doc: don't use mergeable info and json together

src/compiler/build_runner/compilation_files.rs

@@ -555,7 +555,7 @@ impl<'a, 'gctx: 'a> CompilationFiles<'a, 'gctx> {
                     flavor: FileFlavor::Normal,
                 }];
 
-                if bcx.gctx.cli_unstable().rustdoc_mergeable_info {
+                if bcx.gctx.cli_unstable().rustdoc_mergeable_info && !wants_json_doc {
                     // `-Zrustdoc-mergeable-info` always uses the new layout.
                     outputs.push(OutputFile {
                         path: self

src/compiler/mod.rs

@@ -871,6 +871,7 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
     let bcx = build_runner.bcx;
     // script_metadata is not needed here, it is only for tests.
     let mut rustdoc = build_runner.compilation.rustdoc_process(unit, None)?;
+    let wants_json_output = build_runner.bcx.build_config.intent.wants_doc_json_output();
     if unit.pkg.manifest().is_embedded() {
         if !bcx.gctx.cli_unstable().script {
             anyhow::bail!(
@@ -889,7 +890,7 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
 
     unit.kind.add_target_arg(&mut rustdoc);
 
-    let doc_dir = if build_runner.bcx.build_config.intent.wants_doc_json_output() {
+    let doc_dir = if wants_json_output {
         // Always use new layout for '--output-format=json'.
         // In fix for https://github.com/rust-lang/cargo/issues/16291
 
@@ -908,7 +909,9 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
     if build_runner.bcx.gctx.cli_unstable().rustdoc_depinfo {
         // html-static-files is required for keeping the shared styling resources
         // html-non-static-files is required for keeping the original rustdoc emission
-        let mut arg = if build_runner.bcx.gctx.cli_unstable().rustdoc_mergeable_info {
+        let mut arg = if wants_json_output {
+            OsString::from("--emit=dep-info=")
+        } else if build_runner.bcx.gctx.cli_unstable().rustdoc_mergeable_info {
             // toolchain resources are written at the end, at the same time as merging
             OsString::from("--emit=html-non-static-files,dep-info=")
         } else {
@@ -921,12 +924,12 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
         if build_runner.bcx.gctx.cli_unstable().checksum_freshness {
             rustdoc.arg("-Z").arg("checksum-hash-algorithm=blake3");
         }
-    } else if build_runner.bcx.gctx.cli_unstable().rustdoc_mergeable_info {
+    } else if build_runner.bcx.gctx.cli_unstable().rustdoc_mergeable_info && !wants_json_output {
         // toolchain resources are written at the end, at the same time as merging
         rustdoc.arg("--emit=html-non-static-files");
     }
 
-    if build_runner.bcx.gctx.cli_unstable().rustdoc_mergeable_info {
+    if build_runner.bcx.gctx.cli_unstable().rustdoc_mergeable_info && !wants_json_output {
         // write out mergeable data to be imported
         rustdoc.arg("-Zunstable-options");
         let mut arg = OsString::from("--write-doc-meta-dir=");

src/ops/cargo_doc.rs

@@ -58,7 +58,8 @@ pub struct DocOptions {
 pub fn doc(ws: &Workspace<'_>, options: &DocOptions) -> CargoResult<()> {
     let compilation = ops::compile(ws, &options.compile_opts)?;
 
-    if ws.gctx().cli_unstable().rustdoc_mergeable_info {
+    let wants_json_doc = matches!(options.output_format, OutputFormat::Json);
+    if ws.gctx().cli_unstable().rustdoc_mergeable_info && !wants_json_doc {
         merge_cross_crate_info(ws, &compilation)?;
     }
 

tests/testsuite/doc.rs

@@ -4214,3 +4214,68 @@ fn doc_output_format_json_with_deps() {
     assert!(!p.root().join("target/doc/foo/index.html").exists());
     assert!(!p.root().join("target/doc/bar/index.html").exists());
 }
+
+#[cargo_test(
+    nightly,
+    reason = "--output-format and -Zrustdoc-mergeable-info are unstable"
+)]
+fn doc_output_format_json_with_deps_and_mergeable_info() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+                edition = "2021"
+
+                [dependencies]
+                bar = { path = "bar" }
+            "#,
+        )
+        .file("src/lib.rs", "pub fn foo_fn() {}")
+        .file(
+            "bar/Cargo.toml",
+            r#"
+                [package]
+                name = "bar"
+                version = "0.1.0"
+                edition = "2021"
+            "#,
+        )
+        .file("bar/src/lib.rs", "pub fn bar_fn() {}")
+        .build();
+
+    p.cargo("doc -Z unstable-options --output-format json -Zrustdoc-mergeable-info -v")
+        .masquerade_as_nightly_cargo(&["rustdoc-output-format"])
+        .with_stderr_data(
+            str![[r#"
+[LOCKING] 1 package to highest compatible version
+[CHECKING] bar v0.1.0 ([ROOT]/foo/bar)
+[RUNNING] `rustc [..]--crate-name bar [..]`
+[DOCUMENTING] bar v0.1.0 ([ROOT]/foo/bar)
+[RUNNING] `rustdoc [..]--crate-name bar [..]--output-format=json[..]`
+[DOCUMENTING] foo v0.1.0 ([ROOT]/foo)
+[RUNNING] `rustdoc [..]--crate-name foo [..]--output-format=json[..]`
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+[GENERATED] [ROOT]/foo/target/doc/foo.json
+
+"#]]
+            .unordered(),
+        )
+        .run();
+
+    let foo_json_path = p.root().join("target/doc/foo.json");
+    let bar_json_path = p.root().join("target/doc/bar.json");
+    assert!(foo_json_path.is_file());
+    assert!(bar_json_path.is_file());
+
+    let foo_json = fs::read_to_string(&foo_json_path).unwrap();
+    assert!(foo_json.contains("foo_fn"));
+
+    let bar_json = fs::read_to_string(&bar_json_path).unwrap();
+    assert!(bar_json.contains("bar_fn"));
+
+    assert!(!p.root().join("target/doc/foo/index.html").exists());
+    assert!(!p.root().join("target/doc/bar/index.html").exists());
+}