From 457e4e7145abb897227ad5cca62ead6b41873983 Mon Sep 17 00:00:00 2001
From: Austin Schuh <austin.linux@gmail.com>
Date: Mon, 17 Jun 2019 12:02:06 -0700
Subject: [PATCH 1/3] Blacklist more cgo breaking warnings

Change-Id: Iae834f2cc179220c9c3f71f4f39a8be6edb79dc5
---
 go/private/context.bzl | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/go/private/context.bzl b/go/private/context.bzl
index 46ff54b8bb..33eecb5b0b 100644
--- a/go/private/context.bzl
+++ b/go/private/context.bzl
@@ -70,6 +70,8 @@ _GoContextData = provider()
 
 _COMPILER_OPTIONS_BLACKLIST = {
     "-fcolor-diagnostics": None,
+    "-fdiagnostics-color": None,
+    "-fmax-errors=20": None,
     "-Wall": None,
 
     # Symbols are needed by Go, so keep them

From a2c8859be9769f00bcd9591f58d99812ca6b875d Mon Sep 17 00:00:00 2001
From: Austin Schuh <austin.linux@gmail.com>
Date: Mon, 17 Jun 2019 12:02:32 -0700
Subject: [PATCH 2/3] Remove unused variable warnings from _cgo_main.c
 compilation

Change-Id: I78d0b0b96dcaa11783e76218e142878452aa6d1e
---
 go/private/rules/cgo.bzl | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/go/private/rules/cgo.bzl b/go/private/rules/cgo.bzl
index c4370909a3..abe91c3fc5 100644
--- a/go/private/rules/cgo.bzl
+++ b/go/private/rules/cgo.bzl
@@ -795,7 +795,10 @@ def setup_cgo_library_for_mode(name, srcs, cdeps, copts, cxxopts, cppopts, clink
         name = cgo_o_name,
         srcs = [select_main_c],
         deps = cdeps + cgo_o_deps,
-        copts = copts + cppopts,
+        copts = copts + cppopts + [
+            # The generated thunks often contain unused variables.
+            "-Wno-unused-variable",
+        ],
         linkopts = clinkopts,
         visibility = ["//visibility:private"],
         **common_attrs

From 2da4b47e143d4cbb10a6f5529b0afb62a87e16e7 Mon Sep 17 00:00:00 2001
From: Austin Schuh <austin.linux@gmail.com>
Date: Tue, 18 Jun 2019 14:33:29 -0700
Subject: [PATCH 3/3] Support arbitrary -fmax-errors=

Not everyone uses a -fmax-errors=20.  We can be more general.

Change-Id: Ic8c50bb08f32fe468f775c49c94534fb73899bae
---
 go/private/context.bzl | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/go/private/context.bzl b/go/private/context.bzl
index 33eecb5b0b..e9ab9d56cc 100644
--- a/go/private/context.bzl
+++ b/go/private/context.bzl
@@ -69,9 +69,15 @@ GoContext = provider()
 _GoContextData = provider()
 
 _COMPILER_OPTIONS_BLACKLIST = {
+    # cgo parses the error messages from the compiler.  It can't handle colors.
+    # Ignore both variants of the diagnostics color flag.
     "-fcolor-diagnostics": None,
     "-fdiagnostics-color": None,
-    "-fmax-errors=20": None,
+
+    # cgo also wants to see all the errors when it is testing the compiler.
+    # fmax-errors limits that and causes build failures.
+    "-fmax-errors=": None,
+
     "-Wall": None,
 
     # Symbols are needed by Go, so keep them
@@ -88,8 +94,18 @@ _LINKER_OPTIONS_BLACKLIST = {
     "-Wl,--gc-sections": None,
 }
 
+def _match_option(option, pattern):
+    if pattern.endswith("="):
+        return option.startswith(pattern)
+    else:
+        return option == pattern
+
 def _filter_options(options, blacklist):
-    return [option for option in options if option not in blacklist]
+    return [
+        option
+        for option in options
+        if not any([_match_option(option, pattern) for pattern in blacklist])
+    ]
 
 def _child_name(go, path, ext, name):
     childname = mode_string(go.mode) + "/"