:sub1" version="*"
 targetType "sourceLibrary"
 subConfiguration "describe-dependency-1:sub1" "library"
 dflags "--another-dflag"