[clang-tools-extra] [clang-tidy] Add new check bugprone-tagged-union-member-count (PR #89925)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,181 @@
+// RUN: %check_clang_tidy %s bugprone-tagged-union-member-count %t
+
+enum tags3 {
+	tags3_1,
+	tags3_2,
+	tags3_3,
+};
+
+enum tags4 {
+	tags4_1,
+	tags4_2,
+	tags4_3,
+	tags4_4,
+};
+
+enum tags5 {
+	tags5_1,
+	tags5_2,
+	tags5_3,
+	tags5_4,
+	tags5_5,
+};
+
+union union3 {
+	short *shorts;
+	int *ints;
+	float *floats;
+};
+
+union union4 {
+	short *shorts;
+	double *doubles;
+	int *ints;
+	float *floats;
+};
+
+// It is not obvious which enum is the tag for the union.
+struct taggedunion2 { // No warnings expected.
+	enum tags3 tagA;
+	enum tags4 tagB;
+	union union4 data;
+};
+
+// It is not obvious which union does the tag belong to.
+struct taggedunion4 { // No warnings expected.
+	enum tags3 tag;
+	union union3 dataB;
+	union union3 dataA;
+};
+
+struct taggedunion1 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum tags3 tag;
+    union union4 data;
+};
+
+struct taggedunion5 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum tags3 tag;
+    union {
+		int *ints;
+		char characters[13];
+		struct {
+			double re;
+			double im;
+		} complex;
+		long l;
+    } data;
+};
+
+struct taggedunion7 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum {
+		tag1,
+		tag2,
+		tag3,
+	} tag;
+	union union4 data;
+};
+
+struct taggedunion8 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum {
+		tag1,
+		tag2,
+		tag3,
+	} tag;
+	union {
+		int *ints;
+		char characters[13];
+		struct {
+			double re;
+			double im;
+		} complex;
+		long l;
+	} data;
+};
+
+struct nested1 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum tags3 tag;
+	union {
+		char c;
+		short s;
+		int i;
+		struct { // CHECK-MESSAGES: :[[@LINE]]:3: warning: Tagged union has fewer data members than tags! Data members: 4 Tags: 5 [bugprone-tagged-union-member-count]
+			enum tags5 tag;
+			union union4 data;
+		} inner;
+	} data;
+};
+
+struct nested2 {
+	enum tags3 tag;
+	union {
+		float f;
+		int i;
+		struct { // CHECK-MESSAGES: :[[@LINE]]:3: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+			enum tags3 tag;
+			union union4 data;
+		} inner;
+	} data;
+};
+
+struct nested3 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has fewer data members than tags! Data members: 2 Tags: 3 [bugprone-tagged-union-member-count]
+	enum tags3 tag;
+	union {
+		float f;
+		int i;
+		struct innerdecl { // CHECK-MESSAGES: :[[@LINE]]:10: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+			enum tags3 tag;
+			union union4 data;
+		}; 
+	} data;
+};
+
+enum tag_with_counter_lowercase {
+	node_type_loop,
+	node_type_branch,
+	node_type_function,
+	node_type_count,
+};
+
+enum tag_with_counter_uppercase {
+	NODE_TYPE_LOOP,
+	NODE_TYPE_BRANCH,
+	NODE_TYPE_FUNCTION,
+	NODE_TYPE_COUNT,
+};
+
+struct taggedunion10 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum tag_with_counter_lowercase tag;
+	union union4 data;
+};
+
+struct taggedunion11 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has more data members than tags! Data members: 4 Tags: 3 [bugprone-tagged-union-member-count]
+	enum tag_with_counter_uppercase tag;
+	union union4 data;
+};
+
+// Without the counter enum constant the number of tags
+// and the number data members are equal.
+struct taggedunion12 { // No warnings expected.
+	enum tag_with_counter_uppercase tag;
+	union union3 data;
+};
+
+// Technically this means that every enum value is defined from 0-256 and therefore a warning is given.
+enum mycolor {
+	mycolor_black = 0x00,
+	mycolor_gray  = 0xcc,
+	mycolor_white = 0xff,
+};
+
+struct taggedunion9 { // CHECK-MESSAGES: :[[@LINE]]:8: warning: Tagged union has fewer data members than tags! Data members: 3 Tags: 256 [bugprone-tagged-union-member-count]
+	enum mycolor tag;
+	union {
+		int a;
+		float b;
+		struct {
+			double re;
+			double im;
+		} complex;
+	} data;
+};
+
----------------
PiotrZSL wrote:

add tests with typedefs, where enum type is behind typedef, or union is behind typedef, this may require you to get "CanonicalType" of enum and record.

https://github.com/llvm/llvm-project/pull/89925