src/libcmd/repl.cc: allow :log /path/to/store.drv

This adds a second form to the `:log` command: it now can accept a
derivation path in addition to a derivation expression. As derivation
store paths start with `/nix/store`, this is not ambiguous.

Resolves: https://git.lix.systems/lix-project/lix/issues/51
Change-Id: Iebc7b011537e7012fae8faed4024ea1b8fdc81c3

doc/manual/rl-next/repl-log-drv.md

@@ -0,0 +1,9 @@
+---
+synopsis: "`:log` in repl now works on derivation paths"
+issues: [fj#51]
+cls: [1716]
+category: Improvements
+credits: [goldstein]
+---
+
+`:log` can now accept store derivation paths in addition to derivation expressions.

src/libcmd/repl.cc

@@ -536,7 +536,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
              << "  :t <expr>                    Describe result of evaluation\n"
              << "  :u <expr>                    Build derivation, then start nix-shell\n"
              << "  :doc <expr>                  Show documentation for the provided function (experimental lambda support)\n"
-             << "  :log <expr>                  Show logs for a derivation\n"
+             << "  :log <expr | .drv path>      Show logs for a derivation\n"
              << "  :te, :trace-enable [bool]    Enable, disable or toggle showing traces for\n"
              << "                               errors\n"
              << "  :?, :help                    Brings up this help menu\n"
@@ -676,7 +676,49 @@ ProcessLineResult NixRepl::processLine(std::string line)
         runNix("nix-shell", {state->store->printStorePath(drvPath)});
     }
 
-    else if (command == ":b" || command == ":bl" || command == ":i" || command == ":sh" || command == ":log") {
+    else if (command == ":log") {
+        StorePath drvPath = ([&] {
+            auto maybeDrvPath = state->store->maybeParseStorePath(arg);
+            if (maybeDrvPath && maybeDrvPath->isDerivation()) {
+                return std::move(*maybeDrvPath);
+            } else {
+                Value v;
+                evalString(arg, v);
+                return getDerivationPath(v);
+            }
+        })();
+        Path drvPathRaw = state->store->printStorePath(drvPath);
+
+        settings.readOnlyMode = true;
+        Finally roModeReset([&]() {
+            settings.readOnlyMode = false;
+        });
+        auto subs = getDefaultSubstituters();
+
+        subs.push_front(state->store);
+
+        bool foundLog = false;
+        RunPager pager;
+        for (auto & sub : subs) {
+            auto * logSubP = dynamic_cast<LogStore *>(&*sub);
+            if (!logSubP) {
+                printInfo("Skipped '%s' which does not support retrieving build logs", sub->getUri());
+                continue;
+            }
+            auto & logSub = *logSubP;
+
+            auto log = logSub.getBuildLog(drvPath);
+            if (log) {
+                printInfo("got build log for '%s' from '%s'", drvPathRaw, logSub.getUri());
+                logger->writeToStdout(*log);
+                foundLog = true;
+                break;
+            }
+        }
+        if (!foundLog) throw Error("build log of '%s' is not available", drvPathRaw);
+    }
+
+    else if (command == ":b" || command == ":bl" || command == ":i" || command == ":sh") {
         Value v;
         evalString(arg, v);
         StorePath drvPath = getDerivationPath(v);
@@ -712,34 +754,6 @@ ProcessLineResult NixRepl::processLine(std::string line)
             }
         } else if (command == ":i") {
             runNix("nix-env", {"-i", drvPathRaw});
-        } else if (command == ":log") {
-            settings.readOnlyMode = true;
-            Finally roModeReset([&]() {
-                settings.readOnlyMode = false;
-            });
-            auto subs = getDefaultSubstituters();
-
-            subs.push_front(state->store);
-
-            bool foundLog = false;
-            RunPager pager;
-            for (auto & sub : subs) {
-                auto * logSubP = dynamic_cast<LogStore *>(&*sub);
-                if (!logSubP) {
-                    printInfo("Skipped '%s' which does not support retrieving build logs", sub->getUri());
-                    continue;
-                }
-                auto & logSub = *logSubP;
-
-                auto log = logSub.getBuildLog(drvPath);
-                if (log) {
-                    printInfo("got build log for '%s' from '%s'", drvPathRaw, logSub.getUri());
-                    logger->writeToStdout(*log);
-                    foundLog = true;
-                    break;
-                }
-            }
-            if (!foundLog) throw Error("build log of '%s' is not available", drvPathRaw);
         } else {
             runNix("nix-shell", {drvPathRaw});
         }

tests/functional/repl.sh

@@ -271,3 +271,8 @@ a = ''test string that we'll grep later''
 :e identity
 a
 " "undefined variable"
+
+# Test :log with derivation paths.
+simple_path="$(nix-instantiate "$testDir/simple.nix")"
+# `PATH=` is a part of build log.
+testReplResponseNoRegex ":log ${simple_path}" "PATH="