solver3: Add const where helpful

operator[] is a bit annoying here, but oh well, what can we
do?

2 files changed, 24 insertions, 10 deletions

diff --git a/apt-pkg/solver3.cc b/apt-pkg/solver3.cc
index f402d1ba3..36bdd9aeb 100644
--- a/apt-pkg/solver3.cc
+++ b/apt-pkg/solver3.cc
@@ -229,7 +229,7 @@ bool APT::Solver::Work::operator<(APT::Solver::Work const &b) const
    return false;
 }
 
-std::string APT::Solver::Clause::toString(pkgCache &cache)
+std::string APT::Solver::Clause::toString(pkgCache &cache) const
 {
    std::string out;
    if (auto Pkg = reason.Pkg(cache); not Pkg.end())
@@ -242,7 +242,7 @@ std::string APT::Solver::Clause::toString(pkgCache &cache)
    return out;
 }
 
-std::string APT::Solver::Work::toString(pkgCache &cache)
+std::string APT::Solver::Work::toString(pkgCache &cache) const
 {
    std::ostringstream out;
    if (erased)
@@ -255,7 +255,7 @@ std::string APT::Solver::Work::toString(pkgCache &cache)
 }
 
 // Prints an implication graph part of the form A -> B -> C, possibly with "not"
-std::string APT::Solver::WhyStr(Var reason)
+std::string APT::Solver::WhyStr(Var reason) const
 {
    std::vector<std::string> out;
 
@@ -997,7 +997,7 @@ bool APT::Solver::FromDepCache(pkgDepCache &depcache)
    return Propagate();
 }
 
-bool APT::Solver::ToDepCache(pkgDepCache &depcache)
+bool APT::Solver::ToDepCache(pkgDepCache &depcache) const
 {
    pkgDepCache::ActionGroup group(depcache);
    for (auto P = cache.PkgBegin(); not P.end(); P++)
diff --git a/apt-pkg/solver3.h b/apt-pkg/solver3.h
index bbe3f3d56..9059552b7 100644
--- a/apt-pkg/solver3.h
+++ b/apt-pkg/solver3.h
@@ -105,14 +105,23 @@ class Solver
    {
       return pkgStates[P->ID];
    }
+   inline const State &operator[](pkgCache::Package *P) const
+   {
+      return pkgStates[P->ID];
+   }
 
    // \brief Helper function for safe access to version state.
    inline State &operator[](pkgCache::Version *V)
    {
       return verStates[V->ID];
    }
+   inline const State &operator[](pkgCache::Version *V) const
+   {
+      return verStates[V->ID];
+   }
    // \brief Helper function for safe access to either state.
    inline State &operator[](Var r);
+   inline const State &operator[](Var r) const;
 
    mutable std::vector<char> pkgObsolete;
    bool Obsolete(pkgCache::PkgIterator pkg) const;
@@ -221,13 +230,13 @@ class Solver
    // \brief Apply the selections from the dep cache to the solver
    [[nodiscard]] bool FromDepCache(pkgDepCache &depcache);
    // \brief Apply the solver result to the depCache
-   [[nodiscard]] bool ToDepCache(pkgDepCache &depcache);
+   [[nodiscard]] bool ToDepCache(pkgDepCache &depcache) const;
 
    // \brief Solve the dependencies
    [[nodiscard]] bool Solve();
 
    // Print dependency chain
-   std::string WhyStr(Var reason);
+   std::string WhyStr(Var reason) const;
 };
 
 }; // namespace APT
@@ -319,7 +328,7 @@ struct APT::Solver::Clause
 
    inline Clause(Var reason, Group group, bool optional = false, bool negative = false) : reason(reason), group(group), optional(optional), negative(negative) {}
 
-   std::string toString(pkgCache &cache);
+   std::string toString(pkgCache &cache) const;
 };
 
 /**
@@ -334,7 +343,7 @@ struct APT::Solver::Clause
  */
 struct APT::Solver::Work
 {
-   Clause *clause;
+   const Clause *clause;
 
    // \brief The depth at which the item has been added
    depth_type depth;
@@ -353,8 +362,8 @@ struct APT::Solver::Work
    bool erased{false};
 
    bool operator<(APT::Solver::Work const &b) const;
-   std::string toString(pkgCache &cache);
-   inline Work(Clause *clause, depth_type depth) : clause(clause), depth(depth) {}
+   std::string toString(pkgCache &cache) const;
+   inline Work(const Clause *clause, depth_type depth) : clause(clause), depth(depth) {}
 };
 
 // \brief This essentially describes the install state in RFC2119 terms.
@@ -429,3 +438,8 @@ inline APT::Solver::State &APT::Solver::operator[](Var r)
       return (*this)[cache.VerP + V];
    return *rootState.get();
 }
+
+inline const APT::Solver::State &APT::Solver::operator[](Var r) const
+{
+   return const_cast<Solver &>(*this)[r];
+}