group inherit by source during Expr::show

for plain inherits this is really just a stylistic choice, but for
inherit-from it actually fixes an exponential size increase problem
during expr printing (as may happen during assertion failure reporting,
on during duplicate attr detection in the parser)

(cherry picked from commit ecf8b12d60ad2929f9998666cf0966475b91e291)
Change-Id: Ie55f0cb01a37e766414c31f8d40f51c2c7d106b0

3 files changed, 31 insertions, 5 deletions

diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index 525b2440b..c9d42cea5 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -77,10 +77,36 @@ void ExprAttrs::showBindings(const SymbolTable & symbols, std::ostream & str) co
         std::string_view sa = symbols[a->first], sb = symbols[b->first];
         return sa < sb;
     });
+    std::vector<Symbol> inherits;
+    std::map<Expr *, std::vector<Symbol>> inheritsFrom;
     for (auto & i : sorted) {
-        if (i->second.inherited())
-            str << "inherit " << symbols[i->first] << " " << "; ";
-        else {
+        switch (i->second.kind) {
+        case AttrDef::Kind::Plain:
+            break;
+        case AttrDef::Kind::Inherited:
+            inherits.push_back(i->first);
+            break;
+        case AttrDef::Kind::InheritedFrom: {
+            auto & select = dynamic_cast<ExprSelect &>(*i->second.e);
+            inheritsFrom[select.e].push_back(i->first);
+            break;
+        }
+        }
+    }
+    if (!inherits.empty()) {
+        str << "inherit";
+        for (auto sym : inherits) str << " " << symbols[sym];
+        str << "; ";
+    }
+    for (const auto & [from, syms] : inheritsFrom) {
+        str << "inherit (";
+        from->show(symbols, str);
+        str << ")";
+        for (auto sym : syms) str << " " << symbols[sym];
+        str << "; ";
+    }
+    for (auto & i : sorted) {
+        if (i->second.kind == AttrDef::Kind::Plain) {
             str << symbols[i->first] << " = ";
             i->second.e->show(symbols, str);
             str << "; ";
diff --git a/tests/functional/lang/parse-okay-inherits.exp b/tests/functional/lang/parse-okay-inherits.exp
index 722101ceb..1355527e6 100644
--- a/tests/functional/lang/parse-okay-inherits.exp
+++ b/tests/functional/lang/parse-okay-inherits.exp
@@ -1 +1 @@
-(let b = 2; c = { }; in { a = 1; inherit b ; d = (c).d; e = (c).e; f = 3; })
+(let b = 2; c = { }; in { inherit b; inherit (c) d e; a = 1; f = 3; })
diff --git a/tests/functional/lang/parse-okay-subversion.exp b/tests/functional/lang/parse-okay-subversion.exp
index 4168ee8bf..2303932c4 100644
--- a/tests/functional/lang/parse-okay-subversion.exp
+++ b/tests/functional/lang/parse-okay-subversion.exp
@@ -1 +1 @@
-({ fetchurl, localServer ? false, httpServer ? false, sslSupport ? false, pythonBindings ? false, javaSwigBindings ? false, javahlBindings ? false, stdenv, openssl ? null, httpd ? null, db4 ? null, expat, swig ? null, j2sdk ? null }: assert (expat != null); assert (localServer -> (db4 != null)); assert (httpServer -> ((httpd != null) && ((httpd).expat == expat))); assert (sslSupport -> ((openssl != null) && (httpServer -> ((httpd).openssl == openssl)))); assert (pythonBindings -> ((swig != null) && (swig).pythonSupport)); assert (javaSwigBindings -> ((swig != null) && (swig).javaSupport)); assert (javahlBindings -> (j2sdk != null)); ((stdenv).mkDerivation { builder = /foo/bar; db4 = (if localServer then db4 else null); inherit expat ; inherit httpServer ; httpd = (if httpServer then httpd else null); j2sdk = (if javaSwigBindings then (swig).j2sdk else (if javahlBindings then j2sdk else null)); inherit javaSwigBindings ; inherit javahlBindings ; inherit localServer ; name = "subversion-1.1.1"; openssl = (if sslSupport then openssl else null); patches = (if javahlBindings then [ (/javahl.patch) ] else [ ]); python = (if pythonBindings then (swig).python else null); inherit pythonBindings ; src = (fetchurl { md5 = "a180c3fe91680389c210c99def54d9e0"; url = "http://subversion.tigris.org/tarballs/subversion-1.1.1.tar.bz2"; }); inherit sslSupport ; swig = (if (pythonBindings || javaSwigBindings) then swig else null); }))
+({ fetchurl, localServer ? false, httpServer ? false, sslSupport ? false, pythonBindings ? false, javaSwigBindings ? false, javahlBindings ? false, stdenv, openssl ? null, httpd ? null, db4 ? null, expat, swig ? null, j2sdk ? null }: assert (expat != null); assert (localServer -> (db4 != null)); assert (httpServer -> ((httpd != null) && ((httpd).expat == expat))); assert (sslSupport -> ((openssl != null) && (httpServer -> ((httpd).openssl == openssl)))); assert (pythonBindings -> ((swig != null) && (swig).pythonSupport)); assert (javaSwigBindings -> ((swig != null) && (swig).javaSupport)); assert (javahlBindings -> (j2sdk != null)); ((stdenv).mkDerivation { inherit expat httpServer javaSwigBindings javahlBindings localServer pythonBindings sslSupport; builder = /foo/bar; db4 = (if localServer then db4 else null); httpd = (if httpServer then httpd else null); j2sdk = (if javaSwigBindings then (swig).j2sdk else (if javahlBindings then j2sdk else null)); name = "subversion-1.1.1"; openssl = (if sslSupport then openssl else null); patches = (if javahlBindings then [ (/javahl.patch) ] else [ ]); python = (if pythonBindings then (swig).python else null); src = (fetchurl { md5 = "a180c3fe91680389c210c99def54d9e0"; url = "http://subversion.tigris.org/tarballs/subversion-1.1.1.tar.bz2"; }); swig = (if (pythonBindings || javaSwigBindings) then swig else null); }))