Add 'nix log' manpage

src/nix/log.cc

@@ -13,22 +13,11 @@ struct CmdLog : InstallableCommand
         return "show the build log of the specified packages or paths, if available";
     }
 
-    Examples examples() override
+    std::string doc() override
     {
-        return {
-            Example{
-                "To get the build log of GNU Hello:",
-                "nix log nixpkgs#hello"
-            },
-            Example{
-                "To get the build log of a specific path:",
-                "nix log /nix/store/lmngj4wcm9rkv3w4dfhzhcyij3195hiq-thunderbird-52.2.1"
-            },
-            Example{
-                "To get a build log from a specific binary cache:",
-                "nix log --store https://cache.nixos.org nixpkgs#hello"
-            },
-        };
+        return
+          #include "log.md"
+          ;
     }
 
     Category category() override { return catSecondary; }

src/nix/log.md

@@ -0,0 +1,40 @@
+R""(
+
+# Examples
+
+* Get the build log of GNU Hello:
+
+  ```console
+  # nix log nixpkgs#hello
+  ```
+
+* Get the build log of a specific store path:
+
+  ```console
+  # nix log /nix/store/lmngj4wcm9rkv3w4dfhzhcyij3195hiq-thunderbird-52.2.1
+  ```
+
+* Get a build log from a specific binary cache:
+
+  ```console
+  # nix log --store https://cache.nixos.org nixpkgs#hello
+  ```
+
+# Description
+
+This command prints the log of a previous build of a derivation on
+standard output.
+
+Nix looks for build logs in two places:
+
+* In the directory `/nix/var/log/nix/drvs`, which contains logs for
+  locally built derivations.
+
+* In the binary caches listed in the `substituters` setting. Logs
+  should be named `<cache>/log/<base-name-of-store-path>`, where
+  `store-path` is a derivation,
+  e.g. `https://cache.nixos.org/log/dvmig8jgrdapvbyxb1rprckdmdqx08kv-hello-2.10.drv`.
+  For non-derivation store paths, Nix will first try to determine the
+  deriver by fetching the `.narinfo` file for this store path.
+
+)""