Tidy up computation of import paths

Right now you see that jsonnet_to_json() and jsonnet_to_json_test()
implicitly call jsonnet with "-J .". This means that if these rules are
used in combination with libraries that are declared in the root module,
everything works as expected. But as soon as libraries are used from
other modules, importing them becomes more tedious.

The goal of this change is to ensure that if a Jsonnet project can be
built within the root module, that module can also safely be used as a
child module. We solve this by automatically adding the workspace root
to the set of import paths for which one or more source files exist.
Furthermore, by considering the root of every source file, we no longer
need to use bin_dir and genfiles_dir.

Fixes: #44
Fixes: #86
Fixed: #139
Fixes: #154
Fixes: #178

examples/.bazelignore

@@ -0,0 +1 @@
+other_module

examples/BUILD

@@ -247,3 +247,15 @@ jsonnet_to_json_test(
     output_file_contents = False,
     deps = [":workflow"],
 )
+
+jsonnet_to_json_test(
+    name = "other_module_test",
+    src = "other_module.jsonnet",
+    canonicalize_golden = False,
+    extra_args = ["--string"],
+    golden = "other_module_golden.txt",
+    deps = [
+        "@other_module//:hello",
+        "@other_module//:world",
+    ],
+)

examples/MODULE.bazel

@@ -8,3 +8,9 @@ local_path_override(
     module_name = "rules_jsonnet",
     path = "..",
 )
+
+bazel_dep(name = "other_module", version = "0.0.0")
+local_path_override(
+    module_name = "other_module",
+    path = "other_module",
+)

examples/other_module.jsonnet

@@ -0,0 +1 @@
+(import 'hello.jsonnet') + ' ' + (import 'world.jsonnet')

examples/other_module/BUILD.bazel

@@ -0,0 +1,19 @@
+load("@rules_jsonnet//jsonnet:jsonnet.bzl", "jsonnet_library")
+
+jsonnet_library(
+    name = "hello",
+    srcs = ["hello.jsonnet"],
+    visibility = ["//visibility:public"],
+)
+
+genrule(
+    name = "world_src",
+    outs = ["world.jsonnet"],
+    cmd = "echo \\'world\\' > $@",
+)
+
+jsonnet_library(
+    name = "world",
+    srcs = ["world.jsonnet"],
+    visibility = ["//visibility:public"],
+)

examples/other_module/MODULE.bazel

@@ -0,0 +1,6 @@
+module(
+    name = "other_module",
+    version = "0.0.0",
+)
+
+bazel_dep(name = "rules_jsonnet", version = "0.5.0")

examples/other_module/hello.jsonnet

@@ -0,0 +1 @@
+'hello'

examples/other_module_golden.txt

@@ -0,0 +1 @@
+hello world

jsonnet/jsonnet.bzl

@@ -51,6 +51,8 @@ jsonnet_go_dependencies()
 ```
 """
 
+load("@bazel_skylib//lib:paths.bzl", "paths")
+load("@bazel_skylib//lib:shell.bzl", "shell")
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
 _JSONNET_FILETYPE = [
@@ -59,13 +61,17 @@ _JSONNET_FILETYPE = [
     ".json",
 ]
 
-def _add_prefix_to_imports(label, imports):
-    imports_prefix = ""
-    if label.workspace_root:
-        imports_prefix += label.workspace_root + "/"
-    if label.package:
-        imports_prefix += label.package + "/"
-    return [imports_prefix + im for im in imports]
+def _get_import_paths(label, files, imports):
+    return [
+        # Implicitly add the workspace root as an import path.
+        paths.join(".", file.root.path, label.workspace_root)
+        for file in files
+    ] + [
+        # Explicitly provided import paths.
+        paths.join(".", file.root.path, label.workspace_root, label.package, im)
+        for file in files
+        for im in imports
+    ]
 
 def _setup_deps(deps):
     """Collects source files and import flags of transitive dependencies.
@@ -97,7 +103,10 @@ def _jsonnet_library_impl(ctx):
     """Implementation of the jsonnet_library rule."""
     depinfo = _setup_deps(ctx.attr.deps)
     sources = depset(ctx.files.srcs, transitive = [depinfo.transitive_sources])
-    imports = depset(_add_prefix_to_imports(ctx.label, ctx.attr.imports), transitive = [depinfo.imports])
+    imports = depset(
+        _get_import_paths(ctx.label, ctx.files.srcs, ctx.attr.imports),
+        transitive = [depinfo.imports],
+    )
     transitive_data = depset(
         transitive = [dep.data_runfiles.files for dep in ctx.attr.deps],
     )
@@ -210,12 +219,10 @@ def _jsonnet_to_json_impl(ctx):
         [
             "set -e;",
             toolchain.jsonnet_path,
-        ] + ["-J %s" % im for im in _add_prefix_to_imports(ctx.label, ctx.attr.imports)] +
-        ["-J %s" % im for im in depinfo.imports.to_list()] + [
-            "-J .",
-            "-J %s" % ctx.genfiles_dir.path,
-            "-J %s" % ctx.bin_dir.path,
-        ] + other_args +
+        ] +
+        ["-J " + shell.quote(im) for im in _get_import_paths(ctx.label, [ctx.file.src], ctx.attr.imports)] +
+        ["-J " % shell.quote(im) for im in depinfo.imports.to_list()] +
+        other_args +
         ["--ext-str %s=%s" %
          (_quote(key), _quote(val)) for key, val in jsonnet_ext_strs.items()] +
         ["--ext-str '%s'" %
@@ -385,8 +392,8 @@ def _jsonnet_to_json_test_impl(ctx):
     other_args = ctx.attr.extra_args + (["-y"] if ctx.attr.yaml_stream else [])
     jsonnet_command = " ".join(
         ["OUTPUT=$(%s" % ctx.executable.jsonnet.short_path] +
-        ["-J %s" % im for im in _add_prefix_to_imports(ctx.label, ctx.attr.imports)] +
-        ["-J %s" % im for im in depinfo.imports.to_list()] + ["-J ."] +
+        ["-J " + shell.quote(im) for im in _get_import_paths(ctx.label, [ctx.file.src], ctx.attr.imports)] +
+        ["-J " + shell.quote(im) for im in depinfo.imports.to_list()] +
         other_args +
         ["--ext-str %s=%s" %
          (_quote(key), _quote(val)) for key, val in jsonnet_ext_strs.items()] +