go.bbclass: add do_unpack function to handle common cases

Go source trees have a particular structure, with all
sources located under ${GOROOT}/src/<import-path>.
The fetcher step implemented by the 'go get' command
automatically follows this structure, so we need
to do the same here.

Since most Go packages are hosted in git repositories,
this adds a custom do_unpack() function that sets
the destsuffix to match the expected directory structure,
for any git SRC_URIs that haven't had a destsuffix
explicitly set in the recipe.

This simplifies recipe writing for the most common
cases.

(From OE-Core rev: efcf6513b71021ea4bfe6fbaa326e6591dee487d)

Signed-off-by: Matt Madison <matt@madison.systems>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/go.bbclass

@@ -55,6 +55,24 @@ GO_INSTALL ?= "${GO_IMPORT}/..."
 
 B = "${WORKDIR}/build"
 
+python go_do_unpack() {
+    src_uri = (d.getVar('SRC_URI') or "").split()
+    if len(src_uri) == 0:
+        return
+
+    try:
+        fetcher = bb.fetch2.Fetch(src_uri, d)
+        for url in fetcher.urls:
+            if fetcher.ud[url].type == 'git':
+                if fetcher.ud[url].parm.get('destsuffix') is None:
+                    s_dirname = os.path.basename(d.getVar('S'))
+                    fetcher.ud[url].parm['destsuffix'] = os.path.join(s_dirname, 'src',
+                                                                      d.getVar('GO_IMPORT')) + '/'
+        fetcher.unpack(d.getVar('WORKDIR'))
+    except bb.fetch2.BBFetchException as e:
+        raise bb.build.FuncFailed(e)
+}
+
 go_do_configure() {
 	ln -snf ${S}/src ${B}/
 }
@@ -79,4 +97,4 @@ go_do_install() {
 	fi
 }
 
-EXPORT_FUNCTIONS do_configure do_compile do_install
+EXPORT_FUNCTIONS do_unpack do_configure do_compile do_install