fix(java): say when a configured JDK path no longer exists (#764)

A JDK path chosen in settings that was later removed (a version manager replacing it on upgrade) was reported as "is not a JDK home", which reads as a wrong folder layout. A missing path is now reported as missing, with how to fix it; the project JDK's log warning uses the same wording.

Fixes #741

crates/ide-sdk/src/apply.rs

@@ -78,7 +78,7 @@ fn jdk_setting(root: &Path, value: &str) -> Option<Result<crate::java::Jdk, Path
 /// The project JDK (`languages.java.jdk`), else the JDK the project pins for mise / asdf.
 pub fn project_jdk(root: &Path, s: &Settings) -> Option<crate::java::Jdk> {
     match jdk_setting(root, &s.languages.java.jdk) {
-        Some(jdk) => jdk.inspect_err(|p| tracing::warn!("project JDK {} is not a JDK home", p.display())).ok(),
+        Some(jdk) => jdk.inspect_err(|p| tracing::warn!("project JDK {}", not_a_jdk(p))).ok(),
         None => pinned::pinned_install(root, Tool::Java).and_then(|(dir, _)| pinned::jdk_in_install(&dir)),
     }
 }
@@ -92,10 +92,19 @@ pub fn jdtls_jdk(root: &Path, s: &Settings) -> Result<Option<crate::java::Jdk>,
             Err(crate::java::server_jdk_incomplete_message(&jdk, jdk.major.max(crate::java::JDTLS_MIN_JAVA)))
         }
         Some(Ok(jdk)) => Ok(Some(jdk)),
-        Some(Err(p)) => Err(format!(
-            "The language server JDK {} is not a JDK home (Settings › Languages & Frameworks › Java).",
-            p.display()
-        )),
+        Some(Err(p)) => {
+            Err(format!("The language server JDK {} (Settings › Languages & Frameworks › Java).", not_a_jdk(&p)))
+        }
+    }
+}
+
+/// Why the configured JDK path `p` is not used: gone (e.g. a version manager removed
+/// it on upgrade) or not a JDK.
+fn not_a_jdk(p: &Path) -> String {
+    if p.exists() {
+        format!("{} is not a JDK home", p.display())
+    } else {
+        format!("{} does not exist; choose another JDK or clear the setting to detect one", p.display())
     }
 }
 

crates/ide-sdk/src/tests.rs

@@ -319,8 +319,13 @@ fn jdtls_jdk_setting() {
     .unwrap();
     assert!(jdtls_jdk(tmp.path(), &s).unwrap_err().contains("full JDK"));
     // A chosen path that is not a JDK is an error, not a silent fallback.
-    s.languages.java.jdtls_jdk = "missing".into();
+    std::fs::create_dir(tmp.path().join("not-a-jdk")).unwrap();
+    s.languages.java.jdtls_jdk = "not-a-jdk".into();
     assert!(jdtls_jdk(tmp.path(), &s).unwrap_err().contains("is not a JDK home"));
+    // A JDK removed after it was chosen (a version manager upgraded it) says so.
+    s.languages.java.jdtls_jdk = "jdk17.0.1".into();
+    let err = jdtls_jdk(tmp.path(), &s).unwrap_err();
+    assert!(err.contains("jdk17.0.1 does not exist") && err.contains("Languages & Frameworks › Java"), "{err}");
 }
 
 #[test]