add discard_from() function

this function discards all values that come from a specific file. it
will be needed for configure bootstrapping, but is too obscure to
document it for general use.

Change-Id: I62c18aeb1847712e33d0599dbb0b90ffa1722438
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from qtbase/12bb328bb0be8efe54aae750c21938aab4d17539)

src/shared/proparser/qmakebuiltins.cpp

@@ -47,6 +47,8 @@
 # include <qthreadpool.h>
 #endif
 
+#include <algorithm>
+
 #ifdef Q_OS_UNIX
 #include <time.h>
 #include <utime.h>
@@ -92,7 +94,7 @@ enum ExpandFunc {
 enum TestFunc {
     T_INVALID = 0, T_REQUIRES, T_GREATERTHAN, T_LESSTHAN, T_EQUALS,
     T_EXISTS, T_EXPORT, T_CLEAR, T_UNSET, T_EVAL, T_CONFIG, T_SYSTEM,
-    T_DEFINED, T_CONTAINS, T_INFILE,
+    T_DEFINED, T_DISCARD_FROM, T_CONTAINS, T_INFILE,
     T_COUNT, T_ISEMPTY, T_PARSE_JSON, T_INCLUDE, T_LOAD, T_DEBUG, T_LOG, T_MESSAGE, T_WARNING, T_ERROR, T_IF,
     T_MKPATH, T_WRITE_FILE, T_TOUCH, T_CACHE
 };
@@ -173,6 +175,7 @@ void QMakeEvaluator::initFunctionStatics()
         { "if", T_IF },
         { "isActiveConfig", T_CONFIG },
         { "system", T_SYSTEM },
+        { "discard_from", T_DISCARD_FROM },
         { "defined", T_DEFINED },
         { "contains", T_CONTAINS },
         { "infile", T_INFILE },
@@ -1288,6 +1291,38 @@ QMakeEvaluator::VisitReturn QMakeEvaluator::evaluateBuiltinConditional(
         }
         return ReturnTrue;
     }
+    case T_DISCARD_FROM: {
+        if (args.count() != 1 || args.at(0).isEmpty()) {
+            evalError(fL1S("discard_from(file) requires one argument."));
+            return ReturnFalse;
+        }
+        if (m_valuemapStack.count() != 1) {
+            evalError(fL1S("discard_from() cannot be called from functions."));
+            return ReturnFalse;
+        }
+        QString fn = resolvePath(args.at(0).toQString(m_tmp1));
+        ProFile *pro = m_parser->parsedProFile(fn, QMakeParser::ParseOnlyCached);
+        if (!pro)
+            return ReturnFalse;
+        ProValueMap &vmap = m_valuemapStack.first();
+        for (auto vit = vmap.begin(); vit != vmap.end(); ) {
+            if (!vit->isEmpty()) {
+                auto isFrom = [pro](const ProString &s) {
+                    return s.sourceFile() == pro;
+                };
+                vit->erase(std::remove_if(vit->begin(), vit->end(), isFrom), vit->end());
+                if (vit->isEmpty()) {
+                    // When an initially non-empty variable becomes entirely empty,
+                    // undefine it altogether.
+                    vit = vmap.erase(vit);
+                    continue;
+                }
+            }
+            ++vit;
+        }
+        pro->deref();
+        return ReturnTrue;
+    }
     case T_INFILE:
         if (args.count() < 2 || args.count() > 3) {
             evalError(fL1S("infile(file, var, [values]) requires two or three arguments."));

src/shared/proparser/qmakeparser.cpp

@@ -162,7 +162,7 @@ QMakeParser::QMakeParser(ProFileCache *cache, QMakeVfs *vfs, QMakeParserHandler
 ProFile *QMakeParser::parsedProFile(const QString &fileName, ParseFlags flags)
 {
     ProFile *pro;
-    if ((flags & ParseUseCache) && m_cache) {
+    if ((flags & (ParseUseCache|ParseOnlyCached)) && m_cache) {
         ProFileCache::Entry *ent;
 #ifdef PROPARSER_THREAD_SAFE
         QMutexLocker locker(&m_cache->mutex);
@@ -184,7 +184,7 @@ ProFile *QMakeParser::parsedProFile(const QString &fileName, ParseFlags flags)
 #endif
             if ((pro = ent->pro))
                 pro->ref();
-        } else {
+        } else if (!(flags & ParseOnlyCached)) {
             ent = &m_cache->parsed_files[fileName];
 #ifdef PROPARSER_THREAD_SAFE
             ent->locker = new ProFileCache::Entry::Locker;
@@ -209,13 +209,17 @@ ProFile *QMakeParser::parsedProFile(const QString &fileName, ParseFlags flags)
                 ent->locker = 0;
             }
 #endif
-        }
         } else {
+            pro = 0;
+        }
+    } else if (!(flags & ParseOnlyCached)) {
         pro = new ProFile(fileName);
         if (!read(pro, flags)) {
             delete pro;
             pro = 0;
         }
+    } else {
+        pro = 0;
     }
     return pro;
 }

src/shared/proparser/qmakeparser.h

@@ -74,7 +74,8 @@ public:
     enum ParseFlag {
         ParseDefault = 0,
         ParseUseCache = 1,
-        ParseReportMissing = 2
+        ParseOnlyCached = 2,
+        ParseReportMissing = 4
     };
     Q_DECLARE_FLAGS(ParseFlags, ParseFlag)