Remove more hasattr/getattr calls in go_context (#4054)

**What type of PR is this?**
starlark cleanup

**What does this PR do? Why is it needed?**
The current logic to grab all the providers is confusing; it runs the
fallback logics even in the case when `go_context_data` is found. Easier
to follow when we pass the data in explicitly, and a bit faster as well.

I also considered making a `go_context_v2` api that doesn't have all the
fallbacks and using that to power `go_context`, but didn't do it for
now.

**Which issues(s) does this PR fix?**

Fixes #

**Other notes for review**

Author: dzbarsky

go/private/context.bzl

@@ -381,7 +381,8 @@ def go_context(
         importpath = None,
         importmap = None,
         embed = None,
-        importpath_aliases = None):
+        importpath_aliases = None,
+        go_context_data = None):
     """Returns an API used to build Go code.
 
     See /go/toolchains.rst#go-context
@@ -390,26 +391,33 @@ def go_context(
         attr = ctx.attr
     toolchain = ctx.toolchains[GO_TOOLCHAIN]
     cgo_context_info = None
+    go_context_info = None
     go_config_info = None
     stdlib = None
-    coverdata = None
-    nogo = None
-    if hasattr(attr, "_go_context_data"):
-        go_context_data = _flatten_possibly_transitioned_attr(attr._go_context_data)
+
+    if go_context_data == None:
+        if hasattr(attr, "_go_context_data"):
+            go_context_data = _flatten_possibly_transitioned_attr(attr._go_context_data)
+            if CgoContextInfo in go_context_data:
+                cgo_context_info = go_context_data[CgoContextInfo]
+            go_config_info = go_context_data[GoConfigInfo]
+            stdlib = go_context_data[GoStdLib]
+            go_context_info = go_context_data[GoContextInfo]
+        if getattr(attr, "_cgo_context_data", None) and CgoContextInfo in attr._cgo_context_data:
+            cgo_context_info = attr._cgo_context_data[CgoContextInfo]
+        if getattr(attr, "cgo_context_data", None) and CgoContextInfo in attr.cgo_context_data:
+            cgo_context_info = attr.cgo_context_data[CgoContextInfo]
+        if hasattr(attr, "_go_config"):
+            go_config_info = attr._go_config[GoConfigInfo]
+        if hasattr(attr, "_stdlib"):
+            stdlib = _flatten_possibly_transitioned_attr(attr._stdlib)[GoStdLib]
+    else:
+        go_context_data = _flatten_possibly_transitioned_attr(go_context_data)
         if CgoContextInfo in go_context_data:
             cgo_context_info = go_context_data[CgoContextInfo]
         go_config_info = go_context_data[GoConfigInfo]
         stdlib = go_context_data[GoStdLib]
-        coverdata = go_context_data[GoContextInfo].coverdata
-        nogo = go_context_data[GoContextInfo].nogo
-    if getattr(attr, "_cgo_context_data", None) and CgoContextInfo in attr._cgo_context_data:
-        cgo_context_info = attr._cgo_context_data[CgoContextInfo]
-    if getattr(attr, "cgo_context_data", None) and CgoContextInfo in attr.cgo_context_data:
-        cgo_context_info = attr.cgo_context_data[CgoContextInfo]
-    if hasattr(attr, "_go_config"):
-        go_config_info = attr._go_config[GoConfigInfo]
-    if hasattr(attr, "_stdlib"):
-        stdlib = _flatten_possibly_transitioned_attr(attr._stdlib)[GoStdLib]
+        go_context_info = go_context_data[GoContextInfo]
 
     mode = get_mode(ctx, toolchain, cgo_context_info, go_config_info)
 
@@ -515,8 +523,8 @@ def go_context(
         importpath_aliases = importpath_aliases,
         pathtype = pathtype,
         cgo_tools = cgo_tools,
-        nogo = nogo,
-        coverdata = coverdata,
+        nogo = go_context_info.nogo if go_context_info else None,
+        coverdata = go_context_info.coverdata if go_context_info else None,
         coverage_enabled = ctx.configuration.coverage_enabled,
         coverage_instrumented = ctx.coverage_instrumented(),
         env = env,

go/private/rules/binary.bzl

@@ -115,7 +115,13 @@ _go_cc_aspect = aspect(
 
 def _go_binary_impl(ctx):
     """go_binary_impl emits actions for compiling and linking a go executable."""
-    go = go_context(ctx, include_deprecated_properties = False)
+    go = go_context(
+        ctx,
+        include_deprecated_properties = False,
+        importpath = ctx.attr.importpath,
+        embed = ctx.attr.embed,
+        go_context_data = ctx.attr._go_context_data,
+    )
 
     is_main = go.mode.link not in (LINKMODE_SHARED, LINKMODE_PLUGIN)
     library = go.new_library(go, importable = False, is_main = is_main)

go/private/rules/library.bzl

@@ -39,8 +39,11 @@ def _go_library_impl(ctx):
         include_deprecated_properties = False,
         importpath = ctx.attr.importpath,
         importmap = ctx.attr.importmap,
+        importpath_aliases = ctx.attr.importpath_aliases,
         embed = ctx.attr.embed,
+        go_context_data = ctx.attr._go_context_data,
     )
+
     library = go.new_library(go)
     source = go.library_to_source(go, ctx.attr, library, ctx.coverage_instrumented())
     archive = go.archive(go, source)
@@ -204,8 +207,22 @@ go_library = rule(
 
 # See docs/go/core/rules.md#go_library for full documentation.
 
+def _go_tool_library_impl(ctx):
+    """Implements the go_tool_library() rule."""
+    go = go_context(ctx, include_deprecated_properties = False)
+
+    library = go.new_library(go)
+    source = go.library_to_source(go, ctx.attr, library, ctx.coverage_instrumented())
+    archive = go.archive(go, source)
+
+    return [
+        library,
+        source,
+        archive,
+    ]
+
 go_tool_library = rule(
-    _go_library_impl,
+    _go_tool_library_impl,
     attrs = {
         "data": attr.label_list(allow_files = True),
         "srcs": attr.label_list(allow_files = True),

go/private/rules/test.bzl

@@ -56,7 +56,13 @@ def _go_test_impl(ctx):
     It emits an action to run the test generator, and then compiles the
     test into a binary."""
 
-    go = go_context(ctx, include_deprecated_properties = False)
+    go = go_context(
+        ctx,
+        include_deprecated_properties = False,
+        importpath = ctx.attr.importpath,
+        embed = ctx.attr.embed,
+        go_context_data = ctx.attr._go_context_data,
+    )
 
     # Compile the library to test with internal white box tests
     internal_library = go.new_library(go, testfilter = "exclude")