[clang-tidy] Add a fully custom message to bugprone-unsafe-functions (#162443)

In some cases, such as when recommending the compiler option
_FORTIFY_SOURCE, the current custom message format is clunky. Now, when
the reason starts with `>`, the replacement string is omitted., so only
the Reason is shown.

`^function$,,has a custom message;` - function 'function' has a custom
message; it should not be used
`^function$,,>has a custom message and no replacement suggestion;` -
function 'function' has a custom message and no replacement suggestion

---------

Co-authored-by: Donát Nagy <[email protected]>

Author: Discookie

clang-tools-extra/clang-tidy/bugprone/UnsafeFunctionsCheck.cpp

@@ -301,14 +301,20 @@ void UnsafeFunctionsCheck::check(const MatchFinder::MatchResult &Result) {
   if (Custom) {
     for (const auto &Entry : CustomFunctions) {
       if (Entry.Pattern.match(*FuncDecl)) {
-        const StringRef Reason =
+        StringRef Reason =
             Entry.Reason.empty() ? "is marked as unsafe" : Entry.Reason.c_str();
 
-        if (Entry.Replacement.empty()) {
+        // Omit the replacement, when a fully-custom reason is given.
+        if (Reason.consume_front(">")) {
+          diag(SourceExpr->getExprLoc(), "function %0 %1")
+              << FuncDecl << Reason.trim() << SourceExpr->getSourceRange();
+          // Do not recommend a replacement when it is not present.
+        } else if (Entry.Replacement.empty()) {
           diag(SourceExpr->getExprLoc(),
                "function %0 %1; it should not be used")
               << FuncDecl << Reason << Entry.Replacement
               << SourceExpr->getSourceRange();
+          // Otherwise, emit the replacement.
         } else {
           diag(SourceExpr->getExprLoc(),
                "function %0 %1; '%2' should be used instead")

clang-tools-extra/docs/ReleaseNotes.rst

@@ -69,6 +69,13 @@ Potentially Breaking Changes
   - `CharTypdefsToIgnore` to `CharTypedefsToIgnore` in
     :doc:`bugprone-signed-char-misuse
     <clang-tidy/checks/bugprone/signed-char-misuse>`
+  
+- Modified the custom message format of :doc:`bugprone-unsafe-functions
+  <clang-tidy/checks/bugprone/unsafe-functions>` by assigning a special meaning
+  to the character ``>`` at the start of the value of the option
+  ``CustomFunctions``. If the option value starts with ``>``, then the
+  replacement suggestion part of the message (which would be included by
+  default) is omitted. (This does not change the warning locations.)
 
 - :program:`clang-tidy` now displays warnings from all non-system headers by
   default. Previously, users had to explicitly opt-in to header warnings using
@@ -387,6 +394,11 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/unhandled-self-assignment>` check by adding
   an additional matcher that generalizes the copy-and-swap idiom pattern
   detection.
+  
+- Improved :doc:`bugprone-unsafe-functions
+  <clang-tidy/checks/bugprone/unsafe-functions>` check by hiding the default
+  suffix when the reason starts with the character `>` in the `CustomFunctions`
+  option.
 
 - Improved :doc:`cppcoreguidelines-avoid-non-const-global-variables
   <clang-tidy/checks/cppcoreguidelines/avoid-non-const-global-variables>` check

clang-tools-extra/docs/clang-tidy/checks/bugprone/unsafe-functions.rst

@@ -96,37 +96,62 @@ to be checked. The format is the following, without newlines:
 The functions are matched using POSIX extended regular expressions.
 *(Note: The regular expressions do not support negative* ``(?!)`` *matches.)*
 
-The `reason` is optional and is used to provide additional information
-about the reasoning behind the replacement. The default reason is
-`is marked as unsafe`.
+The ``reason`` is optional and is used to provide additional information about the
+reasoning behind the replacement. The default reason is ``is marked as unsafe``.
 
-If `replacement` is empty, the text `it should not be used` will be shown
-instead of the suggestion for a replacement.
+If ``replacement`` is empty, the default text ``it should not be used`` will be
+shown instead of the suggestion for a replacement.
 
-As an example, the configuration `^original$, replacement, is deprecated;`
-will produce the following diagnostic message.
+If the ``reason`` starts with the character ``>``, the reason becomes fully custom.
+The default suffix is disabled even if a ``replacement`` is present, and only the
+reason message is shown after the matched function, to allow better control over
+the suggestions. (The starting ``>`` and whitespace directly after it are
+trimmed from the message.)
+
+As an example, the following configuration matches only the function ``original``
+in the default namespace. A similar diagnostic can also be printed using a fully
+custom reason.
 
 .. code:: c
 
+   // bugprone-unsafe-functions.CustomFunctions:
+   //   ^original$, replacement, is deprecated;
+   // Using the fully custom message syntax:
+   //   ^suspicious$,,> should be avoided if possible.
    original(); // warning: function 'original' is deprecated; 'replacement' should be used instead.
+   suspicious(); // warning: function 'suspicious' should be avoided if possible.
    ::std::original(); // no-warning
    original_function(); // no-warning
 
-If the regular expression contains the character `:`, it is matched against the
-qualified name (i.e. ``std::original``), otherwise the regex is matched against the unqualified name (``original``).
-If the regular expression starts with `::` (or `^::`), it is matched against the
-fully qualified name (``::std::original``).
+If the regular expression contains the character ``:``, it is matched against the
+qualified name (i.e. ``std::original``), otherwise the regex is matched against
+the unqualified name (``original``). If the regular expression starts with ``::``
+(or ``^::``), it is matched against the fully qualified name
+(``::std::original``).
+
+One of the use cases for fully custom messages is suggesting compiler options
+and warning flags:
+
+.. code:: c
+
+   // bugprone-unsafe-functions.CustomFunctions:
+   //   ^memcpy$,,>is recommended to have compiler hardening using '_FORTIFY_SOURCE';
+   //   ^printf$,,>is recommended to have the '-Werror=format-security' compiler warning flag;
+
+   memcpy(dest, src, 999'999); // warning: function 'memcpy' is recommended to have compiler hardening using '_FORTIFY_SOURCE'
+   printf(raw_str); // warning: function 'printf' is recommended to have the '-Werror=format-security' compiler warning flag
 
 .. note::
 
-   Fully qualified names can contain template parameters on certain C++ classes, but not on C++ functions.
-   Type aliases are resolved before matching.
+   Fully qualified names can contain template parameters on certain C++ classes,
+   but not on C++ functions. Type aliases are resolved before matching.
 
    As an example, the member function ``open`` in the class ``std::ifstream``
    has a fully qualified name of ``::std::basic_ifstream<char>::open``.
 
-   The example could also be matched with the regex ``::std::basic_ifstream<[^>]*>::open``, which matches all potential
-   template parameters, but does not match nested template classes.
+   The example could also be matched with the regex
+   ``::std::basic_ifstream<[^>]*>::open``, which matches all potential template
+   parameters, but does not match nested template classes.
 
 Options
 -------

clang-tools-extra/test/clang-tidy/checkers/bugprone/unsafe-functions-custom.c

@@ -1,5 +1,5 @@
 // RUN: %check_clang_tidy -check-suffix=NON-STRICT-REGEX %s bugprone-unsafe-functions %t --\
-// RUN:   -config="{CheckOptions: {bugprone-unsafe-functions.CustomFunctions: '::name_match,replacement,is a qualname match;^::prefix_match,,is matched on qualname prefix'}}"
+// RUN:   -config="{CheckOptions: {bugprone-unsafe-functions.CustomFunctions: \"::name_match,,>is a qualname match, but with a fully 'custom' message;^::prefix_match,,is matched on qualname prefix\"}}"
 // RUN: %check_clang_tidy -check-suffix=STRICT-REGEX     %s bugprone-unsafe-functions %t --\
 // RUN:   -config="{CheckOptions: {bugprone-unsafe-functions.CustomFunctions: '^name_match$,replacement,is matched on function name only;^::prefix_match$,,is a full qualname match'}}"
 
@@ -11,14 +11,14 @@ void prefix_match_regex();
 
 void f1() {
   name_match();
-  // CHECK-MESSAGES-NON-STRICT-REGEX: :[[@LINE-1]]:3: warning: function 'name_match' is a qualname match; 'replacement' should be used instead
+  // CHECK-MESSAGES-NON-STRICT-REGEX: :[[@LINE-1]]:3: warning: function 'name_match' is a qualname match, but with a fully 'custom' message
   // CHECK-MESSAGES-STRICT-REGEX: :[[@LINE-2]]:3: warning: function 'name_match' is matched on function name only; 'replacement' should be used instead
   prefix_match();
   // CHECK-MESSAGES-NON-STRICT-REGEX: :[[@LINE-1]]:3: warning: function 'prefix_match' is matched on qualname prefix; it should not be used
   // CHECK-MESSAGES-STRICT-REGEX: :[[@LINE-2]]:3: warning: function 'prefix_match' is a full qualname match; it should not be used
 
   name_match_regex();
-  // CHECK-MESSAGES-NON-STRICT-REGEX: :[[@LINE-1]]:3: warning: function 'name_match_regex' is a qualname match; 'replacement' should be used instead
+  // CHECK-MESSAGES-NON-STRICT-REGEX: :[[@LINE-1]]:3: warning: function 'name_match_regex' is a qualname match, but with a fully 'custom' message
   // no-warning STRICT-REGEX
 
   prefix_match_regex();