Add unique kwarg to CheckLibs

Minor tweak to CheckFunc - the dummy prototype should have
a dummy arg list too (comment from Python setuptools discussion).
Might as well fail the official way: #error instead of C syntax error.

Fixes #2768

Signed-off-by: Mats Wichmann <mats@linux.com>

6 files changed, 128 insertions, 41 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 93be68dfd..f51f8b228 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -124,6 +124,9 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
       based on what is known now, 3.12 itself should work with this release.
     - Add "append" keyword argument to Configure context's CheckLib and
       CheckLibWithHeader to control whether to append or prepend (issue #2767)
+      Also added "unique" keyword, to control whether a library is added
+      or not if it is already in the $LIBS construction var in the
+      configure context. (issue #2768).
 
 
 RELEASE 4.4.0 -  Sat, 30 Jul 2022 14:08:29 -0700
diff --git a/RELEASE.txt b/RELEASE.txt
index 01bf63b12..b68432df3 100644
--- a/RELEASE.txt
+++ b/RELEASE.txt
@@ -46,9 +46,11 @@ CHANGED/ENHANCED EXISTING FUNCTIONALITY
 - Preliminary support for Python 3.12.
 - Run LaTeX after biber/bibtex only if necessary
 - Configure context methods CheckLib and CheckLibWithHeader now expose
-  an additional keyword argument 'append' which controls whether to append
-  (the default) or prepend discovered libraries to $LIBS.  The functionality
-  was always present but prepending could not be requested via the offical API.
+  two additional keyword arguments: 'append', which controls whether to append
+  (the default) or prepend discovered libraries to $LIBS, and 'unique',
+  which controls whether to add the library if it is already in the $LIBS
+  list. This brings the library-adding functionality in Configure in line
+  with the regular Append, AppendUnique, Prepend and PrependUnique methods.
 
 
 FIXES
diff --git a/SCons/Conftest.py b/SCons/Conftest.py
index 83175cb2c..3c52ef462 100644
--- a/SCons/Conftest.py
+++ b/SCons/Conftest.py
@@ -267,7 +267,7 @@ def CheckFunc(context, function_name, header = None, language = None):
 #ifdef __cplusplus
 extern "C"
 #endif
-char %s();""" % function_name
+char %s(void);""" % function_name
 
     lang, suffix, msg = _lang2suffix(language)
     if msg:
@@ -285,7 +285,7 @@ char %s();""" % function_name
 
 int main(void) {
 #if defined (__stub_%(name)s) || defined (__stub___%(name)s)
-  fail fail fail
+  #error "%(name)s has a GNU stub, cannot check"
 #else
   %(name)s();
 #endif
@@ -627,7 +627,7 @@ int main(void) {
 
 def CheckLib(context, libs, func_name = None, header = None,
              extra_libs = None, call = None, language = None, autoadd = 1,
-             append = True):
+             append=True, unique=False):
     """
     Configure check for a C or C++ libraries "libs".  Searches through
     the list of libraries, until one is found where the test succeeds.
@@ -713,9 +713,9 @@ return 0;
             if extra_libs:
                 l.extend(extra_libs)
             if append:
-                oldLIBS = context.AppendLIBS(l)
+                oldLIBS = context.AppendLIBS(l, unique)
             else:
-                oldLIBS = context.PrependLIBS(l)
+                oldLIBS = context.PrependLIBS(l, unique)
             sym = "HAVE_LIB" + lib_name
         else:
             oldLIBS = -1
diff --git a/SCons/SConf.py b/SCons/SConf.py
index 051c14ce6..85edd3ab1 100644
--- a/SCons/SConf.py
+++ b/SCons/SConf.py
@@ -923,14 +923,20 @@ class CheckContext:
         st, out = self.TryRun(text, ext)
         return not st, out
 
-    def AppendLIBS(self, lib_name_list):
+    def AppendLIBS(self, lib_name_list, unique=False):
         oldLIBS = self.env.get( 'LIBS', [] )
-        self.env.Append(LIBS = lib_name_list)
+        if unique:
+            self.env.AppendUnique(LIBS = lib_name_list)
+        else:
+            self.env.Append(LIBS = lib_name_list)
         return oldLIBS
 
-    def PrependLIBS(self, lib_name_list):
+    def PrependLIBS(self, lib_name_list, unique=False):
         oldLIBS = self.env.get( 'LIBS', [] )
-        self.env.Prepend(LIBS = lib_name_list)
+        if unique:
+            self.env.PrependUnique(LIBS = lib_name_list)
+        else:
+            self.env.Prepend(LIBS = lib_name_list)
         return oldLIBS
 
     def SetLIBS(self, val):
@@ -1067,7 +1073,8 @@ def CheckCXXHeader(context, header, include_quotes = '""'):
 
 
 def CheckLib(context, library = None, symbol = "main",
-             header = None, language = None, autoadd=True, append=True,) -> bool:
+             header = None, language = None, autoadd=True,
+             append=True, unique=False) -> bool:
     """
     A test for a library. See also CheckLibWithHeader.
     Note that library may also be None to test whether the given symbol
@@ -1083,7 +1090,7 @@ def CheckLib(context, library = None, symbol = "main",
     # ToDo: accept path for the library
     res = SCons.Conftest.CheckLib(context, library, symbol, header = header,
                                         language = language, autoadd = autoadd,
-                                        append=append)
+                                        append=append, unique=unique)
     context.did_show_result = True
     return not res
 
@@ -1091,7 +1098,7 @@ def CheckLib(context, library = None, symbol = "main",
 # Bram: Can only include one header and can't use #ifdef HAVE_HEADER_H.
 
 def CheckLibWithHeader(context, libs, header, language,
-                       call = None, autoadd=True, append=True) -> bool:
+                       call = None, autoadd=True, append=True, unique=False) -> bool:
     # ToDo: accept path for library. Support system header files.
     """
     Another (more sophisticated) test for a library.
@@ -1108,7 +1115,8 @@ def CheckLibWithHeader(context, libs, header, language,
         libs = [libs]
 
     res = SCons.Conftest.CheckLib(context, libs, None, prog_prefix,
-            call = call, language = language, autoadd=autoadd, append=append)
+            call = call, language = language, autoadd=autoadd,
+            append=append, unique=unique)
     context.did_show_result = 1
     return not res
 
diff --git a/SCons/SConfTests.py b/SCons/SConfTests.py
index 172fba75c..f0290e51c 100644
--- a/SCons/SConfTests.py
+++ b/SCons/SConfTests.py
@@ -32,6 +32,7 @@ import TestCmd
 
 sys.stdout = io.StringIO()
 
+# a library that is sure to exist on the platform
 if sys.platform == 'win32':
     existing_lib = "msvcrt"
 else:
@@ -78,9 +79,13 @@ class SConfTestCase(unittest.TestCase):
         #    - cygwin on Windows (using cmd.exe, not bash)
         #    - posix
         #    - msvc on Windows (hopefully)
-        if (not self.scons_env.Detect( self.scons_env.subst('$CXX') ) or
-            not self.scons_env.Detect( self.scons_env.subst('$CC') ) or
-            not self.scons_env.Detect( self.scons_env.subst('$LINK') )):
+        if not all(
+            (
+                self.scons_env.Detect(self.scons_env.subst('$CXX')),
+                self.scons_env.Detect(self.scons_env.subst('$CC')),
+                self.scons_env.Detect(self.scons_env.subst('$LINK')),
+            )
+        ):
             raise Exception("This test needs an installed compiler!")
         if self.scons_env['CXX'] == 'g++':
             global existing_lib
@@ -502,27 +507,59 @@ int main(void) {
             r = sconf.CheckLib( ["hopefullynolib",existing_lib], "main", autoadd=0 )
             assert r, "did not find %s " % existing_lib
 
-            # CheckLib() with autoadd
             def libs(env):
                 return env.get('LIBS', [])
 
-            env = sconf.env.Clone()
-
+            # CheckLib() with combinations of autoadd, append
             try:
-                r = sconf.CheckLib( existing_lib, "main", autoadd=1 )
+                env = sconf.env.Clone()
+                r = sconf.CheckLib(existing_lib, "main", autoadd=True, append=True)
                 assert r, "did not find main in %s" % existing_lib
                 expect = libs(env) + [existing_lib]
                 got = libs(sconf.env)
                 assert got == expect, "LIBS: expected %s, got %s" % (expect, got)
 
+                env = sconf.env.Clone()
+                r = sconf.CheckLib(existing_lib, "main", autoadd=True, append=False)
+                assert r, "did not find main in %s" % existing_lib
+                expect = [existing_lib] + libs(env)
+                got = libs(sconf.env)
+                assert got == expect, "LIBS: expected %s, got %s" % (expect, got)
+
                 sconf.env = env.Clone()
-                r = sconf.CheckLib( existing_lib, "main", autoadd=0 )
+                r = sconf.CheckLib(existing_lib, "main", autoadd=False)
                 assert r, "did not find main in %s" % existing_lib
                 expect = libs(env)
                 got = libs(sconf.env)
                 assert got == expect, "before and after LIBS were not the same"
             finally:
                 sconf.env = env
+
+            # CheckLib() with unique
+            sconf.env.Append(LIBS=existing_lib)
+            try:
+                env = sconf.env.Clone()
+                r = sconf.CheckLib(
+                    existing_lib, "main", autoadd=True, append=True, unique=False
+                )
+                assert r, f"did not find main in {existing_lib}"
+
+                expect = libs(env) + [existing_lib]
+                got = libs(sconf.env)
+                assert got == expect, f"LIBS: expected {expect}, got {got}"
+
+                env = sconf.env.Clone()
+                r = sconf.CheckLib(
+                    existing_lib, "main", autoadd=True, append=True, unique=True
+                )
+                assert r, f"did not find main in {existing_lib}"
+
+                expect = libs(env)
+                got = libs(sconf.env)
+                assert got == expect, f"LIBS: expected {expect}, got {got}"
+            finally:
+                sconf.env = env
+
         finally:
             sconf.Finish()
 
@@ -565,13 +602,12 @@ int main(void) {
             r = sconf.CheckLibWithHeader( [existing_lib,"hopefullynolib"], ["stdio.h", "math.h"], "C", autoadd=0 )
             assert r, "did not find %s, #include stdio.h first" % existing_lib
 
-            # CheckLibWithHeader with autoadd
             def libs(env):
                 return env.get('LIBS', [])
 
-            env = sconf.env.Clone()
-
+            # CheckLibWithHeader with combinations of autoadd, append
             try:
+                env = sconf.env.Clone()
                 r = sconf.CheckLibWithHeader(
                     existing_lib, "math.h", "C", autoadd=True, append=True
                 )
@@ -600,6 +636,29 @@ int main(void) {
             finally:
                 sconf.env = env
 
+            # CheckLibWithHeader() with unique
+            sconf.env.Append(LIBS=existing_lib)
+            try:
+                env = sconf.env.Clone()
+                r = sconf.CheckLibWithHeader(
+                    existing_lib, "math.h", "C", autoadd=True, append=True, unique=False
+                )
+                assert r, f"did not find main in {existing_lib}"
+                expect = libs(env) + [existing_lib]
+                got = libs(sconf.env)
+                assert got == expect, f"LIBS: expected {expect}, got {got}"
+
+                env = sconf.env.Clone()
+                r = sconf.CheckLibWithHeader(
+                    existing_lib, "math.h", "C", autoadd=True, append=True, unique=True
+                )
+                assert r, f"did not find main in {existing_lib}"
+                expect = libs(env)
+                got = libs(sconf.env)
+                assert got == expect, f"LIBS: expected {expect}, got {got}"
+            finally:
+                sconf.env = env
+
         finally:
             sconf.Finish()
 
diff --git a/doc/man/scons.xml b/doc/man/scons.xml
index 15270e2d9..e79a267d1 100644
--- a/doc/man/scons.xml
+++ b/doc/man/scons.xml
@@ -3892,7 +3892,7 @@ Returns a boolean indicating success or failure.</para>
   <term><replaceable>context</replaceable>.<methodname>CheckFunc</methodname>(<parameter>function_name, [header, language]</parameter>)</term>
   <listitem>
 <para>Checks if <parameter>function_name</parameter> is usable
-in the context's local environment using the compiler
+in the context's local environment, using the compiler
 specified by <parameter>language</parameter> - that is,
 can a check referencing it be compiled using the current values
 of &cv-link-CFLAGS;, &cv-link-CPPFLAGS;,
@@ -3913,17 +3913,21 @@ If omitted, the default stanza will be
 #ifdef __cplusplus
 extern "C"
 #endif
-char function_name();
+char function_name(void);
 </programlisting>
 
 <para>
-Note: do not use <parameter>header</parameter>
-to include the standard header file that declares
-<parameter>function_name</parameter> - successful
-compilation of the test program depends on using
-a dummy prototype for it,
-to avoid probems with compilers which object to
-function signature mismatches.
+Note: if <parameter>header</parameter> is supplied,
+it should <emphasis>not</emphasis>
+include the standard header file that declares
+<parameter>function_name</parameter>,
+and it <emphasis>should</emphasis> include a
+dummy prototype similar to the default case.
+Compilers reject builds where a function call does
+not match the declared prototype as happens
+if the "real" header is included,
+and modern compilers are now rejecting
+implicit function declarations.
 </para>
 
 <para>Returns a boolean indicating success or failure.</para>
@@ -3931,7 +3935,7 @@ function signature mismatches.
   </varlistentry>
 
   <varlistentry>
-  <term><replaceable>context</replaceable>.<methodname>CheckLib</methodname>(<parameter>[library, symbol, header, language, autoadd=True, append=True]</parameter>) </term>
+  <term><replaceable>context</replaceable>.<methodname>CheckLib</methodname>(<parameter>[library, symbol, header, language, autoadd=True, append=True, unique=False]</parameter>) </term>
   <listitem>
 <para>Checks if
 <parameter>library</parameter>
@@ -3948,12 +3952,17 @@ linking the stub program),
 it is added to the &cv-link-LIBS; &consvar; in the context.
 if <parameter>append</parameter> is true (the default),
 the library is appended, otherwise it is prepended.
+If <parameter>unique</parameter> is true,
+and the library would otherwise be added but is
+already present in &cv-link-LIBS; in the configure context,
+it will not be added again. The default is <literal>False</literal>.
 </para>
 <para>
 <parameter>library</parameter> can be a list of library names,
 or <constant>None</constant> (the default if the argument is omitted).
 If the former, <parameter>symbol</parameter> is checked against
-each library name in order, returning on the first
+each library name in order, returning 
+(and reporting success) on the first
 successful test; if the latter,
 it is checked with the current value of &cv-LIBS;
 (in this case no library name would be added).
@@ -3973,13 +3982,14 @@ at least one should be supplied.
 <para>Returns a boolean indicating success or failure.</para>
 <para>
 <emphasis>Changed in version 4.5.0: added the
-<parameter>append</parameter> parameter.</emphasis>
+<parameter>append</parameter> and <parameter>unique</parameter>
+parameters.</emphasis>
 </para>
   </listitem>
   </varlistentry>
 
   <varlistentry>
-  <term><replaceable>context</replaceable>.<methodname>CheckLibWithHeader</methodname>(<parameter>library, header, [language, call, autoadd=True, append=True]</parameter>)</term>
+  <term><replaceable>context</replaceable>.<methodname>CheckLibWithHeader</methodname>(<parameter>library, header, [language, call, autoadd=True, append=True, unique=False]</parameter>)</term>
   <listitem>
 
 <para>Provides an alternative to the
@@ -4012,11 +4022,16 @@ is added to the &cv-link-LIBS; &consvar; in the context
 and the method returns.
 If <parameter>append</parameter> is true (the default),
 the library is appended, otherwise prepended.
+If <parameter>unique</parameter> is true,
+and the library would otherwise be added but is
+already present in &cv-link-LIBS; in the configure context,
+it will not be added again. The default is <literal>False</literal>.
 </para>
 <para>Returns a boolean indicating success or failure.</para>
 <para>
 <emphasis>Changed in version 4.5.0: added the
-<parameter>append</parameter> parameter.</emphasis>
+<parameter>append</parameter> and <parameter>unique</parameter>
+parameters.</emphasis>
 </para>
   </listitem>
   </varlistentry>