libexpr: stop lying about DrvInfo's constness

DrvInfo's query methods all use mutable fields to cache, but like.
that's basically the entire interface for DrvInfo. Not only that, but
these formerly-const-marked functions can even throw due to eval errors!
Changing this only required removing some `const` markers in nix-env,
and changing a single inline `queryInstalled()` call to be an lvalue
instead.

Change-Id: I796807118f3b35b0e93668b5e28210d9e521b2ae

2 files changed, 17 insertions, 17 deletions

diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index 8c8e142b8..b199cd09e 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -45,7 +45,7 @@ DrvInfo::DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPat
 }
 
 
-std::string DrvInfo::queryName() const
+std::string DrvInfo::queryName()
 {
     if (name == "" && attrs) {
         auto i = attrs->find(state->sName);
@@ -56,7 +56,7 @@ std::string DrvInfo::queryName() const
 }
 
 
-std::string DrvInfo::querySystem() const
+std::string DrvInfo::querySystem()
 {
     if (system == "" && attrs) {
         auto i = attrs->find(state->sSystem);
@@ -66,7 +66,7 @@ std::string DrvInfo::querySystem() const
 }
 
 
-std::optional<StorePath> DrvInfo::queryDrvPath() const
+std::optional<StorePath> DrvInfo::queryDrvPath()
 {
     if (!drvPath && attrs) {
         Bindings::iterator i = attrs->find(state->sDrvPath);
@@ -80,7 +80,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath() const
 }
 
 
-StorePath DrvInfo::requireDrvPath() const
+StorePath DrvInfo::requireDrvPath()
 {
     if (auto drvPath = queryDrvPath())
         return *drvPath;
@@ -88,7 +88,7 @@ StorePath DrvInfo::requireDrvPath() const
 }
 
 
-StorePath DrvInfo::queryOutPath() const
+StorePath DrvInfo::queryOutPath()
 {
     if (!outPath && attrs) {
         Bindings::iterator i = attrs->find(state->sOutPath);
@@ -164,7 +164,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
 }
 
 
-std::string DrvInfo::queryOutputName() const
+std::string DrvInfo::queryOutputName()
 {
     if (outputName == "" && attrs) {
         Bindings::iterator i = attrs->find(state->sOutputName);
diff --git a/src/libexpr/get-drvs.hh b/src/libexpr/get-drvs.hh
index 584d64ac1..d620eca63 100644
--- a/src/libexpr/get-drvs.hh
+++ b/src/libexpr/get-drvs.hh
@@ -19,11 +19,11 @@ public:
 private:
     EvalState * state;
 
-    mutable std::string name;
-    mutable std::string system;
-    mutable std::optional<std::optional<StorePath>> drvPath;
-    mutable std::optional<StorePath> outPath;
-    mutable std::string outputName;
+    std::string name;
+    std::string system;
+    std::optional<std::optional<StorePath>> drvPath;
+    std::optional<StorePath> outPath;
+    std::string outputName;
     Outputs outputs;
 
     /**
@@ -47,12 +47,12 @@ public:
     DrvInfo(EvalState & state, std::string attrPath, Bindings * attrs);
     DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPathWithOutputs);
 
-    std::string queryName() const;
-    std::string querySystem() const;
-    std::optional<StorePath> queryDrvPath() const;
-    StorePath requireDrvPath() const;
-    StorePath queryOutPath() const;
-    std::string queryOutputName() const;
+    std::string queryName();
+    std::string querySystem();
+    std::optional<StorePath> queryDrvPath();
+    StorePath requireDrvPath();
+    StorePath queryOutPath();
+    std::string queryOutputName();
     /**
      * Return the unordered map of output names to (optional) output paths.
      * The "outputs to install" are determined by `meta.outputsToInstall`.