go: Bunch of fixes when using excludedPackages and other bits

Few things going on in this commit:

Do not print "Building subPakage $pkg" message if actually going to skip the
package. This was confusing to me when I was trying to figure out how to set
excludedPackages and seeing the "Building subpackage $pkg" messages for
packages I wanted to skip. Turns out this messages was being printed before
checking if we actually wanted to build the package and not necessarily that my
excludedPackages was wrong.

Make go-packages look a little bit more like go-modules, by adding testdata to
the default list of excluded packages.

This commit also does some setup outside the buildGoDir function so that we
avoid checking `excludedPackages` for every package and cut down the number
of grep calls by half since we always want at least one grep for the default
excludedPackages, might as well just add to the patterns being checked.

Finally, adds documentation for usage of excludedPackages and subPackages. I
had to read the implementation to figure out how to correctly use these
function arguments since there was no documentation and different uses in the
code base. So this commit documents usage of the arguments.

doc/languages-frameworks/go.section.md

@@ -142,4 +142,8 @@ Removes the pre-existing vendor directory. This should only be used if the depen
 
 ### `subPackages` {#var-go-subPackages}
 
-Limits the builder from building child packages that have not been listed. If `subPackages` is not specified, all child packages will be built.
+Specified as a string or list of strings. Limits the builder from building child packages that have not been listed. If `subPackages` is not specified, all child packages will be built.
+
+### `excludedPackages` {#var-go-excludedPackages}
+
+Specified as a string or list of strings. Causes the builder to skip building child packages that match any of the provided values. If `excludedPackages` is not specified, all child packages will be built.

pkgs/development/go-modules/generic/default.nix

@@ -171,13 +171,20 @@ let
     buildPhase = args.buildPhase or ''
       runHook preBuild
 
+      exclude='\(/_\|examples\|Godeps\|testdata'
+      if [[ -n "$excludedPackages" ]]; then
+        IFS=' ' read -r -a excludedArr <<<$excludedPackages
+        printf -v excludedAlternates '%s\\|' "''${excludedArr[@]}"
+        excludedAlternates=''${excludedAlternates%\\|} # drop final \| added by printf
+        exclude+='\\|'"$excludedAlternates"
+      fi
+      exclude+='\)'
+
       buildGoDir() {
         local d; local cmd;
         cmd="$1"
         d="$2"
         . $TMPDIR/buildFlagsArray
-        echo "$d" | grep -q "\(/_\|examples\|Godeps\|testdata\)" && return 0
-        [ -n "$excludedPackages" ] && echo "$d" | grep -q "$excludedPackages" && return 0
         local OUT
         if ! OUT="$(go $cmd $buildFlags "''${buildFlagsArray[@]}" ''${tags:+-tags=${lib.concatStringsSep "," tags}} ''${ldflags:+-ldflags="$ldflags"} -v -p $NIX_BUILD_CORES $d 2>&1)"; then
           if ! echo "$OUT" | grep -qE '(no( buildable| non-test)?|build constraints exclude all) Go (source )?files'; then
@@ -214,6 +221,7 @@ let
           export NIX_BUILD_CORES=1
       fi
       for pkg in $(getGoDirs ""); do
+        grep -q "$exclude" <<<$pkg && continue
         echo "Building subPackage $pkg"
         buildGoDir install "$pkg"
       done

pkgs/development/go-packages/generic/default.nix

@@ -150,13 +150,20 @@ let
 
       runHook renameImports
 
+      exclude='\(/_\|examples\|Godeps\|testdata'
+      if [[ -n "$excludedPackages" ]]; then
+        IFS=' ' read -r -a excludedArr <<<$excludedPackages
+        printf -v excludedAlternates '%s\\|' "''${excludedArr[@]}"
+        excludedAlternates=''${excludedAlternates%\\|} # drop final \| added by printf
+        exclude+='\\|'"$excludedAlternates"
+      fi
+      exclude+='\)'
+
       buildGoDir() {
         local d; local cmd;
         cmd="$1"
         d="$2"
         . $TMPDIR/buildFlagsArray
-        echo "$d" | grep -q "\(/_\|examples\|Godeps\)" && return 0
-        [ -n "$excludedPackages" ] && echo "$d" | grep -q "$excludedPackages" && return 0
         local OUT
         if ! OUT="$(go $cmd $buildFlags "''${buildFlagsArray[@]}" ''${tags:+-tags=${lib.concatStringsSep "," tags}} ''${ldflags:+-ldflags="$ldflags"} -v -p $NIX_BUILD_CORES $d 2>&1)"; then
           if ! echo "$OUT" | grep -qE '(no( buildable| non-test)?|build constraints exclude all) Go (source )?files'; then
@@ -195,6 +202,8 @@ let
           export NIX_BUILD_CORES=1
       fi
       for pkg in $(getGoDirs ""); do
+        grep -q "$exclude" <<<$pkg && continue
+        echo "Building subPackage $pkg"
         buildGoDir install "$pkg"
       done
     '' + lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''