Dependency version SNAPSHOT is not recognized as snapshot version

[floscher]

Expected Behavior

When I specify a dependency as

repositories {
  maven {
    url "https://example.org/maven"
  }
}
dependencies {
  implementation "org.example:myapp:SNAPSHOT"
}

I expect that Gradle downloads the latest snapshot from the given Maven repo.

The URL of the downloaded artifact might look something like this:
https://example.org/maven/org/example/myapp/SNAPSHOT/myapp-20180601.010203-123.jar

In the process I'd expect Gradle to consult
https://example.org/maven/org/example/myapp/SNAPSHOT/maven-metadata.xml
to find the latest version.

Current Behavior

Gradle fails with the following message:

   > Could not find org.example:myapp:SNAPSHOT.
     Searched in the following locations:
         https://example.org/maven/org/example/myapp/SNAPSHOT/myapp-SNAPSHOT.pom
         https://example.org/maven/org/example/myapp/SNAPSHOT/myapp-SNAPSHOT.jar

Gradle does not recognize that SNAPSHOT is a snapshot version (like 1.0-SNAPSHOT). It treats this version number like a "normal" version number (like 1.2.3).

I played around a bit with this and Gradle seems to only treat versions matching (.+)-SNAPSHOT as such snapshot versions, but https://maven.apache.org/glossary.html clearly states that SNAPSHOT without anything else should also be treated as a snapshot version.

Context

I tried using the following repository in one of my builds: https://josm.openstreetmap.de/nexus/content/repositories/snapshots/

When adding the dependency org.openstreetmap.josm:josm:SNAPSHOT, Gradle errors out because it can't find the dependency.

Steps to Reproduce (for bugs)

See "current behaviour". Add such a dependency and run e.g. ./gradlew dependencies. Under "context" you'll find an example dependency.

[floscher]

This is the line that causes the problem:

gradle/subprojects/dependency-management/src/main/java/org/gradle/api/internal/artifacts/repositories/resolver/MavenResolver.java

Line 267 in ed8edd8

return moduleComponentIdentifier.getVersion().endsWith("-SNAPSHOT");

This should fix the issue:

diff --git a/subprojects/dependency-management/src/main/java/org/gradle/api/internal/artifacts/repositories/resolver/MavenResolver.java b/subprojects/dependency-management/src/main/java/org/gradle/api/internal/artifacts/repositories/resolver/MavenResolver.java
index 62d5114b811..ae10e82473b 100644
--- a/subprojects/dependency-management/src/main/java/org/gradle/api/internal/artifacts/repositories/resolver/MavenResolver.java
+++ b/subprojects/dependency-management/src/main/java/org/gradle/api/internal/artifacts/repositories/resolver/MavenResolver.java
@@ -264,7 +264,7 @@ public class MavenResolver extends ExternalResourceResolver<MavenModuleResolveMe
     }
 
     protected static boolean isNonUniqueSnapshot(ModuleComponentIdentifier moduleComponentIdentifier) {
-        return moduleComponentIdentifier.getVersion().endsWith("-SNAPSHOT");
+        return moduleComponentIdentifier.getVersion().endsWith("-SNAPSHOT") || "SNAPSHOT".equals(moduleComponentIdentifier.getVersion());
     }
 
     private MavenUniqueSnapshotComponentIdentifier composeSnapshotIdentifier(ModuleComponentIdentifier moduleComponentIdentifier, MavenUniqueSnapshotModuleSource uniqueSnapshotVersion) {

Maybe it needs some additonal work, but the main cause should be removed.

[ljacomet]

Thanks for the report.

This issue seems very specific to Maven corner case. We have no bandwidth to work on it for now.
However feel free to submit a pull request fixing this problem, which will need proper test coverage.

[angeloudy]

@floscher Did you find a workaround to this problem?

[floscher]

@angeloudy No I didn't find a workaround.

[cldvr]

Like @floscher pointed out, Maven - Glossary clearly states:

The version can either be the string SNAPSHOT itself, indicating “the very latest” development version, or something like 1.1-SNAPSHOT...

This particular use case is not very common and it's not well documented, but it's perfectly valid. Having a quick look to Maven sources, one can find implementation details in several places specifically to support this use case, so it's not accidental!

My minimal pull request fixes this issue, improving Gradle's compatibility with Maven.

Nevertheless, experimenting with a couple demo projects with real dependencies, one difference remains...

Maven dependencies resolution:

$ mvn -V dependency:resolve
Apache Maven 3.6.3 (cecedd343002696d0abb50b32b541b8a6ba2883f)
...
[INFO] --- maven-dependency-plugin:2.8:resolve (default-cli) @ maven-demo ---
[INFO] 
[INFO] The following files have been resolved:
[INFO]    org.slf4j:slf4j-api:jar:2.0.0-alpha1:compile
[INFO]    org.apache.logging.log4j:log4j-api:jar:3.0.0-SNAPSHOT:compile
[INFO]    org.openstreetmap.josm:josm:jar:20200310.023250-1430:compile

Gradle dependencies resolution:

$ gradle -v
Gradle 6.3-20200302003000+0000

$ gradle -q dependencies --configuration default
...
default - Configuration for default artifacts.
+--- org.slf4j:slf4j-api:2.0.0-alpha1
+--- org.apache.logging.log4j:log4j-api:3.0.0-SNAPSHOT
\--- org.openstreetmap.josm:josm:SNAPSHOT

As you can see above with the josm dependency, Maven replaces SNAPSHOT with the corresponding timestamp while Gradle does not. This is just a display discrepancy, since both tools properly handle the internal conversion. I reckon that Gradle display is better, more coherent when using SNAPSHOT for both log4j-api and josm.

[natario1]

Any plan for fixing this?

[ljacomet]

There is no plan to fix this from the Gradle core team as this does not seem widely used.
The PR proposed was lacking test coverage to be merged.

If someone feels like picking this up, please take a look at the existing PR and make sure test coverage is added. We can then re-open this issue.