Add type field to json diagnostic outputs

Currently the json-formatted outputs have no way to unambiguously
determine which kind of message is being output. A consumer can look for
specific fields in the json object (eg "message"), but there's no
guarantee that in future some other kind of output will have a field of
the same name.

This PR adds a `"type"` field to add json outputs which can be used to
unambiguously determine which kind of output it is. The mapping is:

diagnostic: regular compiler diagnostics
artifact: artifact notifications
future_breakage: Future breakage report
unused_extern: Unused crate warnings/errors

This matches the "internally tagged" representation for serde enums.

Author: jsgf

compiler/rustc_errors/src/json.rs

@@ -138,6 +138,26 @@ impl JsonEmitter {
     pub fn ui_testing(self, ui_testing: bool) -> Self {
         Self { ui_testing, ..self }
     }
+
+    fn emit_typed(
+        &mut self,
+        ty: &str,
+        val: impl Serialize,
+    ) -> io::Result<()> {
+        let mut v = serde_json::to_value(val).unwrap();
+
+        // only attempt to type objects
+        if let Some(obj) = v.as_object_mut() {
+            obj.insert("type".to_string(), ty.into());
+        }
+
+        if self.pretty {
+            writeln!(self.dst, "{}", serde_json::to_string_pretty(&v).unwrap())
+        } else {
+            writeln!(self.dst, "{}", serde_json::to_string(&v).unwrap())
+        }
+        .and_then(|_| self.dst.flush())
+    }
 }
 
 impl Translate for JsonEmitter {
@@ -153,25 +173,15 @@ 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_typed("diagnostic", data);
         if let Err(e) = result {
             panic!("failed to print diagnostics: {e:?}");
         }
     }
 
     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_typed("artifact", data);
         if let Err(e) = result {
             panic!("failed to print notification: {e:?}");
         }
@@ -188,12 +198,7 @@ impl Emitter for JsonEmitter {
             })
             .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_typed("future_breakage", report);
         if let Err(e) = result {
             panic!("failed to print future breakage report: {e:?}");
         }
@@ -202,12 +207,7 @@ 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_typed("unused_extern", data);
         if let Err(e) = result {
             panic!("failed to print unused externs: {e:?}");
         }

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.
+{"children":[],"code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -24,17 +24,17 @@ This error occurs when an expression was used in a place where the compiler
 expected an expression of a different type. It can occur in several cases, the
 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":"$DIR/flag-json.rs","byte_start":243,"byte_end":245,"line_start":7,"line_end":7,"column_start":17,"column_end":19,"is_primary":true,"text":[{"text":"    let _: () = 42;","highlight_start":17,"highlight_end":19}],"label":"expected `()`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/flag-json.rs","byte_start":238,"byte_end":240,"line_start":7,"line_end":7,"column_start":12,"column_end":14,"is_primary":false,"text":[{"text":"    let _: () = 42;","highlight_start":12,"highlight_end":14}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"error[E0308]: mismatched types
+"},"level":"error","message":"mismatched types","rendered":"error[E0308]: mismatched types
   --> $DIR/flag-json.rs:7:17
    |
 LL | ..._: () = 42;
    |       --   ^^ expected `()`, found integer
    |       |
    |       expected due to this
 
-"}
-{"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
+","spans":[{"byte_end":245,"byte_start":243,"column_end":19,"column_start":17,"expansion":null,"file_name":"$DIR/flag-json.rs","is_primary":true,"label":"expected `()`, found integer","line_end":7,"line_start":7,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":19,"highlight_start":17,"text":"    let _: () = 42;"}]},{"byte_end":240,"byte_start":238,"column_end":14,"column_start":12,"expansion":null,"file_name":"$DIR/flag-json.rs","is_primary":false,"label":"expected due to this","line_end":7,"line_start":7,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":14,"highlight_start":12,"text":"    let _: () = 42;"}]}],"type":"diagnostic"}
+{"children":[],"code":null,"level":"error","message":"aborting due to previous error","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`.
-"}
+","spans":[],"type":"diagnostic"}
+{"children":[],"code":null,"level":"failure-note","message":"For more information about this error, try `rustc --explain E0308`.","rendered":"For more information about this error, try `rustc --explain E0308`.
+","spans":[],"type":"diagnostic"}

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.
+{"children":[{"children":[],"code":null,"level":"help","message":"try using a conversion method","rendered":null,"spans":[{"byte_end":622,"byte_start":622,"column_end":23,"column_start":23,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":null,"line_end":17,"line_start":17,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","text":[{"highlight_end":23,"highlight_start":23,"text":"    let s : String = 1;  // Error in the middle of line."}]}]}],"code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -24,9 +24,9 @@ This error occurs when an expression was used in a place where the compiler
 expected an expression of a different type. It can occur in several cases, the
 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.
+"},"level":"error","message":"mismatched types","rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:17:22: error[E0308]: mismatched types
+","spans":[{"byte_end":622,"byte_start":621,"column_end":23,"column_start":22,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":"expected `String`, found integer","line_end":17,"line_start":17,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":23,"highlight_start":22,"text":"    let s : String = 1;  // Error in the middle of line."}]},{"byte_end":618,"byte_start":612,"column_end":19,"column_start":13,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":false,"label":"expected due to this","line_end":17,"line_start":17,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":19,"highlight_start":13,"text":"    let s : String = 1;  // Error in the middle of line."}]}],"type":"diagnostic"}
+{"children":[{"children":[],"code":null,"level":"help","message":"try using a conversion method","rendered":null,"spans":[{"byte_end":682,"byte_start":682,"column_end":23,"column_start":23,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":null,"line_end":19,"line_start":19,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","text":[{"highlight_end":23,"highlight_start":23,"text":"    let s : String = 1"}]}]}],"code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -52,9 +52,9 @@ This error occurs when an expression was used in a place where the compiler
 expected an expression of a different type. It can occur in several cases, the
 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.
+"},"level":"error","message":"mismatched types","rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:19:22: error[E0308]: mismatched types
+","spans":[{"byte_end":682,"byte_start":681,"column_end":23,"column_start":22,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":"expected `String`, found integer","line_end":19,"line_start":19,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":23,"highlight_start":22,"text":"    let s : String = 1"}]},{"byte_end":678,"byte_start":672,"column_end":19,"column_start":13,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":false,"label":"expected due to this","line_end":19,"line_start":19,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":19,"highlight_start":13,"text":"    let s : String = 1"}]}],"type":"diagnostic"}
+{"children":[{"children":[],"code":null,"level":"help","message":"try using a conversion method","rendered":null,"spans":[{"byte_end":746,"byte_start":746,"column_end":2,"column_start":2,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":null,"line_end":23,"line_start":23,"suggested_replacement":".to_string()","suggestion_applicability":"MaybeIncorrect","text":[{"highlight_end":2,"highlight_start":2,"text":"1;  // Error after the newline."}]}]}],"code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -80,9 +80,9 @@ This error occurs when an expression was used in a place where the compiler
 expected an expression of a different type. It can occur in several cases, the
 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.
+"},"level":"error","message":"mismatched types","rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:23:1: error[E0308]: mismatched types
+","spans":[{"byte_end":746,"byte_start":745,"column_end":2,"column_start":1,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":"expected `String`, found integer","line_end":23,"line_start":23,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":2,"highlight_start":1,"text":"1;  // Error after the newline."}]},{"byte_end":741,"byte_start":735,"column_end":19,"column_start":13,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":false,"label":"expected due to this","line_end":22,"line_start":22,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":19,"highlight_start":13,"text":"    let s : String ="}]}],"type":"diagnostic"}
+{"children":[],"code":{"code":"E0308","explanation":"Expected type did not match the received type.
 
 Erroneous code examples:
 
@@ -108,7 +108,7 @@ This error occurs when an expression was used in a place where the compiler
 expected an expression of a different type. It can occur in several cases, the
 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":"$DIR/json-bom-plus-crlf-multifile-aux.rs:25:22: error[E0308]: mismatched types
-"}
-{"message":"aborting due to 4 previous errors","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to 4 previous errors
-"}
+"},"level":"error","message":"mismatched types","rendered":"$DIR/json-bom-plus-crlf-multifile-aux.rs:25:22: error[E0308]: mismatched types
+","spans":[{"byte_end":809,"byte_start":801,"column_end":6,"column_start":22,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":true,"label":"expected `String`, found `()`","line_end":26,"line_start":25,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":23,"highlight_start":22,"text":"    let s : String = ("},{"highlight_end":6,"highlight_start":1,"text":"    );  // Error spanning the newline."}]},{"byte_end":798,"byte_start":792,"column_end":19,"column_start":13,"expansion":null,"file_name":"$DIR/json-bom-plus-crlf-multifile-aux.rs","is_primary":false,"label":"expected due to this","line_end":25,"line_start":25,"suggested_replacement":null,"suggestion_applicability":null,"text":[{"highlight_end":19,"highlight_start":13,"text":"    let s : String = ("}]}],"type":"diagnostic"}
+{"children":[],"code":null,"level":"error","message":"aborting due to 4 previous errors","rendered":"error: aborting due to 4 previous errors
+","spans":[],"type":"diagnostic"}