[engine] Accept None for optional args to ctx.emit.finding

This will enable simpler integration with certain linting tools that
emit output that then needs to be translated to shac's finding schema.
E.g. some linting tools emit JSON output that omits empty fields, or
sets their values to null, so it's handy to be able to do `replacements
= output.get("replacements")` and have it "just work" even if
`replacements` is not set or is null.

Change-Id: I53ffcb3fb4d64081a13cc55f72343c9eff0eef9f
Reviewed-on: https://fuchsia-review.googlesource.com/c/shac-project/shac/+/929632
Commit-Queue: Auto-Submit <[email protected]>
Fuchsia-Auto-Submit: Oliver Newman <[email protected]>
Reviewed-by: Anthony Fandrianto <[email protected]>

internal/engine/run_test.go

@@ -2102,6 +2102,20 @@ func TestTestDataEmit(t *testing.T) {
 			nil,
 			"a check failed",
 		},
+		{
+			"ctx-emit-finding-none.star",
+			[]finding{
+				{
+					Check:   "cb",
+					Level:   Error,
+					Message: "bad code",
+					Root:    root,
+					File:    "file.txt",
+				},
+			},
+			nil,
+			"a check failed",
+		},
 		{
 			"ctx-emit-finding.star",
 			[]finding{

internal/engine/runtime_ctx_emit.go

@@ -41,11 +41,15 @@ func ctxEmitFinding(ctx context.Context, s *shacState, name string, args starlar
 		"level", &arglevel,
 		"message?", &argmessage,
 		"filepath?", &argfilepath,
-		"line?", &argline,
-		"col?", &argcol,
-		"end_line?", &argendLine,
-		"end_col?", &argendCol,
-		"replacements?", &argreplacements,
+		// The following arguments all use ?? so that None is interpreted the
+		// same as the argument being unset. This makes it easier to implement
+		// checks that run tools that emit JSON output that may contain null
+		// fields.
+		"line??", &argline,
+		"col??", &argcol,
+		"end_line??", &argendLine,
+		"end_col??", &argendCol,
+		"replacements??", &argreplacements,
 	); err != nil {
 		return err
 	}

internal/engine/testdata/emit/ctx-emit-finding-none.star

@@ -0,0 +1,27 @@
+# Copyright 2023 The Shac Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+def cb(ctx):
+    ctx.emit.finding(
+        level = "error",
+        message = "bad code",
+        filepath = "file.txt",
+        line = None,
+        col = None,
+        end_line = None,
+        end_col = None,
+        replacements = None,
+    )
+
+shac.register_check(cb)

internal/engine/version.go

@@ -26,7 +26,7 @@ var (
 	// Version is the current tool version.
 	//
 	// TODO(maruel): Add proper version, preferably from git tag.
-	Version = shacVersion{0, 1, 13}
+	Version = shacVersion{0, 1, 14}
 )
 
 func (v shacVersion) String() string {