Don't emit "executable" JSON field for non-executables.

src/cargo/core/compiler/build_config.rs

@@ -219,4 +219,15 @@ impl CompileMode {
     pub fn is_run_custom_build(self) -> bool {
         self == CompileMode::RunCustomBuild
     }
+
+    /// Returns `true` if this mode may generate an executable.
+    ///
+    /// Note that this also returns `true` for building libraries, so you also
+    /// have to check the target.
+    pub fn generates_executable(self) -> bool {
+        matches!(
+            self,
+            CompileMode::Test | CompileMode::Bench | CompileMode::Build
+        )
+    }
 }

src/cargo/core/compiler/context/mod.rs

@@ -294,19 +294,16 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
 
     /// Returns the executable for the specified unit (if any).
     pub fn get_executable(&mut self, unit: &Unit) -> CargoResult<Option<PathBuf>> {
-        for output in self.outputs(unit)?.iter() {
-            if output.flavor != FileFlavor::Normal {
-                continue;
-            }
-
-            let is_binary = unit.target.is_executable();
-            let is_test = unit.mode.is_any_test() && !unit.mode.is_check();
-
-            if is_binary || is_test {
-                return Ok(Option::Some(output.bin_dst().clone()));
-            }
+        let is_binary = unit.target.is_executable();
+        let is_test = unit.mode.is_any_test();
+        if !unit.mode.generates_executable() || !(is_binary || is_test) {
+            return Ok(None);
         }
-        Ok(None)
+        Ok(self
+            .outputs(unit)?
+            .iter()
+            .find(|o| o.flavor == FileFlavor::Normal)
+            .map(|output| output.bin_dst().clone()))
     }
 
     pub fn prepare_units(&mut self) -> CargoResult<()> {

tests/testsuite/doc.rs

@@ -1638,6 +1638,89 @@ fn doc_message_format() {
         .run();
 }
 
+#[cargo_test]
+fn doc_json_artifacts() {
+    // Checks the output of json artifact messages.
+    let p = project()
+        .file("src/lib.rs", "")
+        .file("src/bin/somebin.rs", "fn main() {}")
+        .build();
+
+    p.cargo("doc --message-format=json")
+        .with_json_contains_unordered(
+            r#"
+{
+    "reason": "compiler-artifact",
+    "package_id": "foo 0.0.1 [..]",
+    "manifest_path": "[ROOT]/foo/Cargo.toml",
+    "target":
+    {
+        "kind": ["lib"],
+        "crate_types": ["lib"],
+        "name": "foo",
+        "src_path": "[ROOT]/foo/src/lib.rs",
+        "edition": "2015",
+        "doc": true,
+        "doctest": true,
+        "test": true
+    },
+    "profile": "{...}",
+    "features": [],
+    "filenames": ["[ROOT]/foo/target/debug/deps/libfoo-[..].rmeta"],
+    "executable": null,
+    "fresh": false
+}
+
+{
+    "reason": "compiler-artifact",
+    "package_id": "foo 0.0.1 [..]",
+    "manifest_path": "[ROOT]/foo/Cargo.toml",
+    "target":
+    {
+        "kind": ["lib"],
+        "crate_types": ["lib"],
+        "name": "foo",
+        "src_path": "[ROOT]/foo/src/lib.rs",
+        "edition": "2015",
+        "doc": true,
+        "doctest": true,
+        "test": true
+    },
+    "profile": "{...}",
+    "features": [],
+    "filenames": ["[ROOT]/foo/target/doc/foo/index.html"],
+    "executable": null,
+    "fresh": false
+}
+
+{
+    "reason": "compiler-artifact",
+    "package_id": "foo 0.0.1 [..]",
+    "manifest_path": "[ROOT]/foo/Cargo.toml",
+    "target":
+    {
+        "kind": ["bin"],
+        "crate_types": ["bin"],
+        "name": "somebin",
+        "src_path": "[ROOT]/foo/src/bin/somebin.rs",
+        "edition": "2015",
+        "doc": true,
+        "doctest": false,
+        "test": true
+    },
+    "profile": "{...}",
+    "features": [],
+    "filenames": ["[ROOT]/foo/target/doc/somebin/index.html"],
+    "executable": null,
+    "fresh": false
+}
+
+{"reason":"build-finished","success":true}
+"#,
+        )
+        .run();
+}
+
 #[cargo_test]
 fn short_message_format() {
     let p = project().file("src/lib.rs", BAD_INTRA_LINK_LIB).build();