[clang-tools-extra] [clang-tidy] Add bugprone-macro-condition check (PR #210768)

[Richard Thomson via cfe-commits]

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+.. title:: clang-tidy - bugprone-macro-condition
+
+bugprone-macro-condition
+========================
+
+Warns about inconsistent macro usage in preprocessor conditions.
+
+Given the following code:
+
+.. code-block:: c++
+
+  #define USE_FOO 0
+  // ...
+  #if defined(USE_FOO)
+    // ...
+  #endif
+
+Here `USE_FOO` is defined to a value that would evaluate to false in a
+preprocessor condition, but checked for definition and not for its value.
+Was the intention to evaluate `USE_FOO` for a `true` expression, or was
+the intention to merely check whether or not the macro was defined?
+
+If the code later contains:
+
+.. code-block:: c++
+
+  #if USE_FOO
+    // ...
+  #endif
+
+Then the suspicions are raised further.
+
+The following scenarios result in warnings; no fixes
+are offered as the scenarios are all ambiguous.
----------------
LegalizeAdulthood wrote:

I've added documentation that I think addresses this.

https://github.com/llvm/llvm-project/pull/210768