fix(rust): fix panic when 'dependencies' field is not used in cargo.toml (#3997)

Author: DmitriyLewen

pkg/fanal/analyzer/language/rust/cargo/cargo.go

@@ -176,7 +176,11 @@ func (a cargoAnalyzer) parseCargoTOML(fsys fs.FS, path string) (map[string]strin
 		return nil, xerrors.Errorf("toml decode error: %w", err)
 	}
 
-	dependencies := tomlFile.Dependencies
+	// There are cases when toml file doesn't include `Dependencies` field (then map will be nil).
+	// e.g. when only `workspace.Dependencies` are used
+	// declare `dependencies` to avoid panic
+	dependencies := Dependencies{}
+	maps.Copy(dependencies, tomlFile.Dependencies)
 
 	// https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#platform-specific-dependencies
 	for _, target := range tomlFile.Target {
@@ -186,7 +190,7 @@ func (a cargoAnalyzer) parseCargoTOML(fsys fs.FS, path string) (map[string]strin
 	// https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#inheriting-a-dependency-from-a-workspace
 	maps.Copy(dependencies, tomlFile.Workspace["dependencies"])
 
-	for name, value := range tomlFile.Dependencies {
+	for name, value := range dependencies {
 		switch ver := value.(type) {
 		case string:
 			// e.g. regex = "1.5"

pkg/fanal/analyzer/language/rust/cargo/cargo_test.go

@@ -92,6 +92,27 @@ func Test_cargoAnalyzer_Analyze(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "Cargo.toml doesn't include `Dependencies` field",
+			dir:  "testdata/toml-only-workspace-deps",
+			want: &analyzer.AnalysisResult{
+				Applications: []types.Application{
+					{
+						Type:     types.Cargo,
+						FilePath: "Cargo.lock",
+						Libraries: []types.Package{
+							{
+								ID:        "[email protected]",
+								Name:      "memchr",
+								Version:   "2.5.0",
+								Indirect:  false,
+								Locations: []types.Location{{StartLine: 11, EndLine: 15}},
+							},
+						},
+					},
+				},
+			},
+		},
 		{
 			name: "no Cargo.toml",
 			dir:  "testdata/no-cargo-toml",

pkg/fanal/analyzer/language/rust/cargo/testdata/toml-only-workspace-deps/Cargo.lock

@@ -0,0 +1,9 @@
+[package]
+name = "app"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[workspace.dependencies]
+memchr = "2.5"