diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 0cb75c71b7346..aa3749334d97d 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -145,6 +145,25 @@ impl JsonEmitter {
     pub fn ignored_directories_in_source_blocks(self, value: Vec<String>) -> Self {
         Self { ignored_directories_in_source_blocks: value, ..self }
     }
+
+    fn emit(&mut self, val: EmitTyped<'_>) -> io::Result<()> {
+        if self.pretty {
+            serde_json::to_writer_pretty(&mut *self.dst, &val)?
+        } else {
+            serde_json::to_writer(&mut *self.dst, &val)?
+        };
+        self.dst.write_all(b"\n")?;
+        self.dst.flush()
+    }
+}
+
+#[derive(Serialize)]
+#[serde(tag = "$message_type", rename_all = "snake_case")]
+enum EmitTyped<'a> {
+    Diagnostic(Diagnostic),
+    Artifact(ArtifactNotification<'a>),
+    FutureIncompat(FutureIncompatReport<'a>),
+    UnusedExtern(UnusedExterns<'a, 'a, 'a>),
 }
 
 impl Translate for JsonEmitter {
@@ -160,12 +179,7 @@ impl Translate for JsonEmitter {
 impl Emitter for JsonEmitter {
     fn emit_diagnostic(&mut self, diag: &crate::Diagnostic) {
         let data = Diagnostic::from_errors_diagnostic(diag, self);
-        let result = if self.pretty {
-            writeln!(&mut self.dst, "{}", serde_json::to_string_pretty(&data).unwrap())
-        } else {
-            writeln!(&mut self.dst, "{}", serde_json::to_string(&data).unwrap())
-        }
-        .and_then(|_| self.dst.flush());
+        let result = self.emit(EmitTyped::Diagnostic(data));
         if let Err(e) = result {
             panic!("failed to print diagnostics: {e:?}");
         }
@@ -173,34 +187,28 @@ impl Emitter for JsonEmitter {
 
     fn emit_artifact_notification(&mut self, path: &Path, artifact_type: &str) {
         let data = ArtifactNotification { artifact: path, emit: artifact_type };
-        let result = if self.pretty {
-            writeln!(&mut self.dst, "{}", serde_json::to_string_pretty(&data).unwrap())
-        } else {
-            writeln!(&mut self.dst, "{}", serde_json::to_string(&data).unwrap())
-        }
-        .and_then(|_| self.dst.flush());
+        let result = self.emit(EmitTyped::Artifact(data));
         if let Err(e) = result {
             panic!("failed to print notification: {e:?}");
         }
     }
 
     fn emit_future_breakage_report(&mut self, diags: Vec<crate::Diagnostic>) {
-        let data: Vec<FutureBreakageItem> = diags
+        let data: Vec<FutureBreakageItem<'_>> = diags
             .into_iter()
             .map(|mut diag| {
                 if diag.level == crate::Level::Allow {
                     diag.level = crate::Level::Warning(None);
                 }
-                FutureBreakageItem { diagnostic: Diagnostic::from_errors_diagnostic(&diag, self) }
+                FutureBreakageItem {
+                    diagnostic: EmitTyped::Diagnostic(Diagnostic::from_errors_diagnostic(
+                        &diag, self,
+                    )),
+                }
             })
             .collect();
         let report = FutureIncompatReport { future_incompat_report: data };
-        let result = if self.pretty {
-            writeln!(&mut self.dst, "{}", serde_json::to_string_pretty(&report).unwrap())
-        } else {
-            writeln!(&mut self.dst, "{}", serde_json::to_string(&report).unwrap())
-        }
-        .and_then(|_| self.dst.flush());
+        let result = self.emit(EmitTyped::FutureIncompat(report));
         if let Err(e) = result {
             panic!("failed to print future breakage report: {e:?}");
         }
@@ -209,12 +217,7 @@ impl Emitter for JsonEmitter {
     fn emit_unused_externs(&mut self, lint_level: rustc_lint_defs::Level, unused_externs: &[&str]) {
         let lint_level = lint_level.as_str();
         let data = UnusedExterns { lint_level, unused_extern_names: unused_externs };
-        let result = if self.pretty {
-            writeln!(&mut self.dst, "{}", serde_json::to_string_pretty(&data).unwrap())
-        } else {
-            writeln!(&mut self.dst, "{}", serde_json::to_string(&data).unwrap())
-        }
-        .and_then(|_| self.dst.flush());
+        let result = self.emit(EmitTyped::UnusedExtern(data));
         if let Err(e) = result {
             panic!("failed to print unused externs: {e:?}");
         }
@@ -313,13 +316,15 @@ struct ArtifactNotification<'a> {
 }
 
 #[derive(Serialize)]
-struct FutureBreakageItem {
-    diagnostic: Diagnostic,
+struct FutureBreakageItem<'a> {
+    // Always EmitTyped::Diagnostic, but we want to make sure it gets serialized
+    // with "$message_type".
+    diagnostic: EmitTyped<'a>,
 }
 
 #[derive(Serialize)]
-struct FutureIncompatReport {
-    future_incompat_report: Vec<FutureBreakageItem>,
+struct FutureIncompatReport<'a> {
+    future_incompat_report: Vec<FutureBreakageItem<'a>>,
 }
 
 // NOTE: Keep this in sync with the equivalent structs in rustdoc's
diff --git a/src/doc/rustc/src/json.md b/src/doc/rustc/src/json.md
index 11d7b5b59381b..9daa0810126b7 100644
--- a/src/doc/rustc/src/json.md
+++ b/src/doc/rustc/src/json.md
@@ -11,9 +11,11 @@ If parsing the output with Rust, the
 [`cargo_metadata`](https://crates.io/crates/cargo_metadata) crate provides
 some support for parsing the messages.
 
-When parsing, care should be taken to be forwards-compatible with future changes
-to the format. Optional values may be `null`. New fields may be added. Enumerated
-fields like "level" or "suggestion_applicability" may add new values.
+Each type of message has a `$message_type` field which can be used to
+distinguish the different formats. When parsing, care should be taken
+to be forwards-compatible with future changes to the format. Optional
+values may be `null`. New fields may be added. Enumerated fields like
+"level" or "suggestion_applicability" may add new values.
 
 ## Diagnostics
 
@@ -29,6 +31,8 @@ Diagnostics have the following format:
 
 ```javascript
 {
+    /* Type of this message */
+    "$message_type": "diagnostic",
     /* The primary message. */
     "message": "unused variable: `x`",
     /* The diagnostic code.
@@ -217,6 +221,8 @@ flag][option-emit] documentation.
 
 ```javascript
 {
+    /* Type of this message */
+    "$message_type": "artifact",
     /* The filename that was generated. */
     "artifact": "libfoo.rlib",
     /* The kind of artifact that was generated. Possible values:
@@ -239,6 +245,8 @@ information, even if the diagnostics have been suppressed (such as with an
 
 ```javascript
 {
+    /* Type of this message */
+    "$message_type": "future_incompat",
     /* An array of objects describing a warning that will become a hard error
        in the future.
     */
diff --git a/tests/ui/diagnostic-width/flag-json.stderr b/tests/ui/diagnostic-width/flag-json.stderr
index b21391d1640ef..16c17526809d6 100644
--- a/tests/ui/diagnostic-width/flag-json.stderr
+++ b/tests/ui/diagnostic-width/flag-json.stderr
@@ -1,4 +1,4 @@
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -33,8 +33,8 @@ LL | ..._: () = 42;
    |       expected due to this
 
 "}
-{"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
+{"$message_type":"diagnostic","message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
 
 "}
-{"message":"For more information about this error, try `rustc --explain E0308`.","code":null,"level":"failure-note","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0308`.
+{"$message_type":"diagnostic","message":"For more information about this error, try `rustc --explain E0308`.","code":null,"level":"failure-note","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0308`.
 "}
diff --git a/tests/ui/json/json-bom-plus-crlf-multifile.stderr b/tests/ui/json/json-bom-plus-crlf-multifile.stderr
index 84040e8050e96..0c6c654d60a15 100644
--- a/tests/ui/json/json-bom-plus-crlf-multifile.stderr
+++ b/tests/ui/json/json-bom-plus-crlf-multifile.stderr
@@ -1,4 +1,4 @@
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -26,7 +26,7 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":621,"byte_end":622,"line_start":17,"line_end":17,"column_start":22,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1;  // Error in the middle of line.","highlight_start":22,"highlight_end":23}],"label":"expected `String`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":612,"byte_end":618,"line_start":17,"line_end":17,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String = 1;  // Error in the middle of line.","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"try using a conversion method","code":null,"level":"help","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":622,"byte_end":622,"line_start":17,"line_end":17,"column_start":23,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1;  // Error in the middle of line.","highlight_start":23,"highlight_end":23}],"label":null,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","expansion":null}],"children":[],"rendered":null}],"rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:17:22: error[E0308]: mismatched types
 "}
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -54,7 +54,7 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":681,"byte_end":682,"line_start":19,"line_end":19,"column_start":22,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1","highlight_start":22,"highlight_end":23}],"label":"expected `String`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":672,"byte_end":678,"line_start":19,"line_end":19,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String = 1","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"try using a conversion method","code":null,"level":"help","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":682,"byte_end":682,"line_start":19,"line_end":19,"column_start":23,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1","highlight_start":23,"highlight_end":23}],"label":null,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","expansion":null}],"children":[],"rendered":null}],"rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:19:22: error[E0308]: mismatched types
 "}
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -82,7 +82,7 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":745,"byte_end":746,"line_start":23,"line_end":23,"column_start":1,"column_end":2,"is_primary":true,"text":[{"text":"1;  // Error after the newline.","highlight_start":1,"highlight_end":2}],"label":"expected `String`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":735,"byte_end":741,"line_start":22,"line_end":22,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String =","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"try using a conversion method","code":null,"level":"help","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":746,"byte_end":746,"line_start":23,"line_end":23,"column_start":2,"column_end":2,"is_primary":true,"text":[{"text":"1;  // Error after the newline.","highlight_start":2,"highlight_end":2}],"label":null,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","expansion":null}],"children":[],"rendered":null}],"rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:23:1: error[E0308]: mismatched types
 "}
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -110,5 +110,5 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":801,"byte_end":809,"line_start":25,"line_end":26,"column_start":22,"column_end":6,"is_primary":true,"text":[{"text":"    let s : String = (","highlight_start":22,"highlight_end":23},{"text":"    );  // Error spanning the newline.","highlight_start":1,"highlight_end":6}],"label":"expected `String`, found `()`","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","byte_start":792,"byte_end":798,"line_start":25,"line_end":25,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String = (","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:25:22: error[E0308]: mismatched types
 "}
-{"message":"aborting due to 4 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 4 previous errors
+{"$message_type":"diagnostic","message":"aborting due to 4 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 4 previous errors
 "}
diff --git a/tests/ui/json/json-bom-plus-crlf.stderr b/tests/ui/json/json-bom-plus-crlf.stderr
index b0f450e9ecc14..31dbacb59e1ee 100644
--- a/tests/ui/json/json-bom-plus-crlf.stderr
+++ b/tests/ui/json/json-bom-plus-crlf.stderr
@@ -1,4 +1,4 @@
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -26,7 +26,7 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":606,"byte_end":607,"line_start":16,"line_end":16,"column_start":22,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1;  // Error in the middle of line.","highlight_start":22,"highlight_end":23}],"label":"expected `String`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":597,"byte_end":603,"line_start":16,"line_end":16,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String = 1;  // Error in the middle of line.","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"try using a conversion method","code":null,"level":"help","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":607,"byte_end":607,"line_start":16,"line_end":16,"column_start":23,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1;  // Error in the middle of line.","highlight_start":23,"highlight_end":23}],"label":null,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","expansion":null}],"children":[],"rendered":null}],"rendered":"$DIR/json-bom-plus-crlf.rs:16:22: error[E0308]: mismatched types
 "}
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -54,7 +54,7 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":666,"byte_end":667,"line_start":18,"line_end":18,"column_start":22,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1","highlight_start":22,"highlight_end":23}],"label":"expected `String`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":657,"byte_end":663,"line_start":18,"line_end":18,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String = 1","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"try using a conversion method","code":null,"level":"help","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":667,"byte_end":667,"line_start":18,"line_end":18,"column_start":23,"column_end":23,"is_primary":true,"text":[{"text":"    let s : String = 1","highlight_start":23,"highlight_end":23}],"label":null,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","expansion":null}],"children":[],"rendered":null}],"rendered":"$DIR/json-bom-plus-crlf.rs:18:22: error[E0308]: mismatched types
 "}
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -82,7 +82,7 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":730,"byte_end":731,"line_start":22,"line_end":22,"column_start":1,"column_end":2,"is_primary":true,"text":[{"text":"1;  // Error after the newline.","highlight_start":1,"highlight_end":2}],"label":"expected `String`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":720,"byte_end":726,"line_start":21,"line_end":21,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String =","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"try using a conversion method","code":null,"level":"help","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":731,"byte_end":731,"line_start":22,"line_end":22,"column_start":2,"column_end":2,"is_primary":true,"text":[{"text":"1;  // Error after the newline.","highlight_start":2,"highlight_end":2}],"label":null,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","expansion":null}],"children":[],"rendered":null}],"rendered":"$DIR/json-bom-plus-crlf.rs:22:1: error[E0308]: mismatched types
 "}
-{"message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
+{"$message_type":"diagnostic","message":"mismatched types","code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -110,5 +110,5 @@ most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
 "},"level":"error","spans":[{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":786,"byte_end":794,"line_start":24,"line_end":25,"column_start":22,"column_end":6,"is_primary":true,"text":[{"text":"    let s : String = (","highlight_start":22,"highlight_end":23},{"text":"    );  // Error spanning the newline.","highlight_start":1,"highlight_end":6}],"label":"expected `String`, found `()`","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/json-bom-plus-crlf.rs","byte_start":777,"byte_end":783,"line_start":24,"line_end":24,"column_start":13,"column_end":19,"is_primary":false,"text":[{"text":"    let s : String = (","highlight_start":13,"highlight_end":19}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"$DIR/json-bom-plus-crlf.rs:24:22: error[E0308]: mismatched types
 "}
-{"message":"aborting due to 4 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 4 previous errors
+{"$message_type":"diagnostic","message":"aborting due to 4 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 4 previous errors
 "}
diff --git a/tests/ui/json/json-multiple.stderr b/tests/ui/json/json-multiple.stderr
index 55ccfd5fa70de..7689fb94a6c8d 100644
--- a/tests/ui/json/json-multiple.stderr
+++ b/tests/ui/json/json-multiple.stderr
@@ -1 +1 @@
-{"artifact":"$TEST_BUILD_DIR/json/json-multiple/libjson_multiple.rlib","emit":"link"}
+{"$message_type":"artifact","artifact":"$TEST_BUILD_DIR/json/json-multiple/libjson_multiple.rlib","emit":"link"}
diff --git a/tests/ui/json/json-options.stderr b/tests/ui/json/json-options.stderr
index 645a26f5ad407..668fc18097f0d 100644
--- a/tests/ui/json/json-options.stderr
+++ b/tests/ui/json/json-options.stderr
@@ -1 +1 @@
-{"artifact":"$TEST_BUILD_DIR/json/json-options/libjson_options.rlib","emit":"link"}
+{"$message_type":"artifact","artifact":"$TEST_BUILD_DIR/json/json-options/libjson_options.rlib","emit":"link"}
diff --git a/tests/ui/json/json-short.stderr b/tests/ui/json/json-short.stderr
index 3bd85b083d002..030af0c5ada61 100644
--- a/tests/ui/json/json-short.stderr
+++ b/tests/ui/json/json-short.stderr
@@ -1,4 +1,4 @@
-{"message":"`main` function not found in crate `json_short`","code":{"code":"E0601","explanation":"No `main` function was found in a binary crate.
+{"$message_type":"diagnostic","message":"`main` function not found in crate `json_short`","code":{"code":"E0601","explanation":"No `main` function was found in a binary crate.
 
 To fix this error, add a `main` function:
 
@@ -15,5 +15,5 @@ If you don't know the basics of Rust, you can look at the
 [rust-book]: https://doc.rust-lang.org/book/
 "},"level":"error","spans":[{"file_name":"$DIR/json-short.rs","byte_start":62,"byte_end":62,"line_start":1,"line_end":1,"column_start":63,"column_end":63,"is_primary":true,"text":[{"text":"// compile-flags: --json=diagnostic-short --error-format=json","highlight_start":63,"highlight_end":63}],"label":"consider adding a `main` function to `$DIR/json-short.rs`","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"$DIR/json-short.rs:1:63: error[E0601]: `main` function not found in crate `json_short`
 "}
-{"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
+{"$message_type":"diagnostic","message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
 "}
diff --git a/tests/ui/lint/future-incompat-json-test.rs b/tests/ui/lint/future-incompat-json-test.rs
new file mode 100644
index 0000000000000..6ccd670294c60
--- /dev/null
+++ b/tests/ui/lint/future-incompat-json-test.rs
@@ -0,0 +1,10 @@
+// compile-flags: -Zfuture-incompat-test --json=future-incompat --error-format=json
+// check-pass
+
+// The `-Zfuture-incompat-test flag causes any normal warning to be included
+// in the future-incompatible report. The stderr output here should mention
+// the future incompatible report (as extracted by compiletest).
+
+fn main() {
+    let x = 1;
+}
diff --git a/tests/ui/lint/future-incompat-json-test.stderr b/tests/ui/lint/future-incompat-json-test.stderr
new file mode 100644
index 0000000000000..c4ab5a00d16cc
--- /dev/null
+++ b/tests/ui/lint/future-incompat-json-test.stderr
@@ -0,0 +1,10 @@
+{"$message_type":"future_incompat","future_incompat_report":[{"diagnostic":{"$message_type":"diagnostic","message":"unused variable: `x`","code":{"code":"unused_variables","explanation":null},"level":"warning","spans":[{"file_name":"$DIR/future-incompat-json-test.rs","byte_start":338,"byte_end":339,"line_start":9,"line_end":9,"column_start":9,"column_end":10,"is_primary":true,"text":[{"text":"    let x = 1;","highlight_start":9,"highlight_end":10}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"`-A unused-variables` implied by `-A unused`","code":null,"level":"note","spans":[],"children":[],"rendered":null},{"message":"to override `-A unused` add `#[allow(unused_variables)]`","code":null,"level":"help","spans":[],"children":[],"rendered":null},{"message":"if this is intentional, prefix it with an underscore","code":null,"level":"help","spans":[{"file_name":"$DIR/future-incompat-json-test.rs","byte_start":338,"byte_end":339,"line_start":9,"line_end":9,"column_start":9,"column_end":10,"is_primary":true,"text":[{"text":"    let x = 1;","highlight_start":9,"highlight_end":10}],"label":null,"suggested_replacement":"_x","suggestion_applicability":"MachineApplicable","expansion":null}],"children":[],"rendered":null}],"rendered":"warning: unused variable: `x`
+  --> $DIR/future-incompat-json-test.rs:9:9
+   |
+LL |     let x = 1;
+   |         ^ help: if this is intentional, prefix it with an underscore: `_x`
+   |
+   = note: `-A unused-variables` implied by `-A unused`
+   = help: to override `-A unused` add `#[allow(unused_variables)]`
+
+"}}]}
diff --git a/tests/ui/lint/unused_parens_json_suggestion.stderr b/tests/ui/lint/unused_parens_json_suggestion.stderr
index ea19e0cdc0cb3..ac3b2b5b21a71 100644
--- a/tests/ui/lint/unused_parens_json_suggestion.stderr
+++ b/tests/ui/lint/unused_parens_json_suggestion.stderr
@@ -1,4 +1,4 @@
-{"message":"unnecessary parentheses around assigned value","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_json_suggestion.rs","byte_start":577,"byte_end":578,"line_start":16,"line_end":16,"column_start":14,"column_end":15,"is_primary":true,"text":[{"text":"    let _a = (1 / (2 + 3));
+{"$message_type":"diagnostic","message":"unnecessary parentheses around assigned value","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_json_suggestion.rs","byte_start":577,"byte_end":578,"line_start":16,"line_end":16,"column_start":14,"column_end":15,"is_primary":true,"text":[{"text":"    let _a = (1 / (2 + 3));
   --> $DIR/unused_parens_json_suggestion.rs:16:14
    |
 LL |     let _a = (1 / (2 + 3));
@@ -16,6 +16,6 @@ LL +     let _a = 1 / (2 + 3);
    |
 
 "}
-{"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
+{"$message_type":"diagnostic","message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
 
 "}
diff --git a/tests/ui/lint/unused_parens_remove_json_suggestion.stderr b/tests/ui/lint/unused_parens_remove_json_suggestion.stderr
index f4c6ceaf1dc1b..7521d41cc939d 100644
--- a/tests/ui/lint/unused_parens_remove_json_suggestion.stderr
+++ b/tests/ui/lint/unused_parens_remove_json_suggestion.stderr
@@ -1,4 +1,4 @@
-{"message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":481,"byte_end":482,"line_start":17,"line_end":17,"column_start":8,"column_end":9,"is_primary":true,"text":[{"text":"    if (_b) {
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":481,"byte_end":482,"line_start":17,"line_end":17,"column_start":8,"column_end":9,"is_primary":true,"text":[{"text":"    if (_b) {
   --> $DIR/unused_parens_remove_json_suggestion.rs:17:8
    |
 LL |     if (_b) {
@@ -16,7 +16,7 @@ LL +     if _b {
    |
 
 "}
-{"message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":612,"byte_end":613,"line_start":28,"line_end":28,"column_start":7,"column_end":8,"is_primary":true,"text":[{"text":"    if(c) {
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":612,"byte_end":613,"line_start":28,"line_end":28,"column_start":7,"column_end":8,"is_primary":true,"text":[{"text":"    if(c) {
   --> $DIR/unused_parens_remove_json_suggestion.rs:28:7
    |
 LL |     if(c) {
@@ -29,7 +29,7 @@ LL +     if c {
    |
 
 "}
-{"message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":692,"byte_end":693,"line_start":32,"line_end":32,"column_start":8,"column_end":9,"is_primary":true,"text":[{"text":"    if (c){
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":692,"byte_end":693,"line_start":32,"line_end":32,"column_start":8,"column_end":9,"is_primary":true,"text":[{"text":"    if (c){
   --> $DIR/unused_parens_remove_json_suggestion.rs:32:8
    |
 LL |     if (c){
@@ -42,7 +42,7 @@ LL +     if c {
    |
 
 "}
-{"message":"unnecessary parentheses around `while` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":774,"byte_end":775,"line_start":36,"line_end":36,"column_start":11,"column_end":12,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":11,"highlight_end":12}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":788,"byte_end":789,"line_start":36,"line_end":36,"column_start":25,"column_end":26,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":25,"highlight_end":26}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"remove these parentheses","code":null,"level":"help","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":774,"byte_end":775,"line_start":36,"line_end":36,"column_start":11,"column_end":12,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":11,"highlight_end":12}],"label":null,"suggested_replacement":"","suggestion_applicability":"MachineApplicable","expansion":null},{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":788,"byte_end":789,"line_start":36,"line_end":36,"column_start":25,"column_end":26,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":25,"highlight_end":26}],"label":null,"suggested_replacement":" ","suggestion_applicability":"MachineApplicable","expansion":null}],"children":[],"rendered":null}],"rendered":"error: unnecessary parentheses around `while` condition
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `while` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":774,"byte_end":775,"line_start":36,"line_end":36,"column_start":11,"column_end":12,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":11,"highlight_end":12}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":788,"byte_end":789,"line_start":36,"line_end":36,"column_start":25,"column_end":26,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":25,"highlight_end":26}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"remove these parentheses","code":null,"level":"help","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":774,"byte_end":775,"line_start":36,"line_end":36,"column_start":11,"column_end":12,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":11,"highlight_end":12}],"label":null,"suggested_replacement":"","suggestion_applicability":"MachineApplicable","expansion":null},{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":788,"byte_end":789,"line_start":36,"line_end":36,"column_start":25,"column_end":26,"is_primary":true,"text":[{"text":"    while (false && true){","highlight_start":25,"highlight_end":26}],"label":null,"suggested_replacement":" ","suggestion_applicability":"MachineApplicable","expansion":null}],"children":[],"rendered":null}],"rendered":"error: unnecessary parentheses around `while` condition
   --> $DIR/unused_parens_remove_json_suggestion.rs:36:11
    |
 LL |     while (false && true){
@@ -55,7 +55,7 @@ LL +     while false && true {
    |
 
 "}
-{"message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":802,"byte_end":803,"line_start":37,"line_end":37,"column_start":12,"column_end":13,"is_primary":true,"text":[{"text":"        if (c) {
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `if` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":802,"byte_end":803,"line_start":37,"line_end":37,"column_start":12,"column_end":13,"is_primary":true,"text":[{"text":"        if (c) {
   --> $DIR/unused_parens_remove_json_suggestion.rs:37:12
    |
 LL |         if (c) {
@@ -68,7 +68,7 @@ LL +         if c {
    |
 
 "}
-{"message":"unnecessary parentheses around `while` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":899,"byte_end":900,"line_start":43,"line_end":43,"column_start":10,"column_end":11,"is_primary":true,"text":[{"text":"    while(true && false) {
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `while` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":899,"byte_end":900,"line_start":43,"line_end":43,"column_start":10,"column_end":11,"is_primary":true,"text":[{"text":"    while(true && false) {
   --> $DIR/unused_parens_remove_json_suggestion.rs:43:10
    |
 LL |     while(true && false) {
@@ -81,7 +81,7 @@ LL +     while true && false {
    |
 
 "}
-{"message":"unnecessary parentheses around `for` iterator expression","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":968,"byte_end":969,"line_start":44,"line_end":44,"column_start":18,"column_end":19,"is_primary":true,"text":[{"text":"        for _ in (0 .. 3){
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `for` iterator expression","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":968,"byte_end":969,"line_start":44,"line_end":44,"column_start":18,"column_end":19,"is_primary":true,"text":[{"text":"        for _ in (0 .. 3){
   --> $DIR/unused_parens_remove_json_suggestion.rs:44:18
    |
 LL |         for _ in (0 .. 3){
@@ -94,7 +94,7 @@ LL +         for _ in 0 .. 3 {
    |
 
 "}
-{"message":"unnecessary parentheses around `for` iterator expression","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":1069,"byte_end":1070,"line_start":49,"line_end":49,"column_start":14,"column_end":15,"is_primary":true,"text":[{"text":"    for _ in (0 .. 3) {
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `for` iterator expression","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":1069,"byte_end":1070,"line_start":49,"line_end":49,"column_start":14,"column_end":15,"is_primary":true,"text":[{"text":"    for _ in (0 .. 3) {
   --> $DIR/unused_parens_remove_json_suggestion.rs:49:14
    |
 LL |     for _ in (0 .. 3) {
@@ -107,7 +107,7 @@ LL +     for _ in 0 .. 3 {
    |
 
 "}
-{"message":"unnecessary parentheses around `while` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":1128,"byte_end":1129,"line_start":50,"line_end":50,"column_start":15,"column_end":16,"is_primary":true,"text":[{"text":"        while (true && false) {
+{"$message_type":"diagnostic","message":"unnecessary parentheses around `while` condition","code":{"code":"unused_parens","explanation":null},"level":"error","spans":[{"file_name":"$DIR/unused_parens_remove_json_suggestion.rs","byte_start":1128,"byte_end":1129,"line_start":50,"line_end":50,"column_start":15,"column_end":16,"is_primary":true,"text":[{"text":"        while (true && false) {
   --> $DIR/unused_parens_remove_json_suggestion.rs:50:15
    |
 LL |         while (true && false) {
@@ -120,6 +120,6 @@ LL +         while true && false {
    |
 
 "}
-{"message":"aborting due to 9 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 9 previous errors
+{"$message_type":"diagnostic","message":"aborting due to 9 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 9 previous errors
 
 "}
diff --git a/tests/ui/lint/use_suggestion_json.stderr b/tests/ui/lint/use_suggestion_json.stderr
index d17514303abf6..7dfd269a4e247 100644
--- a/tests/ui/lint/use_suggestion_json.stderr
+++ b/tests/ui/lint/use_suggestion_json.stderr
@@ -1,3 +1,3 @@
-{"message":"`--error-format=pretty-json` is unstable","code":null,"level":"error","spans":[],"children":[],"rendered":"\u001b[0m\u001b[1m\u001b[38;5;9merror\u001b[0m\u001b[0m\u001b[1m: `--error-format=pretty-json` is unstable\u001b[0m
+{"$message_type":"diagnostic","message":"`--error-format=pretty-json` is unstable","code":null,"level":"error","spans":[],"children":[],"rendered":"\u001b[0m\u001b[1m\u001b[38;5;9merror\u001b[0m\u001b[0m\u001b[1m: `--error-format=pretty-json` is unstable\u001b[0m
 
 "}
diff --git a/tests/ui/rmeta/emit-artifact-notifications.stderr b/tests/ui/rmeta/emit-artifact-notifications.stderr
index b2f0aa7575c06..4f68a2d74ed31 100644
--- a/tests/ui/rmeta/emit-artifact-notifications.stderr
+++ b/tests/ui/rmeta/emit-artifact-notifications.stderr
@@ -1 +1 @@
-{"artifact":"$TEST_BUILD_DIR/rmeta/emit-artifact-notifications/libemit_artifact_notifications.rmeta","emit":"metadata"}
+{"$message_type":"artifact","artifact":"$TEST_BUILD_DIR/rmeta/emit-artifact-notifications/libemit_artifact_notifications.rmeta","emit":"metadata"}
diff --git a/tests/ui/unused-crate-deps/deny-cmdline-json-silent.stderr b/tests/ui/unused-crate-deps/deny-cmdline-json-silent.stderr
index 595619f3a8a4e..f6594fdaa911e 100644
--- a/tests/ui/unused-crate-deps/deny-cmdline-json-silent.stderr
+++ b/tests/ui/unused-crate-deps/deny-cmdline-json-silent.stderr
@@ -1 +1 @@
-{"lint_level":"deny","unused_extern_names":["bar"]}
+{"$message_type":"unused_extern","lint_level":"deny","unused_extern_names":["bar"]}
diff --git a/tests/ui/unused-crate-deps/deny-cmdline-json.stderr b/tests/ui/unused-crate-deps/deny-cmdline-json.stderr
index 595619f3a8a4e..f6594fdaa911e 100644
--- a/tests/ui/unused-crate-deps/deny-cmdline-json.stderr
+++ b/tests/ui/unused-crate-deps/deny-cmdline-json.stderr
@@ -1 +1 @@
-{"lint_level":"deny","unused_extern_names":["bar"]}
+{"$message_type":"unused_extern","lint_level":"deny","unused_extern_names":["bar"]}
diff --git a/tests/ui/unused-crate-deps/warn-cmdline-json.stderr b/tests/ui/unused-crate-deps/warn-cmdline-json.stderr
index 98dbd763927e6..ef99f986eb1d7 100644
--- a/tests/ui/unused-crate-deps/warn-cmdline-json.stderr
+++ b/tests/ui/unused-crate-deps/warn-cmdline-json.stderr
@@ -1 +1 @@
-{"lint_level":"warn","unused_extern_names":["bar"]}
+{"$message_type":"unused_extern","lint_level":"warn","unused_extern_names":["bar"]}