Remove error diagnostics uniqueness check and .json generation.

This is meant to be a temporary measure to get the builds to be
reliable again; see also Issue #25705.

mk/docs.mk

@@ -77,7 +77,8 @@ ERR_IDX_GEN = $(RPATH_VAR2_T_$(CFG_BUILD)_H_$(CFG_BUILD)) $(ERR_IDX_GEN_EXE)
 
 D := $(S)src/doc
 
-DOC_TARGETS := trpl style error-index
+# FIXME (#25705) eventually may want to put error-index target back here.
+DOC_TARGETS := trpl style
 COMPILER_DOC_TARGETS :=
 DOC_L10N_TARGETS :=
 

src/libsyntax/diagnostics/plugin.rs

@@ -14,7 +14,6 @@ use std::collections::BTreeMap;
 use ast;
 use ast::{Ident, Name, TokenTree};
 use codemap::Span;
-use diagnostics::metadata::{check_uniqueness, output_metadata, Duplicate};
 use ext::base::{ExtCtxt, MacEager, MacResult};
 use ext::build::AstBuilder;
 use parse::token;
@@ -148,7 +147,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
                                           token_tree: &[TokenTree])
                                           -> Box<MacResult+'cx> {
     assert_eq!(token_tree.len(), 3);
-    let (crate_name, name) = match (&token_tree[0], &token_tree[2]) {
+    let (_crate_name, name) = match (&token_tree[0], &token_tree[2]) {
         (
             // Crate name.
             &ast::TtToken(_, token::Ident(ref crate_name, _)),
@@ -158,21 +157,9 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
         _ => unreachable!()
     };
 
-    // Check uniqueness of errors and 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())
-        }
-
-        output_metadata(&*ecx, crate_name, &*diagnostics).ok().expect("metadata output error");
-    });
+    // FIXME (#25705): we used to ensure error code uniqueness and
+    // output error description JSON metadata here, but the approach
+    // employed was too brittle.
 
     // Construct the output expression.
     let (count, expr) =