DEBUG-2334 require file presence for line probe

While testing manually I encountered an exception due to
a line probe missing the file. This should not happen
and such a configuration is not usable since we don't know
which file to instrument. Add extra guards and a unit test
to handle this case.

lib/datadog/di/probe.rb

@@ -47,6 +47,10 @@ def initialize(id:, type:,
           raise ArgumentError, "Probe contains both line number and method name: #{id}"
         end
 
+        if line_no && !file
+          raise ArgumentError, "Probe contains line number but not file: #{id}"
+        end
+
         if type_name && !method_name || method_name && !type_name
           raise ArgumentError, "Partial method probe definition: #{id}"
         end
@@ -103,7 +107,10 @@ def capture_snapshot?
       # method or for stack traversal purposes?), therefore we do not check
       # for file name/path presence here and just consider the line number.
       def line?
-        !line_no.nil?
+        # Constructor checks that file is given if line number is given,
+        # but for safety, check again here since we somehow got a probe with
+        # a line number but no file in the wild.
+        !!(file && line_no)
       end
 
       # Returns whether the probe is a method probe.

spec/datadog/di/probe_spec.rb

@@ -45,6 +45,18 @@
       end
     end
 
+    context 'line number given but file is not' do
+      let(:probe) do
+        described_class.new(id: "42", type: :log, line_no: 5)
+      end
+
+      it "raises ArgumentError" do
+        expect do
+          probe
+        end.to raise_error(ArgumentError, /Probe contains line number but not file/)
+      end
+    end
+
     context 'unsupported type' do
       let(:probe) do
         # LOG_PROBE is a valid type in RC probe specification but not
@@ -151,7 +163,7 @@
 
   describe "#line_no" do
     context "one line number" do
-      let(:probe) { described_class.new(id: "x", type: :log, line_no: 5) }
+      let(:probe) { described_class.new(id: "x", type: :log, file: 'x', line_no: 5) }
 
       it "returns the line number" do
         expect(probe.line_no).to eq 5
@@ -169,7 +181,7 @@
 
   describe "#line_no!" do
     context "one line number" do
-      let(:probe) { described_class.new(id: "x", type: :log, line_no: 5) }
+      let(:probe) { described_class.new(id: "x", type: :log, file: 'x', line_no: 5) }
 
       it "returns the line number" do
         expect(probe.line_no!).to eq 5