improve error message for failed fetch (fix #8702): print where to fi…

…le issues (URL if possible)

(cherry picked from commit b2844a9)
ref: #8711

base/pkg/read.jl

@@ -145,4 +145,11 @@ function free(inst::Dict=installed())
     return pkgs
 end
 
+function issue_url(pkg::String)
+    ispath(pkg,".git") || return ""
+    m = match(Git.GITHUB_REGEX, url(pkg))
+    m == nothing && return ""
+    return "https://github.com/" * m.captures[1] * "/issues"
+end
+
 end # module

base/pkg/write.jl

@@ -12,7 +12,12 @@ function fetch(pkg::String, sha1::String)
     Git.run(`fetch -q $(Cache.path(pkg)) $refspec`, dir=pkg)
     Git.iscommit(sha1, dir=pkg) && return
     f = Git.iscommit(sha1, dir=Cache.path(pkg)) ? "fetch" : "prefetch"
-    error("$pkg: $f failed to get commit $(sha1[1:10]), please file a bug")
+    url = Read.issue_url(pkg)
+    if isempty(url)
+        error("$pkg: $f failed to get commit $(sha1[1:10]), please file a bug report with the package author.")
+    else
+        error("$pkg: $f failed to get commit $(sha1[1:10]), please file an issue at $url")
+    end
 end
 
 function checkout(pkg::String, sha1::String)