Fix URISyntaxException in MavenPomDownloader for unresolved version placeholders (#7313)

* Fix URISyntaxException in MavenPomDownloader for unresolved property placeholders

When a parent POM version contains unresolved placeholders like ${revision}
and the parent isn't found locally, the download method would construct a URI
with illegal { } characters, causing URISyntaxException. Added an early check
to throw MavenDownloadingException instead, which callers already handle
gracefully by falling through to property resolution.

* Apply suggestion from @timtebeek

Author: timtebeek

rewrite-maven/src/main/java/org/openrewrite/maven/internal/MavenPomDownloader.java

@@ -558,6 +558,12 @@ public Pom download(GroupArtifactVersion gav,
         gav = resolveNamedVersion(gav, containingPom, repositories, ctx);
         String versionMaybeDatedSnapshot = datedSnapshotVersion(gav, containingPom, repositories, ctx);
         gav = handleSnapshotTimestampVersion(gav);
+
+        if (gav.getVersion().contains("${")) {
+            throw new MavenDownloadingException("Unable to download POM " + gav +
+                    ". Version contains unresolved property placeholder.", null, originalGav);
+        }
+
         Iterable<MavenRepository> normalizedRepos = distinctNormalizedRepositories(repositories, containingPom, gav.getVersion());
 
         Timer.Sample sample = Timer.start();

rewrite-maven/src/test/java/org/openrewrite/maven/internal/MavenPomDownloaderTest.java

@@ -1108,7 +1108,7 @@ void shouldThrowExceptionForModulesInModulesWithNoRightProperty() {
 
             var downloader = new MavenPomDownloader(pomsByPath, ctx);
 
-            assertThrows(IllegalArgumentException.class, () -> downloader.download(gav, Objects.requireNonNull(pom.getParent()).getRelativePath(), resolvedPom, singletonList(nonexistentRepo)));
+            assertThrows(MavenDownloadingException.class, () -> downloader.download(gav, Objects.requireNonNull(pom.getParent()).getRelativePath(), resolvedPom, singletonList(nonexistentRepo)));
         }
 
         @Test
@@ -1197,9 +1197,10 @@ void emptyRelativePathSkipsLocalParentLookup() {
             assertDoesNotThrow(() -> downloader.download(requestedGav, null, resolvedPom, singletonList(nonexistentRepo)));
 
             // With empty relativePath (<relativePath/>), step 3 is skipped entirely.
-            // Since the parent can't be found by GAV match either, and the remote
-            // repo doesn't exist, download fails — proving local lookup was skipped.
-            assertThrows(Exception.class,
+            // Since the parent can't be found by GAV match either, the version still
+            // contains an unresolved placeholder, so download throws MavenDownloadingException
+            // instead of URISyntaxException from URI.create().
+            assertThrows(MavenDownloadingException.class,
               () -> downloader.download(requestedGav, "", resolvedPom, singletonList(nonexistentRepo)));
         }