cmd/go: clarify promotion of C warnings to errors

CL 23005 (back in 2016!) added logic to promote C compiler warnings to
errors when running on the Go builders.

CL 437298 kept the logic to promote warnings to errors on the
builders, but dropped the explanatory message, I believe
unintentionally. Indeed, now there isn't even a comment in the code
explaining what's going on.

This CL adds back an explanatory message to the printed output, which
also serves as a explanation in the code as to why we're checking
$GO_BUILDER_NAME.

Change-Id: I769c55d213f96f73d20a41ab926fb91e71a5a22c
Reviewed-on: https://go-review.googlesource.com/c/go/+/522775
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 64b0aae2672eb3469a3de7424cfbc3d0ee921e15..0312a58fc581b70261fee6051a228b7e57627780 100644 (file)
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -2683,7 +2683,11 @@ func (b *Builder) ccompile(a *Action, p *load.Package, outfile string, flags []s
                        }
                }
 
-               if err != nil || os.Getenv("GO_BUILDER_NAME") != "" {
+               if err == nil && os.Getenv("GO_BUILDER_NAME") != "" {
+                       output = append(output, "C compiler warning promoted to error on Go builders\n"...)
+                       err = errors.New("warning promoted to error")
+               }
+               if err != nil {
                        err = formatOutput(b.WorkDir, p.Dir, p.ImportPath, p.Desc(), b.processOutput(output))
                } else {
                        b.showOutput(a, p.Dir, p.Desc(), b.processOutput(output))