From 2acd5cf479a757947733b4e131e76a9d833ecd5e Mon Sep 17 00:00:00 2001
From: l0ng-ai <24760907+l0ng-ai@users.noreply.github.com>
Date: Fri, 13 Nov 2026 22:17:50 +0800
Subject: [PATCH] fix(java): import a Gradle build on a JDK its Gradle runs on
 when no version is declared (#3181)

Without a Project JDK and without a Java version the build declares, the jdtls Gradle import ran on jdtls's own runtime, which an older Gradle cannot run on, so every non-JDK dependency stayed unresolved. When the Gradle version is known, the import now uses the newest installed JDK that Gradle supports; a Project JDK, Gradle JVM or declared toolchain still wins.

Fixes #2681
---
 crates/ide-sdk/src/apply.rs | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/crates/ide-sdk/src/apply.rs b/crates/ide-sdk/src/apply.rs
index 6ddf178c1..12dce10c3 100644
--- a/crates/ide-sdk/src/apply.rs
+++ b/crates/ide-sdk/src/apply.rs
@@ -377,6 +377,11 @@ fn gradle_run_jdk<'a>(
     })
 }
 
+/// The newest installed JDK that Gradle `gradle` runs on.
+fn newest_gradle_jdk(gradle: (u32, u32), installed: &[crate::java::Jdk]) -> Option<&crate::java::Jdk> {
+    installed.iter().filter(|jdk| gradle_supports_java(gradle, jdk.major)).max_by_key(|jdk| jdk.major)
+}
+
 /// Default environment shared by Gradle model builds and Run configurations.
 pub fn gradle_build_env(
     root: &Path,
@@ -493,7 +498,17 @@ pub fn configure_gradle_runtime(cfg: &mut LanguageServerConfig, root: &Path, bui
         .any(|f| build_dir.join(f).is_file());
     let env = if gradle_build {
         let command = gradle_command(root, build_dir, s);
-        gradle_build_env(root, build_dir, &command.to_string_lossy(), s, None)
+        let command = command.to_string_lossy();
+        let mut env = gradle_build_env(root, build_dir, &command, s, None);
+        // No Project JDK and no Java version the build declares: jdtls would import on its own
+        // runtime, which an older Gradle cannot run on. Use an installed JDK this Gradle supports.
+        if !env.contains_key("JAVA_HOME")
+            && let Some(gradle) = gradle_distribution_version(build_dir, &command)
+            && let Some(jdk) = newest_gradle_jdk(gradle, &crate::java::installed_jdks())
+        {
+            env.insert("JAVA_HOME".into(), jdk.home.to_string_lossy().into_owned());
+        }
+        env
     } else {
         gradle_env(root, s, Default::default())
     };
@@ -2028,6 +2043,11 @@ mod gradle_runtime_tests {
         assert_eq!(gradle_run_jdk(Some(21), None, &installed, None).unwrap().major, 21);
         assert_eq!(gradle_run_jdk(Some(19), None, &installed, None).unwrap().major, 21);
         assert!(gradle_run_jdk(None, None, &installed, None).is_none());
+        // The Java import of a build that declares no Java version still needs a JVM its Gradle runs on.
+        assert_eq!(newest_gradle_jdk((8, 4), &installed).unwrap().major, 17);
+        assert_eq!(newest_gradle_jdk((7, 2), &installed).unwrap().major, 11);
+        assert_eq!(newest_gradle_jdk((9, 1), &installed).unwrap().major, 25);
+        assert!(newest_gradle_jdk((9, 0), &installed[4..]).is_none());
     }
 
     #[test]