From 81898644e7126fc13a8a7084c647fc9f8c1830c2 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Tue, 19 May 2015 14:26:39 +0200
Subject: [PATCH 1/2] This commit removes the syntax diagnostic validation as
 it's been plaguing the bots for two separate reasons and needs a quick fix
 for now:

1. It's possible to read the stale metadata of previous builds, causing spurious
   failures that can only be solved by blowing away `tmp`.
2. The code does not currently handle concurrent compilations where JSON files
   in the metadata directory may be half-written and hence contain invalid JSON
   when read.

This validation should come back, but it should likely be part of a lint pass
run at the very end of the build that doesn't run into consistency or
concurrency problems.

----

This commit is a revised version of PR #25592; this approach differs
in that it continues to output the JSON metadata, so that the error
index page continues to work (assuming that people do not accidentally
put in duplicate entries in the meantime).
---
 src/libsyntax/diagnostics/plugin.rs | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index 16841bd903981..2579b3448cb73 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -14,7 +14,7 @@ use std::collections::BTreeMap;
 use ast;
 use ast::{Ident, Name, TokenTree};
 use codemap::Span;
-use diagnostics::metadata::{check_uniqueness, output_metadata, Duplicate};
+use diagnostics::metadata::{output_metadata};
 use ext::base::{ExtCtxt, MacEager, MacResult};
 use ext::build::AstBuilder;
 use parse::token;
@@ -158,19 +158,11 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
         _ => unreachable!()
     };
 
-    // Check uniqueness of errors and output metadata.
+    // Output metadata.
     with_registered_diagnostics(|diagnostics| {
-        match check_uniqueness(crate_name, &*diagnostics) {
-            Ok(Duplicate(err, location)) => {
-                ecx.span_err(span, &format!(
-                    "error {} from `{}' also found in `{}'",
-                    err, crate_name, location
-                ));
-            },
-            Ok(_) => (),
-            Err(e) => panic!("{}", e.description())
-        }
-
+        // FIXME (25364, 25592): used to ensure error code uniqueness
+        // here, but the approach employed was too brittle. Need to
+        // put such a check back in (e.g. in `make tidy`).
         output_metadata(&*ecx, crate_name, &*diagnostics).ok().expect("metadata output error");
     });
 

From 723d1df849986d619a8b433e01c1b17e43997335 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Thu, 21 May 2015 16:35:16 +0200
Subject: [PATCH 2/2] Provide more info when encountering error during error
 code metadata output.

---
 src/libsyntax/diagnostics/plugin.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index 2579b3448cb73..1808f51ac457a 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -10,6 +10,7 @@
 
 use std::cell::RefCell;
 use std::collections::BTreeMap;
+use std::error::Error;
 
 use ast;
 use ast::{Ident, Name, TokenTree};
@@ -163,7 +164,17 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
         // FIXME (25364, 25592): used to ensure error code uniqueness
         // here, but the approach employed was too brittle. Need to
         // put such a check back in (e.g. in `make tidy`).
-        output_metadata(&*ecx, crate_name, &*diagnostics).ok().expect("metadata output error");
+        match output_metadata(&*ecx, crate_name, &*diagnostics) {
+            Ok(()) => {}
+            Err(error) => {
+                ecx.span_err(span, &format!("metadata output error {}", error.description()));
+                let mut error: &Error = &*error;
+                while let Some(cause) = error.cause() {
+                    error = cause;
+                    ecx.span_err(span, &format!("caused by error {}", error.description()));
+                }
+            }
+        }
     });
 
     // Construct the output expression.