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[rustc.git] / src / doc / rustc-dev-guide / src / rustc-driver-getting-diagnostics.md

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+# Example: Getting diagnostic through `rustc_interface`
+
+`rustc_interface` allows you to intercept diagnostics that would otherwise be printed to stderr.
+
+## Getting diagnostics
+
+To get diagnostics from the compiler, 
+configure `rustc_interface::Config` to output diagnostic to a buffer, 
+and run `TyCtxt.analysis`:
+
+```rust
+// See https://github.com/rust-lang/rustc-dev-guide/blob/master/examples/rustc-driver-getting-diagnostics.rs for complete program.
+let buffer = sync::Arc::new(sync::Mutex::new(Vec::new()));
+let config = rustc_interface::Config {
+    opts: config::Options {
+        // Configure the compiler to emit diagnostics in compact JSON format.
+        error_format: config::ErrorOutputType::Json {
+            pretty: false,
+            json_rendered: rustc_errors::emitter::HumanReadableErrorType::Default(
+                rustc_errors::emitter::ColorConfig::Never,
+            ),
+        },
+        /* other config */
+    },
+    // Redirect the diagnostic output of the compiler to a buffer.
+    diagnostic_output: rustc_session::DiagnosticOutput::Raw(Box::from(DiagnosticSink(
+        buffer.clone(),
+    ))),
+    /* other config */
+};
+rustc_interface::run_compiler(config, |compiler| {
+    compiler.enter(|queries| {
+        queries.global_ctxt().unwrap().take().enter(|tcx| {
+            // Run the analysis phase on the local crate to trigger the type error.
+            tcx.analysis(rustc_hir::def_id::LOCAL_CRATE);
+        });
+    });
+});
+// Read buffered diagnostics.
+let diagnostics = String::from_utf8(buffer.lock().unwrap().clone()).unwrap();
+```