From dfa2f77d2e1118f32771c2fceefd683435554b9d Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Tue, 8 Apr 2014 19:24:29 +0200
Subject: If a .drv cannot be parsed, show its path
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Otherwise you just get ‘expected string `Derive(['’ which isn't very helpful.
---
 src/libexpr/primops.cc      |  2 +-
 src/libstore/derivations.cc | 16 +++++++++++++---
 src/libstore/derivations.hh |  4 ++--
 src/libstore/local-store.cc |  4 ++--
 src/libstore/misc.cc        |  2 +-
 src/libutil/util.cc         |  2 +-
 src/libutil/util.hh         |  2 ++
 7 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index b4e75648f8ab..c69d520d3be0 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -67,7 +67,7 @@ static void prim_import(EvalState & state, const Pos & pos, Value * * args, Valu
     }
 
     if (isStorePath(path) && store->isValidPath(path) && isDerivation(path)) {
-        Derivation drv = parseDerivation(readFile(path));
+        Derivation drv = readDerivation(path);
         Value & w = *state.allocValue();
         state.mkAttrs(w, 1 + drv.outputs.size());
         mkString(*state.allocAttr(w, state.sDrvPath), path, singleton<PathSet>("=" + path));
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index d91e42784ca5..b452aa2caf56 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -48,7 +48,7 @@ static Path parsePath(std::istream & str)
 {
     string s = parseString(str);
     if (s.size() == 0 || s[0] != '/')
-        throw Error(format("bad path `%1%' in derivation") % s);
+        throw FormatError(format("bad path `%1%' in derivation") % s);
     return s;
 }
 
@@ -62,7 +62,7 @@ static StringSet parseStrings(std::istream & str, bool arePaths)
 }
 
 
-Derivation parseDerivation(const string & s)
+static Derivation parseDerivation(const string & s)
 {
     Derivation drv;
     std::istringstream str(s);
@@ -112,6 +112,16 @@ Derivation parseDerivation(const string & s)
 }
 
 
+Derivation readDerivation(const Path & drvPath)
+{
+    try {
+        return parseDerivation(readFile(drvPath));
+    } catch (FormatError & e) {
+        throw Error(format("error parsing derivation `%1%': %2%") % drvPath % e.msg());
+    }
+}
+
+
 static void printString(string & res, const string & s)
 {
     res += '"';
@@ -240,7 +250,7 @@ Hash hashDerivationModulo(StoreAPI & store, Derivation drv)
         Hash h = drvHashes[i->first];
         if (h.type == htUnknown) {
             assert(store.isValidPath(i->first));
-            Derivation drv2 = parseDerivation(readFile(i->first));
+            Derivation drv2 = readDerivation(i->first);
             h = hashDerivationModulo(store, drv2);
             drvHashes[i->first] = h;
         }
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 703410b92552..04b64dfc88a7 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -59,8 +59,8 @@ class StoreAPI;
 Path writeDerivation(StoreAPI & store,
     const Derivation & drv, const string & name, bool repair = false);
 
-/* Parse a derivation. */
-Derivation parseDerivation(const string & s);
+/* Read a derivation from a file. */
+Derivation readDerivation(const Path & drvPath);
 
 /* Print a derivation. */
 string unparseDerivation(const Derivation & drv);
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 1293a6e8f260..567706d09748 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -661,7 +661,7 @@ unsigned long long LocalStore::addValidPath(const ValidPathInfo & info, bool che
        efficiently query whether a path is an output of some
        derivation. */
     if (isDerivation(info.path)) {
-        Derivation drv = parseDerivation(readFile(info.path));
+        Derivation drv = readDerivation(info.path);
 
         /* Verify that the output paths in the derivation are correct
            (i.e., follow the scheme for computing output paths from
@@ -1290,7 +1290,7 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
             if (isDerivation(i->path)) {
                 // FIXME: inefficient; we already loaded the
                 // derivation in addValidPath().
-                Derivation drv = parseDerivation(readFile(i->path));
+                Derivation drv = readDerivation(i->path);
                 checkDerivationOutputs(i->path, drv);
             }
 
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 1bf3f9378245..6ecf8787cf61 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -11,7 +11,7 @@ Derivation derivationFromPath(StoreAPI & store, const Path & drvPath)
 {
     assertStorePath(drvPath);
     store.ensurePath(drvPath);
-    return parseDerivation(readFile(drvPath));
+    return readDerivation(drvPath);
 }
 
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 15c462ce4e5b..846674a29d95 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1041,7 +1041,7 @@ void expect(std::istream & str, const string & s)
     char s2[s.size()];
     str.read(s2, s.size());
     if (string(s2, s.size()) != s)
-        throw Error(format("expected string `%1%'") % s);
+        throw FormatError(format("expected string `%1%'") % s);
 }
 
 
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 8bedfea9a0de..ce2d77c19a42 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -326,6 +326,8 @@ bool hasSuffix(const string & s, const string & suffix);
 /* Read string `s' from stream `str'. */
 void expect(std::istream & str, const string & s);
 
+MakeError(FormatError, Error)
+
 
 /* Read a C-style string from stream `str'. */
 string parseString(std::istream & str);
-- 
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