feat(java): open class files as decompiled sources with breakpoints (#657)

Opening a .class file showed binary content. Class files from library jars, project output directories, navigation, Go to Class and debugger frames now all go through one route to JDT class documents:

- Library classes open the attached source, or the FernFlower decompilation when there is none, read-only and marked as decompiled. java-debug's decompiled-source support is enabled, so breakpoints set in decompiled code map to the original lines and hit, and stepping into such classes lands on the right line.
- Output-directory classes (target/classes, build/classes) open their project source when it exists; otherwise the decompiled text is shown read-only with breakpoints disabled, because jdt.ls returns no line mapping for classes outside the Java model.
- The preferred content provider id is corrected to fernflowerContentProvider (attached sources still win), and the decompiled marker recognises the current FernFlower header.

Verified on macOS with a Maven project: library class from Libraries and Go to Class, breakpoint hit and step into decompiled code, output class with and without source. Not run on Windows, Linux or Gradle projects.

Fixes #394

crates/ide-host/src/ops/lsp.rs

@@ -83,12 +83,18 @@ pub async fn lsp_implementations(
     result
 }
 
-/// Contents of a virtual document (library class, decompiled code) that a
-/// language server returned a non-`file:` URI for. Cached per project.
+/// Contents of a read-only language-server document, including JDT library
+/// classes and disk class files. Cached per project.
 pub async fn lsp_virtual_document(host: &Host, window: &str, uri: String) -> IdeResult<VirtualDocument> {
     host.project(window)?.lsp.virtual_document(&uri).await
 }
 
+/// Opens compiled classes through JDT, with project source taking priority on disk.
+pub async fn lsp_resolve_class_file(host: &Host, window: &str, path: std::path::PathBuf) -> IdeResult<String> {
+    let archive = ide_vfs::split_archive_path(&path);
+    host.project(window)?.lsp.java_class_file(&path, archive).await
+}
+
 /// References of the symbol at `pos`. `project_wide` also searches project files
 /// outside the language server's analysis scope; bulk scans over many symbols
 /// leave it off. Cancel with `cancel_request(request)`.
@@ -367,6 +373,10 @@ pub(crate) fn register(d: &mut Dispatcher) {
     d.add("lsp_implementations", |c| async move {
         lsp_implementations(&c.host, &c.window, c.arg("request")?, c.arg("doc")?, c.arg("positions")?).await
     });
+    d.add(
+        "lsp_resolve_class_file",
+        |c| async move { lsp_resolve_class_file(&c.host, &c.window, c.arg("path")?).await },
+    );
     d.add("lsp_virtual_document", |c| async move { lsp_virtual_document(&c.host, &c.window, c.arg("uri")?).await });
     d.add("lsp_references", |c| async move {
         lsp_references(

crates/ide-lsp/src/jdtls.rs

@@ -532,6 +532,59 @@ impl LspManager {
         collect()
     }
 
+    /// Resolve a disk/archive class to project source or the server's binary document.
+    /// Archive URIs must come from JDT's Java model: fabricated handles cannot map debug lines.
+    pub async fn java_class_file(&self, path: &Path, archive: Option<(PathBuf, String)>) -> IdeResult<String> {
+        let cancel = CancellationToken::new();
+        self.jdtls(&self.project_root, &cancel).await?;
+        if let Some((jar, entry)) = archive {
+            let entry = entry
+                .strip_prefix("META-INF/versions/")
+                .and_then(|s| s.split_once('/').map(|(_, s)| s))
+                .unwrap_or(&entry);
+            let class = entry.strip_suffix(".class").ok_or_else(|| IdeError::not_found("expected a class file"))?;
+            let outer = class.split('$').next().unwrap_or(class);
+            let (package, name) = outer.rsplit_once('/').unwrap_or(("", outer));
+            let query = outer.replace('/', ".");
+            let symbols = self.workspace_symbols(&query, cancel).await?;
+            let package = package.replace('/', ".");
+            let name = name.to_owned();
+            let outer = outer.to_owned();
+            return tokio::task::spawn_blocking(move || {
+                symbols
+                    .into_iter()
+                    .filter_map(|s| s.location.uri)
+                    .find(|uri| crate::virtual_doc::matches_class(uri, &jar, &package, &name))
+                    .ok_or_else(|| {
+                        IdeError::not_found(format!("jdtls could not resolve {} in {}", outer, jar.display()))
+                    })
+            })
+            .await
+            .map_err(|e| IdeError::internal(e.to_string()))?;
+        }
+        let uri = crate::uri::path_to_uri_string(path);
+        // classFileContents accepts file URIs, but java-debug's line mapping only accepts JDT handles.
+        let doc = self.virtual_document(&uri).await?;
+        let name = path.file_stem().and_then(|s| s.to_str()).unwrap_or("").split('$').next().unwrap_or("");
+        let package = doc
+            .text
+            .lines()
+            .find_map(|l| l.trim().strip_prefix("package ").and_then(|p| p.strip_suffix(';')))
+            .unwrap_or("");
+        let relative = PathBuf::from(package.replace('.', "/")).join(format!("{name}.java"));
+        let key = "org.eclipse.jdt.ls.core.sourcePaths";
+        let settings = self
+            .jdtls_project_command(path, "java.project.getSettings", vec![json!(uri), json!([key])], &cancel)
+            .await?;
+        let roots: Vec<PathBuf> =
+            settings[key].as_array().into_iter().flatten().filter_map(Value::as_str).map(PathBuf::from).collect();
+        let source =
+            tokio::task::spawn_blocking(move || roots.into_iter().map(|r| r.join(&relative)).find(|p| p.is_file()))
+                .await
+                .map_err(|e| IdeError::internal(e.to_string()))?;
+        Ok(source.map(|s| s.to_string_lossy().into_owned()).unwrap_or(uri))
+    }
+
     /// Starts (or reuses) java-debug's DAP server inside jdtls and returns its port.
     pub async fn java_debug_server(&self, path: &Path) -> IdeResult<u16> {
         let v = self.jdtls_command(path, "vscode.java.startDebugSession", Vec::new()).await.map_err(|e| {
@@ -542,7 +595,7 @@ impl LspManager {
             }
         })?;
         // Hot code replace after each (auto-)build; errors only cost the feature.
-        let settings = json!({ "hotCodeReplace": "auto", "showStaticVariables": false, "showQualifiedNames": false,
+        let settings = json!({ "debugSupportOnDecompiledSource": "on", "hotCodeReplace": "auto", "showStaticVariables": false, "showQualifiedNames": false,
             "showLogicalStructure": true, "showToString": true, "maxStringLength": 0,
             // java-debug NPEs on a missing level (java.util.logging names).
             "logLevel": "WARNING" });
@@ -574,6 +627,7 @@ mod tests {
         assert_eq!(settings["java"]["project"]["sourcePaths"], json!(["src/main/java", "tests"]));
         assert_eq!(settings["java"]["project"]["referencedLibraries"], json!(["lib/**/*.jar"]));
         assert_eq!(settings["java"]["autobuild"]["enabled"], true);
+        assert_eq!(settings["java"]["contentProvider"]["preferred"], "fernflowerContentProvider");
         assert!(settings.get("bundles").is_none());
         assert!(settings.get("settings").is_none(), "didChangeConfiguration takes java settings directly");
     }

crates/ide-lsp/src/lib.rs

@@ -2166,6 +2166,7 @@ impl LspManager {
             return Ok(d.clone());
         }
         let scheme = virtual_doc::scheme(uri).to_owned();
+        let class_file = scheme == "jdt" || (scheme == "file" && uri.ends_with(".class"));
         let origin = self.origin_server(uri);
         let mut servers: Vec<Arc<Server>> = origin.iter().cloned().collect();
         servers.extend(self.servers.lock().iter().filter(|s| Some(s.id) != origin.as_ref().map(|o| o.id)).cloned());
@@ -2174,7 +2175,7 @@ impl LspManager {
         for t in &targets {
             let languages = t.server.languages();
             let serves_scheme = t.caps().content_schemes().contains(&scheme);
-            let result: IdeResult<Option<String>> = if serves_scheme {
+            let result: IdeResult<Option<String>> = if serves_scheme && !class_file {
                 self.call::<_, Option<Value>>(
                     t,
                     "workspace/textDocumentContent",
@@ -2184,7 +2185,7 @@ impl LspManager {
                 )
                 .await
                 .map(|v| v.and_then(|v| v.get("text").and_then(Value::as_str).map(str::to_owned)))
-            } else if scheme == "jdt" && languages.iter().any(|l| l.as_str() == "java") {
+            } else if class_file && languages.iter().any(|l| l.as_str() == "java") {
                 self.call::<_, Option<String>>(t, "java/classFileContents", json!({ "uri": uri }), None, LONG_TIMEOUT)
                     .await
             } else {

crates/ide-lsp/src/types.rs

@@ -335,7 +335,7 @@ pub struct VirtualDocument {
     pub title: String,
     /// Origin shown in the tooltip / banner, e.g. the jar path.
     pub description: Option<String>,
-    /// Generated by a decompiler / disassembler rather than real sources.
+    /// Generated Java from a decompiler, rather than real source or a disassembler stub.
     pub decompiled: bool,
 }
 

crates/ide-lsp/src/virtual_doc.rs

@@ -1,21 +1,29 @@
 //! Virtual documents: read-only contents a language server provides for a
-//! non-`file:` URI (library classes from `jdt://`, `workspace/textDocumentContent`).
+//! URI (library classes from `jdt://`, disk classes from `file://`, or
+//! `workspace/textDocumentContent`).
 
 use percent_encoding::percent_decode_str;
 
-/// Markers decompilers / disassemblers put at the top of generated code.
-const GENERATED_MARKERS: [&str; 5] = [
-    "generated by the fernflower decompiler",
-    "failed to get sources",
-    "decompiled with cfr",
-    "decompiled with procyon",
-    "generated by the disassembler",
-];
-
-/// Whether `text` is decompiled / disassembled code rather than real source.
+/// Recognize decompiler headers, without treating disassembler stubs as Java source.
 pub fn is_decompiled(text: &str) -> bool {
-    let head: String = text.chars().take(600).collect::<String>().to_ascii_lowercase();
-    GENERATED_MARKERS.iter().any(|m| head.contains(m))
+    let head: String = text.chars().take(600).collect();
+    head.lines()
+        .take(12)
+        .take_while(|line| {
+            let line = line.trim();
+            line.is_empty() || line.starts_with("//") || line.starts_with("/*") || line.starts_with('*')
+        })
+        .any(|line| {
+            let line = line.trim().trim_start_matches('/').trim_start_matches('*').trim().to_ascii_lowercase();
+            [
+                "source code is unavailable, and was generated by the fernflower decompiler.",
+                "source code is decompiled from a .class file using fernflower decompiler",
+                "decompiled with cfr",
+                "decompiled with procyon",
+            ]
+            .iter()
+            .any(|marker| line.starts_with(marker))
+        })
 }
 
 /// `scheme` of a URI (`jdt` for `jdt://…`).
@@ -34,7 +42,16 @@ fn segments(uri: &str) -> Vec<String> {
 /// Editor tab title: the last path segment; a class file whose real source
 /// was found is shown as `.java` (IDEA: `String.java` vs `String.class`).
 pub fn title(uri: &str, decompiled: bool) -> String {
-    let name = segments(uri).pop().unwrap_or_else(|| uri.to_owned());
+    let mut name = segments(uri).pop().unwrap_or_else(|| uri.to_owned());
+    // Recent jdtls versions use a .java path even for decompiled class handles.
+    if decompiled
+        && scheme(uri) == "jdt"
+        && name.ends_with(".java")
+        && uri.split_once('?').is_some_and(|(_, q)| percent_decode_str(q).decode_utf8_lossy().contains(".class"))
+    {
+        name.truncate(name.len() - 5);
+        name.push_str(".class");
+    }
     match name.strip_suffix(".class") {
         Some(stem) if !decompiled && scheme(uri) == "jdt" => format!("{stem}.java"),
         _ => name,
@@ -68,6 +85,19 @@ pub fn description(uri: &str) -> Option<String> {
     }
 }
 
+/// Check both the package and actual archive, so duplicate type names never pick another jar.
+pub(crate) fn matches_class(uri: &str, jar: &std::path::Path, package: &str, name: &str) -> bool {
+    let segs = segments(uri);
+    scheme(uri) == "jdt"
+        && (package.is_empty() && segs.len() == 3 || segs.get(2).is_some_and(|s| s == package))
+        && segs.last().is_some_and(|s| s == &format!("{name}.class") || s == &format!("{name}.java"))
+        && description(uri).is_some_and(|p| {
+            let path = std::path::Path::new(&p);
+            path == jar
+                || dunce::canonicalize(path).ok().zip(dunce::canonicalize(jar).ok()).is_some_and(|(a, b)| a == b)
+        })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -84,6 +114,30 @@ mod tests {
 
     #[test]
     fn jdt_description() {
+        assert!(matches_class(
+            JDT,
+            std::path::Path::new("/Users/me/.m2/repository/spring-boot-4.1.1.jar"),
+            "org.springframework.boot",
+            "SpringApplication"
+        ));
+        assert!(!matches_class(
+            JDT,
+            std::path::Path::new("/elsewhere/spring-boot-4.1.1.jar"),
+            "org.springframework.boot",
+            "SpringApplication"
+        ));
+        assert!(!matches_class(
+            JDT,
+            std::path::Path::new("/Users/me/.m2/repository/spring-boot-4.1.1.jar"),
+            "other.package",
+            "SpringApplication"
+        ));
+        assert!(matches_class(
+            "jdt://contents/a.jar//C.java?=p/%5C/m2%5C/a.jar%3C%28C.class",
+            std::path::Path::new("/m2/a.jar"),
+            "",
+            "C"
+        ));
         assert_eq!(description(JDT).as_deref(), Some("/Users/me/.m2/repository/spring-boot-4.1.1.jar"));
         assert_eq!(
             description(
@@ -98,10 +152,18 @@ mod tests {
 
     #[test]
     fn detects_generated_code() {
+        assert!(is_decompiled(
+            "// Source code is decompiled from a .class file using FernFlower decompiler (from Intellij IDEA).\npackage a;"
+        ));
+        assert!(!is_decompiled("package a;\n// generated by the fernflower decompiler"));
+        assert!(!is_decompiled("// Documentation about code generated by the Fernflower decompiler.\npackage a;"));
+        let recent = "jdt://contents/a.jar/p/C.java?=p/a.jar%3Cp%28C.class";
+        assert_eq!(title(recent, true), "C.class");
+        assert_eq!(title(recent, false), "C.java");
         assert!(is_decompiled(
             "// Source code is unavailable, and was generated by the Fernflower decompiler.\npackage a;"
         ));
-        assert!(is_decompiled(
+        assert!(!is_decompiled(
             "// Failed to get sources. Instead, stub sources have been generated by the disassembler."
         ));
         assert!(!is_decompiled("/*\n * Copyright 2012-2024 the original author or authors.\n */\npackage a;"));

crates/ide-lsp/tests/mock_server.rs

@@ -1617,6 +1617,58 @@ async fn jdt_class_file_contents() {
     assert_eq!(vd.title, "Lib.class");
     assert_eq!(vd.language_id.as_str(), "java");
     assert_eq!(vd.description.as_deref(), Some("/m2/lib-1.0.jar"));
+    let source_uri = jdt.replace("Lib.class", "WithSources.class");
+    s.respond(
+        "java/classFileContents",
+        json!("/* Copyright library author */\npackage org.example;\npublic class WithSources {}"),
+    );
+    let source = h.mgr.virtual_document(&source_uri).await.unwrap();
+    assert!(!source.decompiled);
+    assert_eq!(source.title, "WithSources.java");
+}
+
+#[tokio::test(flavor = "multi_thread")]
+async fn class_file_opening_routes_sources_and_binary_documents() {
+    let mut caps = incremental_caps();
+    caps["workspaceSymbolProvider"] = json!(true);
+    let h = harness_for("java", "java", &[("jdtls", caps)], &[]);
+    h.open("App.java", "class App {}\n");
+    h.wait_status("jdtls", ServerStatus::Ready).await;
+    let s = h.launcher.state("jdtls");
+    let jdt = "jdt://contents/lib.jar/p/Outer.java?=demo/%5C/m2%5C/lib.jar%3Cp%28Outer.class";
+    s.respond("workspace/symbol", json!([
+        {"name":"Outer", "kind":5, "location":{"uri":jdt,"range":{"start":{"line":0,"character":0},"end":{"line":0,"character":0}}}}
+    ]));
+    let archive = Some((PathBuf::from("/m2/lib.jar"), "p/Outer$1.class".into()));
+    assert_eq!(h.mgr.java_class_file(Path::new("/m2/lib.jar!/p/Outer$1.class"), archive).await.unwrap(), jdt);
+    assert!(
+        h.mgr
+            .java_class_file(
+                Path::new("/other/lib.jar!/p/Outer.class"),
+                Some(("/other/lib.jar".into(), "p/Outer.class".into()))
+            )
+            .await
+            .is_err()
+    );
+
+    let sources = h.root.join("src/main/java");
+    std::fs::create_dir_all(sources.join("p")).unwrap();
+    let source = sources.join("p/Outer.java");
+    std::fs::write(&source, "package p; class Outer {} ").unwrap();
+    s.respond("java/classFileContents", json!("// Source code is decompiled from a .class file using FernFlower decompiler (from Intellij IDEA).\npackage p;\npublic class Outer {}"));
+    s.respond("workspace/executeCommand", json!({"org.eclipse.jdt.ls.core.sourcePaths":[sources]}));
+    for class in ["Outer", "Outer$Nested", "Outer$1"] {
+        let path = h.root.join(format!("target/classes/p/{class}.class"));
+        assert_eq!(h.mgr.java_class_file(&path, None).await.unwrap(), source.to_string_lossy());
+    }
+    let path = h.root.join("build/classes/java/main/p/Missing.class");
+    let uri = uri_of(&path);
+    assert_eq!(h.mgr.java_class_file(&path, None).await.unwrap(), uri);
+    let vd = h.mgr.virtual_document(&uri).await.unwrap();
+    assert!(vd.decompiled);
+    assert_eq!(vd.language_id.as_str(), "java");
+    assert_eq!(vd.title, "Missing.class");
+    assert!(s.requested("java/classFileContents").iter().any(|p| p["uri"] == uri));
 }
 
 #[tokio::test(flavor = "multi_thread")]

crates/ide-sdk/src/libraries.rs

@@ -8,7 +8,7 @@
 //! result is cached until the manifests (or the relevant settings) change.
 //!
 //! Archives are listed as browsable roots (`<archive>!`, see `ide_vfs`): the
-//! JDK's `src.zip` and the Maven / Gradle dependency jars (sources jars preferred).
+//! JDK's `src.zip` and the Maven / Gradle dependency jars (source attachments resolved by JDT).
 
 use crate::exe;
 use crate::exec::{query, query_in, which};
@@ -248,7 +248,7 @@ fn gradle_user_home() -> Option<PathBuf> {
 }
 
 /// One `Maven: g:a:v` / `Gradle: g:a:v` group per dependency whose jar is in a
-/// local repository, its root being the jar (the `-sources.jar` when downloaded).
+/// local repository, its root being the binary jar so Java classes open through JDT's source provider.
 pub(crate) fn dependency_libraries(
     deps: &[BuildDependency],
     maven_repo: Option<&Path>,
@@ -286,7 +286,7 @@ pub(crate) fn maven_jar(repo: &Path, d: &BuildDependency) -> Option<PathBuf> {
         return None;
     }
     let dir = repo.join(d.group.replace('.', "/")).join(&d.artifact).join(&d.version);
-    ["-sources.jar", ".jar"]
+    [".jar", "-sources.jar"]
         .iter()
         .map(|suffix| dir.join(format!("{}-{}{suffix}", d.artifact, d.version)))
         .find(|p| p.is_file())
@@ -300,7 +300,7 @@ pub(crate) fn gradle_jar(home: &Path, d: &BuildDependency) -> Option<PathBuf> {
     let dir = home.join("caches/modules-2/files-2.1").join(&d.group).join(&d.artifact).join(&d.version);
     let mut hashes: Vec<PathBuf> = std::fs::read_dir(dir).ok()?.flatten().map(|e| e.path()).collect();
     hashes.sort();
-    ["-sources.jar", ".jar"].iter().find_map(|suffix| {
+    [".jar", "-sources.jar"].iter().find_map(|suffix| {
         let file = format!("{}-{}{suffix}", d.artifact, d.version);
         hashes.iter().map(|h| h.join(&file)).find(|p| p.is_file())
     })

crates/ide-sdk/src/tests.rs

@@ -540,12 +540,12 @@ fn build_dependencies_resolve_to_local_jars() {
         std::fs::write(&p, "").unwrap();
         p
     };
-    touch(m2.join("com/google/guava/guava/33.0/guava-33.0.jar"));
-    let guava_src = touch(m2.join("com/google/guava/guava/33.0/guava-33.0-sources.jar"));
+    let guava = touch(m2.join("com/google/guava/guava/33.0/guava-33.0.jar"));
+    touch(m2.join("com/google/guava/guava/33.0/guava-33.0-sources.jar"));
     let junit = touch(m2.join("junit/junit/4.13/junit-4.13.jar"));
     let files = gradle.join("caches/modules-2/files-2.1/org.slf4j/slf4j-api/2.0.9");
-    touch(files.join("a1b2/slf4j-api-2.0.9.jar"));
-    let slf4j_src = touch(files.join("c3d4/slf4j-api-2.0.9-sources.jar"));
+    let slf4j = touch(files.join("a1b2/slf4j-api-2.0.9.jar"));
+    touch(files.join("c3d4/slf4j-api-2.0.9-sources.jar"));
     let dep = |gradle: bool, g: &str, a: &str, v: &str| BuildDependency {
         gradle,
         group: g.into(),
@@ -566,14 +566,14 @@ fn build_dependencies_resolve_to_local_jars() {
     assert_eq!(
         shown,
         [
-            ("Maven: com.google.guava:guava:33.0", "maven", "guava-33.0-sources.jar"),
+            ("Maven: com.google.guava:guava:33.0", "maven", "guava-33.0.jar"),
             ("Maven: junit:junit:4.13", "maven", "junit-4.13.jar"),
-            ("Gradle: org.slf4j:slf4j-api:2.0.9", "gradle", "slf4j-api-2.0.9-sources.jar"),
+            ("Gradle: org.slf4j:slf4j-api:2.0.9", "gradle", "slf4j-api-2.0.9.jar"),
         ]
     );
-    assert_eq!(groups[0].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&guava_src)));
+    assert_eq!(groups[0].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&guava)));
     assert_eq!(groups[1].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&junit)));
-    assert_eq!(groups[2].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&slf4j_src)));
+    assert_eq!(groups[2].roots[0].path, ide_core::IpcPath::from(ide_vfs::archive_root(&slf4j)));
     // A Gradle build also finds jars installed in the Maven local repository (`mavenLocal()`).
     let groups = dependency_libraries(&[dep(true, "junit", "junit", "4.13")], Some(&m2), Some(&gradle));
     assert_eq!(groups[0].name, "Gradle: junit:junit:4.13");

languages/java.toml

@@ -32,7 +32,7 @@ resolveAdditionalTextEditsSupport = true
 
 [language-servers.initialization-options.settings.java]
 autobuild = { enabled = true }
-contentProvider = { preferred = "fernflower" }
+contentProvider = { preferred = "fernflowerContentProvider" }
 maven = { downloadSources = true, updateSnapshots = false }
 eclipse = { downloadSources = true }
 references = { includeDecompiledSources = true }

src-tauri/src/commands/lsp.rs

@@ -95,8 +95,8 @@ pub async fn lsp_implementations(
     ide_host::ops::lsp::lsp_implementations(&state.host, window.label(), request, doc, positions).await
 }
 
-/// Contents of a virtual document (library class, decompiled code) that a
-/// language server returned a non-`file:` URI for. Cached per project.
+/// Contents of a read-only language-server document, including JDT library
+/// classes and disk class files. Cached per project.
 #[tauri::command]
 #[specta::specta]
 pub async fn lsp_virtual_document(
@@ -107,6 +107,16 @@ pub async fn lsp_virtual_document(
     ide_host::ops::lsp::lsp_virtual_document(&state.host, window.label(), uri).await
 }
 
+#[tauri::command]
+#[specta::specta]
+pub async fn lsp_resolve_class_file(
+    window: Window,
+    state: State<'_, AppState>,
+    path: std::path::PathBuf,
+) -> IdeResult<String> {
+    ide_host::ops::lsp::lsp_resolve_class_file(&state.host, window.label(), path).await
+}
+
 /// References of the symbol at `pos`. `project_wide` also searches project files
 /// outside the language server's analysis scope; bulk scans over many symbols
 /// leave it off. Cancel with `cancel_request(request)`.

src-tauri/src/commands/mod.rs

@@ -201,6 +201,7 @@ pub fn builder() -> tauri_specta::Builder<tauri::Wry> {
         lsp::lsp_goto,
         lsp::lsp_implementations,
         lsp::lsp_virtual_document,
+        lsp::lsp_resolve_class_file,
         lsp::lsp_references,
         lsp::lsp_document_highlights,
         lsp::lsp_workspace_symbols,

src/bindings.ts

@@ -372,10 +372,11 @@ export const commands = {
 	 */
 	lspImplementations: (request: RequestId, doc: DocId, positions: Pos[]) => typedError<Location[][], IdeError>(__TAURI_INVOKE("lsp_implementations", { request, doc, positions })),
 	/**
-	 *  Contents of a virtual document (library class, decompiled code) that a
-	 *  language server returned a non-`file:` URI for. Cached per project.
+	 *  Contents of a read-only language-server document, including JDT library
+	 *  classes and disk class files. Cached per project.
 	 */
 	lspVirtualDocument: (uri: string) => typedError<VirtualDocument, IdeError>(__TAURI_INVOKE("lsp_virtual_document", { uri })),
+	lspResolveClassFile: (path: string) => typedError<string, IdeError>(__TAURI_INVOKE("lsp_resolve_class_file", { path })),
 	/**
 	 *  References of the symbol at `pos`. `project_wide` also searches project files
 	 *  outside the language server's analysis scope; bulk scans over many symbols
@@ -6310,7 +6311,7 @@ export type VirtualDocument = {
 	title: string,
 	/**  Origin shown in the tooltip / banner, e.g. the jar path. */
 	description: string | null,
-	/**  Generated by a decompiler / disassembler rather than real sources. */
+	/**  Generated Java from a decompiler, rather than real source or a disassembler stub. */
 	decompiled: boolean,
 };
 

src/editor/api.ts

@@ -42,7 +42,7 @@ export interface EditorDocContext {
   /**
    * A read-only virtual document (library class contents from a language
    * server); `path` is then its URI, not a file: skip file-based features
-   * (VCS, local history, TODO scanning, breakpoints…).
+   * (VCS, local history, TODO scanning…). JDT class documents support breakpoints.
    */
   virtual?: boolean;
 }

src/editor/core/backend.ts

@@ -36,7 +36,7 @@ export interface DocPatchedEvent {
 
 export interface DocBackend {
   open(path: string): Promise<DocumentInfo>;
-  /** Opens the read-only virtual document behind a non-`file:` URI (library class contents). */
+  /** Opens a read-only language-server document (library or disk class contents). */
   openVirtual(uri: string): Promise<DocumentInfo>;
   close(doc: DocId): Promise<void>;
   edit(doc: DocId, baseVersion: number, changes: TextChange[]): Promise<number>;

src/editor/core/controller.ts

@@ -89,6 +89,7 @@ import { NavigationHistory } from "./model/navHistory";
 import { EditHistory } from "./model/editHistory";
 import { loadSession, restoreTabsState, serializeSession, storeSession, type FileViewState } from "./model/session";
 import { docBackend, type DocBackend } from "./backend";
+import { isClassFile } from "@/platform/classFiles";
 import { isVirtualUri, virtualDocument } from "@/platform/virtualDocs";
 import type { VirtualDocument } from "@/platform/ipc";
 import type { Scheduler } from "./sync/DocSync";
@@ -860,9 +861,21 @@ export class EditorController implements SlotHost {
       throw new Error("The project is closing");
   }
 
-  async openFile(path: string, o: OpenOptions = {}) {
+  async openFile(path: string, o: OpenOptions = {}): Promise<void> {
     const generation = this.openingGeneration();
     if (isVirtualUri(path)) return this.openVirtual(path, o);
+    if (isClassFile(path)) {
+      await this.projectTransition;
+      this.checkOpening(generation);
+      try {
+        const target = await call(commands.lspResolveClassFile(path));
+        this.checkOpening(generation);
+        return isVirtualUri(target) ? this.openVirtual(target, o) : this.openFile(target, o);
+      } catch (e) {
+        notifications().notify({ level: "warning", title: "Cannot open library class", body: String(e), group: "lsp" });
+        return;
+      }
+    }
     await this.projectTransition;
     this.checkOpening(generation);
     // Images, binary and huge files open in a contributed viewer unless already open as text.
@@ -901,6 +914,7 @@ export class EditorController implements SlotHost {
   }
 
   async openInput(input: EditorInput, o: OpenOptions = {}) {
+    if (input.path && isClassFile(input.path)) return this.openFile(input.path, o);
     return this.admitInput(input, o, this.openingGeneration());
   }
 

src/editor/core/view/Banner.tsx

@@ -3,6 +3,7 @@ import { Icon, T } from "@/ui";
 import { useEditorBanners, type EditorBannerContribution } from "@/workbench/contributions";
 import { useDocMeta } from "../model/document";
 import styles from "./EditorArea.module.css";
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import { tx } from "@/platform/i18n";
 
 const TEXT = {
@@ -28,12 +29,22 @@ export const documentBanner: EditorBannerContribution = {
  * Notice above a library class opened from a language server (IDEA's
  * "Decompiled .class file" / library source bar): read-only, with its origin.
  */
-export function VirtualBanner({ decompiled, description }: { decompiled: boolean; description: string | null }) {
+export function VirtualBanner({
+  decompiled,
+  description,
+  path,
+}: {
+  decompiled: boolean;
+  description: string | null;
+  path: string;
+}) {
+  const reason = classFileBreakpointReason(path);
   return (
     <div className={`${styles.banner} ${styles.libraryBanner}`} role="status">
       <Icon name={decompiled ? "info" : "lock"} size={14} className={styles.bannerIcon} />
-      <span className={styles.bannerText}>
+      <span className={styles.virtualBannerText}>
         {decompiled ? tx("Decompiled .class file: sources are not available.") : tx("Library source (read-only).")}
+        {reason && ` ${tx(reason)}`}
       </span>
       {description && (
         <span className={styles.bannerDetail} title={description}>

src/editor/core/view/EditorArea.module.css

@@ -90,6 +90,10 @@
   background: var(--bg-feedback-warning);
   border-bottom-color: var(--border-feedback-warning);
 }
+.virtualBannerText {
+  min-width: 0;
+  padding: 8px 0;
+}
 .bannerText {
   flex: none;
   white-space: nowrap;

src/editor/core/view/EditorArea.tsx

@@ -398,7 +398,7 @@ function PaneContent({ paneId, tab, tabsVisible }: { paneId: string; tab: Tab; t
     return (
       <>
         {virtual ? (
-          <VirtualBanner decompiled={virtual.decompiled} description={virtual.description} />
+          <VirtualBanner path={tab.input.path!} decompiled={virtual.decompiled} description={virtual.description} />
         ) : (
           <EditorBanners path={tab.input.path} />
         )}

src/editor/core/virtual.test.ts

@@ -10,7 +10,7 @@ vi.mock("@/platform/virtualDocs", async (importOriginal) => {
   return {
     ...actual,
     virtualDocument: vi.fn(async (uri: string): Promise<VirtualDocument> => {
-      if (uri !== JDT) throw new Error(`no contents for ${uri}`);
+      if (uri !== JDT && uri !== "file:///p/target/classes/Lib.class") throw new Error(`no contents for ${uri}`);
       return {
         uri,
         text: TEXT,
@@ -30,6 +30,7 @@ const { serializeSession } = await import("./model/session");
 const { useDocMeta } = await import("./model/document");
 const { registerMenuGroup } = await import("@/workbench/contributions");
 const { registerActions } = await import("@/platform/actions");
+const { commands } = await import("@/platform/ipc");
 const { resolveMenuItems } = await import("@/ui");
 
 let ctrl: InstanceType<typeof EditorController> | null = null;
@@ -55,6 +56,24 @@ describe("virtual editor input", () => {
     expect(isTextInput({ kind: "diff", key: "d" })).toBe(false);
   });
 
+  it.each([
+    ["/m2/lib.jar!/org/example/Lib.class", JDT, "virtual"],
+    ["/p/target/classes/Lib.class", "/p/Lib.java", "file"],
+    ["/p/build/classes/Lib.class", "file:///p/target/classes/Lib.class", "virtual"],
+  ])("routes %s before choosing a binary viewer", async (path, target, kind) => {
+    const resolve = vi.spyOn(commands, "lspResolveClassFile").mockResolvedValue({ status: "ok", data: target });
+    ctrl = new EditorController(createMemoryBackend({ [target]: TEXT }));
+    ctrl.start();
+    try {
+      await ctrl.openFile(path!, { focus: false });
+      expect(resolve).toHaveBeenCalledWith(path);
+      expect(activeTab().input).toMatchObject({ path: target, kind });
+      expect(ctrl.slotFor(activeTab().id)!.model.ctx().readOnly).toBe(kind === "virtual");
+    } finally {
+      resolve.mockRestore();
+    }
+  });
+
   it("opens a URI read-only at the target and keeps it out of the saved session", async () => {
     ctrl = new EditorController(createMemoryBackend({ "/p/App.java": "class App {}\n", [JDT]: TEXT }));
     ctrl.start();

src/features/debugger/__tests__/actions.test.ts

@@ -268,3 +268,23 @@ describe("debugger actions (IDEA parity)", () => {
     expect(useOverlays.getState().evaluate?.expression).toBe("total = order.items\nfor i in x:");
   });
 });
+
+describe("output class breakpoint restrictions", () => {
+  it.each([
+    "debug.toggleBreakpoint",
+    "debug.toggleTemporaryBreakpoint",
+    "debug.toggleMethodBreakpoint",
+    "debug.toggleFieldWatchpoint",
+    "debug.runToCursor",
+    "debug.forceRunToCursor",
+  ])("blocks %s for a source-less output class", async (id) => {
+    paused();
+    const path = "file:///p/target/classes/p/C.class";
+    caret(path, "java", "class C {\n int n;\n void run() {}\n}", 2);
+    await executeAction(id);
+    expect(breakpointsOf(path)).toHaveLength(0);
+    expect(useSpecialBreakpoints.getState().methods).toHaveLength(0);
+    expect(useSpecialBreakpoints.getState().fields).toHaveLength(0);
+    expect(ipc.debugRunTo).not.toHaveBeenCalled();
+  });
+});

src/features/debugger/__tests__/editor.test.ts

@@ -53,6 +53,32 @@ describe("breakpoint gutter", () => {
   });
 });
 
+describe("output class gutter", () => {
+  it("disables ordinary, temporary and logging breakpoints and explains why", () => {
+    loadBreakpoints("/proj");
+    const path = "file:///proj/target/classes/C.class";
+    const view = new EditorView({
+      state: EditorState.create({
+        doc: "class C {}",
+        extensions: [
+          lineNumbers(),
+          breakpointGutter({ ...ctx, path, language: "java", readOnly: true, virtual: true }),
+        ],
+      }),
+      parent: document.body,
+    });
+    views.push(view);
+    const cell = view.dom.querySelector(".cm-lineNumbers .cm-gutterElement")!;
+    cell.dispatchEvent(new MouseEvent("mouseover", { bubbles: true }));
+    expect(cell.closest(".cm-gutters")?.getAttribute("title")).toMatch(/output classes without source code/);
+    for (const modifier of [{}, { altKey: true }, { shiftKey: true }]) {
+      cell.dispatchEvent(new MouseEvent("mousedown", { bubbles: true, button: 0, ...modifier }));
+      cell.dispatchEvent(new MouseEvent("mouseup", { bubbles: true, button: 0, ...modifier }));
+    }
+    expect(breakpointsOf(path)).toHaveLength(0);
+  });
+});
+
 describe("breakpoint look", () => {
   it("shows the verified icon only while a session has bound it", () => {
     const b = { id: "1", line: 0, enabled: true, condition: null, logMessage: null, hitCondition: null };

src/features/debugger/actions.ts

@@ -5,6 +5,7 @@ import { downloadJdkActions } from "@/platform/jdk";
 import { useProject } from "@/platform/project";
 import { activeEditor } from "@/editor/api";
 import { maybeEditorService, notifications, showStatusInfo, toolWindowService } from "@/workbench/contributions";
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import { canPlaceBreakpoint } from "./breakpoints/languages";
 import {
   removeAllBreakpoints,
@@ -75,10 +76,18 @@ function pausedTarget(): { s: DebugSession; thread: number } | null {
   return thread == null ? null : { s, thread };
 }
 
+function breakpointPathAllowed(path: string): boolean {
+  const reason = classFileBreakpointReason(path);
+  if (!reason) return true;
+  showStatusInfo(tx(reason));
+  return false;
+}
+
 /** Run to Cursor at `line` (0-based) of `path` in the paused session. */
 export function runToLine(path: string, line: number) {
   const t = pausedTarget();
-  if (t) void report("Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, path, line, false)));
+  if (t && breakpointPathAllowed(path))
+    void report("Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, path, line, false)));
 }
 
 function notSupported(what: string, s: DebugSession) {
@@ -518,7 +527,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const t = pausedTarget();
         const c = cursor();
-        if (t && c)
+        if (t && c && breakpointPathAllowed(c.path))
           void report("Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, c.path, c.line, false)));
       },
     },
@@ -532,7 +541,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const t = pausedTarget();
         const c = cursor();
-        if (t && c)
+        if (t && c && breakpointPathAllowed(c.path))
           void report("Force Run to Cursor failed", call(commands.debugRunTo(t.s.id, t.thread, c.path, c.line, true)));
       },
     },
@@ -543,7 +552,7 @@ export function registerDebugActions(): () => void {
       icon: "breakpoint",
       run: () => {
         const c = cursor();
-        if (!c) return;
+        if (!c || !breakpointPathAllowed(c.path)) return;
         const exists = useBreakpoints.getState().byFile[c.path]?.some((b) => b.line === c.line);
         const language = activeEditor()?.ctx.language ?? "";
         if (!exists && !canPlaceBreakpoint(language)) {
@@ -568,7 +577,8 @@ export function registerDebugActions(): () => void {
       description: "A line breakpoint that is removed after it is hit",
       run: () => {
         const c = cursor();
-        if (c && canPlaceBreakpoint(activeEditor()?.ctx.language ?? "")) toggleTemporaryBreakpoint(c.path, c.line);
+        if (c && breakpointPathAllowed(c.path) && canPlaceBreakpoint(activeEditor()?.ctx.language ?? "", c.path))
+          toggleTemporaryBreakpoint(c.path, c.line);
       },
     },
     {
@@ -579,7 +589,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const ed = activeEditor();
         const c = cursor();
-        if (!ed || !c) return;
+        if (!ed || !c || !breakpointPathAllowed(c.path)) return;
         const existing = specialAt(c.path).find((b) => b.kind === "method" && b.line === c.line);
         const method = methodAt(ed.ctx.language, ed.view.state.doc.toString(), c.line);
         if (!existing && !method) {
@@ -602,7 +612,7 @@ export function registerDebugActions(): () => void {
       run: () => {
         const ed = activeEditor();
         const c = cursor();
-        if (!ed || !c) return;
+        if (!ed || !c || !breakpointPathAllowed(c.path)) return;
         const existing = specialAt(c.path).find((b) => b.kind === "field" && b.line === c.line);
         const field = fieldAt(ed.ctx.language, ed.view.state.doc.toString(), c.line);
         if (!existing && !field) {

src/features/debugger/breakpoints/languages.ts

@@ -3,6 +3,7 @@
  * when off, new line breakpoints go only into files of languages that have a
  * debug adapter (`languages/*.toml` `[debugger]`).
  */
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import { commands, isTauri } from "@/platform/ipc";
 import { workflowSettings } from "@/platform/workflowSettings";
 
@@ -22,7 +23,8 @@ function load() {
 }
 
 /** Whether a new breakpoint may be placed in a file of `language`. */
-export function canPlaceBreakpoint(language: string): boolean {
+export function canPlaceBreakpoint(language: string, path = ""): boolean {
+  if (classFileBreakpointReason(path)) return false;
   if (workflowSettings().debugger.breakpointsAnyFile) return true;
   load();
   // Until the language list is known, don't block anything.

src/features/debugger/editor/breakpointGutter.ts

@@ -15,6 +15,9 @@ import {
   updateBreakpoint,
   useBreakpoints,
 } from "../breakpoints/store";
+import { classFileBreakpointReason } from "@/platform/classFiles";
+import { tx } from "@/platform/i18n";
+import { showStatusInfo } from "@/workbench/contributions";
 import { canPlaceBreakpoint } from "../breakpoints/languages";
 import {
   removeSpecial,
@@ -129,6 +132,31 @@ function inBreakpointArea(e: MouseEvent): boolean {
 }
 
 export function breakpointGutter(ctx: EditorDocContext): Extension {
+  const reason = classFileBreakpointReason(ctx.path);
+  if (reason) {
+    const message = tx(reason);
+    return ViewPlugin.fromClass(
+      class {
+        constructor(readonly view: EditorView) {
+          view.dom.addEventListener("mouseover", this.hover);
+          view.dom.addEventListener("mousedown", this.down, true);
+        }
+        hover = (e: MouseEvent) => {
+          if (inBreakpointArea(e)) (e.target as HTMLElement).closest(".cm-gutters")?.setAttribute("title", message);
+        };
+        down = (e: MouseEvent) => {
+          if (!inBreakpointArea(e)) return;
+          showStatusInfo(message);
+        };
+        destroy() {
+          this.view.dom.removeEventListener("mouseover", this.hover);
+          this.view.dom.removeEventListener("mousedown", this.down, true);
+          const gutters = this.view.dom.querySelector(".cm-gutters");
+          if (gutters?.getAttribute("title") === message) gutters.removeAttribute("title");
+        }
+      },
+    );
+  }
   const path = ctx.path;
   const field = StateField.define<RangeSet<BreakpointMarker>>({
     create: (state) => buildMarkers(state, path),

src/features/debugger/editor/runToCursor.ts

@@ -3,6 +3,7 @@
  * line shows a small button left of its text that runs to that line (Resume on
  * the execution line itself). Settings › Debugger › "Show inlay Run to Cursor popup".
  */
+import { classFileBreakpointReason } from "@/platform/classFiles";
 import type { Extension } from "@codemirror/state";
 import { EditorView, ViewPlugin } from "@codemirror/view";
 import type { EditorDocContext } from "@/editor/api";
@@ -30,7 +31,7 @@ export function hoveredLine(
 }
 
 export function runToCursorInlay(ctx: EditorDocContext): Extension {
-  if (ctx.virtual) return [];
+  if (classFileBreakpointReason(ctx.path) || (ctx.virtual && !ctx.path.startsWith("jdt:"))) return [];
   const path = ctx.path;
   return ViewPlugin.fromClass(
     class {

src/platform/classFiles.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it, vi } from "vitest";
+import { classFileBreakpointReason, isClassFile } from "./classFiles";
+import { isVirtualUri } from "./virtualDocs";
+import { canPlaceBreakpoint } from "@/features/debugger/breakpoints/languages";
+vi.mock("@/platform/workflowSettings", () => ({
+  workflowSettings: () => ({ debugger: { breakpointsAnyFile: true } }),
+}));
+
+describe("compiled class routing and breakpoint policy", () => {
+  it.each([
+    "/p/target/classes/p/C.class",
+    "/p/build/classes/java/main/p/C$1.class",
+    "C:\\p\\out\\C.class",
+    "file:///p/out/C.class",
+  ])("disables output breakpoints even with any-file enabled: %s", (path) => {
+    expect(isClassFile(path)).toBe(true);
+    expect(classFileBreakpointReason(path)).toBeTruthy();
+    expect(canPlaceBreakpoint("java", path)).toBe(false);
+  });
+  it.each([
+    "jdt://contents/a.jar/p/C.class?=p/a.jar%3Cp%28C.class",
+    "jdt://contents/a.jar/p/C.java?=p/a.jar%3Cp%28C.class",
+    "/p/src/main/java/p/C.java",
+  ])("keeps source and JDT breakpoints enabled: %s", (path) => {
+    expect(isClassFile(path)).toBe(false);
+    expect(classFileBreakpointReason(path)).toBeNull();
+    expect(canPlaceBreakpoint("java", path)).toBe(true);
+  });
+  it("treats disk class URIs as read-only server documents", () => {
+    expect(isVirtualUri("file:///p/out/C.class")).toBe(true);
+    expect(isVirtualUri("file:///p/src/C.java")).toBe(false);
+    expect(isClassFile("/m2/a.jar!/p/C.class")).toBe(true);
+  });
+});

src/platform/classFiles.ts

@@ -0,0 +1,8 @@
+/** Compiled Java files are resolved before the binary viewer, at every opening entry. */
+export function isClassFile(path: string): boolean {
+  return !path.startsWith("jdt:") && /\.class$/i.test(path);
+}
+
+export function classFileBreakpointReason(path: string): string | null {
+  return isClassFile(path) ? "Breakpoints are not supported in output classes without source code." : null;
+}

src/platform/locales/text/zh.json

@@ -4467,6 +4467,7 @@
   "Plan node properties": "计划节点属性",
   "Values": "值",
   "Vim rc file": "Vim rc 文件",
+  "Breakpoints are not supported in output classes without source code.": "输出目录中无源码的类不支持断点。",
   "Decompiled .class file: sources are not available.": "已反编译的 .class 文件：没有可用的源代码。",
   "No column of the file matches the table": "文件中没有与该表匹配的列",
   "Not a URL of PostgreSQL, MySQL, SQLite or a compatible database": "不是 PostgreSQL、MySQL、SQLite 或兼容数据库的 URL",

src/platform/virtualDocs.ts

@@ -4,12 +4,13 @@
  * code). Locations into them carry the URI as their `path`; the editor opens
  * them as `virtual` editor inputs instead of files.
  */
+import { isClassFile } from "./classFiles";
 import { call, commands, type VirtualDocument } from "./ipc";
 
-/** True for `scheme:…` URIs other than `file:` (scheme of 2+ chars, so `C:\…` is a path). */
+/** Server document URIs, including decompiled disk classes; drive letters remain paths. */
 export function isVirtualUri(s: string | null | undefined): boolean {
   const m = /^([a-zA-Z][a-zA-Z0-9+.-]+):/.exec(s ?? "");
-  return !!m && m[1]!.toLowerCase() !== "file";
+  return !!m && (m[1]!.toLowerCase() !== "file" || isClassFile(s!));
 }
 
 /** Last path segment of a URI (without query / fragment), e.g. `SpringApplication.class`. */