cswrap-core: skip known wrappers while invoking an analyzer

We want to hook `gcc -fanalyzer` on `clang` if `clang` is used as the
system compiler.  However, it does not make sense to hook GCC Analyzer
on `clang --analyze`, which is invoked by `csclng` while wrapping `gcc`
as the system compiler.

Apart from wasting resources by running multiple processes of GCC
Analyzer in parallel, this was causing unnecessary noise in `scan.log`
as GCC Analyzer complained about unsupported flags, which were injected
by `csclng` for `clang --analyze` only:
```
gcc: error: unrecognized command-line option ‘-fno-caret-diagnostics’
gcc: error: unrecognized command-line option ‘-fno-caret-diagnostics’
gcc: error: unrecognized command-line option ‘-fno-caret-diagnostics’
```

Reported-by: Lukáš Zaoral
Fixes: commit 983b895
Related: #43
Closes: #44

src/CMakeLists.txt

@@ -88,8 +88,9 @@ macro(add_cs_executable name sources)
     string(REGEX REPLACE "\\+\\+$" "" name_upper ${name_upper})
 
     if(PATH_TO_${name_upper})
-        target_compile_definitions(${name}
-            PRIVATE -DPATH_TO_${name_upper}=${PATH_TO_${name_upper}})
+        set(def -DPATH_TO_${name_upper}=${PATH_TO_${name_upper}})
+        target_compile_definitions(cswrap PRIVATE ${def})
+        target_compile_definitions(${name} PRIVATE ${def})
     endif()
 
     install(TARGETS ${name} DESTINATION ${CMAKE_INSTALL_BINDIR})

src/cswrap-core.c

@@ -366,6 +366,61 @@ static bool read_custom_opts(char **dst, const char *str)
     }
 }
 
+#if defined(PATH_TO_CSCLNG) || defined(PATH_TO_CSGCCA) \
+    || defined(PATH_TO_CSMATCH) || defined(PATH_TO_CSCPPC)
+/* if `path` starts with `prefix`, remove the prefix and the trailing ':' */
+static bool remove_path_prefix(char *path, const char *prefix)
+{
+    const size_t prefix_len = strlen(prefix);
+    if (strncmp(path, prefix, prefix_len))
+        // prefix not found
+        return false;
+
+    // skip all ':' that follow the prefix
+    const char *end = path + prefix_len;
+    while (*end == ':')
+        ++end;
+
+    // remove the prefix, including the trailing double dots
+    const size_t new_size = strlen(end) + /* NUL */ 1;
+    memmove(path, end, new_size);
+    return true;
+}
+
+/* if `path` starts with path to a known wrapper, remove the prefix */
+static bool remove_known_wrapper_from_path(char *path)
+{
+    bool removed = false;
+#ifdef PATH_TO_CSCLNG
+    removed |= remove_path_prefix(path, PATH_TO_CSCLNG);
+#endif
+#ifdef PATH_TO_CSGCCA
+    removed |= remove_path_prefix(path, PATH_TO_CSGCCA);
+#endif
+#ifdef PATH_TO_CSMATCH
+    removed |= remove_path_prefix(path, PATH_TO_CSMATCH);
+#endif
+#ifdef PATH_TO_CSCPPC
+    removed |= remove_path_prefix(path, PATH_TO_CSCPPC);
+#endif
+    return removed;
+}
+
+/* remove paths to known wrappers from the beginning of $PATH */
+static void sanitize_path_for_analyzer(void)
+{
+    char *path = getenv("PATH");
+    if (!path || !*path)
+        return;
+
+    /* the `path` string will be modified in place */
+    while (remove_known_wrapper_from_path(path))
+        ;
+}
+#else
+#   define sanitize_path_for_analyzer()
+#endif
+
 static void consider_running_analyzer(
         const int                   argc_orig,
         char **const                argv_orig)
@@ -437,6 +492,7 @@ static void consider_running_analyzer(
     }
 
     /* try to start analyzer */
+    sanitize_path_for_analyzer();
     pid_analyzer = launch_tool(analyzer_name_actual, argv, /* del_args */ NULL);
 
     /* FIXME: release also the memory allocated by asprintf() and