feat(path): add commonprefix

Author: haithium

spec/path_spec.lua

@@ -55,6 +55,27 @@ local tests = {
     {{ [[C:\a\b]]        }, { "C:/a/b"        }},
     {{ [[\\srv\share\a]] }, { "//srv/share/a" }},
   },
+  commonprefix = {
+    "common",
+    {{{                                           }}, { ""                }},
+    {{{ ""                  , "abc"               }}, { ""                }},
+    {{{ "abc"               , "abd"               }}, { "ab"              }},
+    {{{ "Xbcd"              , "Xb"                }}, { "Xb"              }},
+    {{{ "abcX"              , "abcd"              }}, { "abc"             }},
+    {{{ "aXc"               , "aX"                }}, { "aX"              }},
+    {{{ "abc"               , "abc"               }}, { "abc"             }},
+    {{{ "abc"               , "xbc"               }}, { ""                }},
+    {{{ "/a/b"              , "/a/c"              }}, { "/a/"             }},
+    {{{ "/home/swenson/spam", "/home/swen/spam"   }}, { "/home/swen"      }},
+    {{{ "/home/swen/spam"   , "/home/swen/eggs"   }}, { "/home/swen/"     }},
+    {{{ "/home/swen/spam"   , "/home/swen/spam"   }}, { "/home/swen/spam" }},
+    {{{ "home:swenson:spam" , "home:swen:spam"    }}, { "home:swen"       }},
+    {{{ ":home:swen:spam"   , ":home:swen:eggs"   }}, { ":home:swen:"     }},
+    {{{ ":home:swen:spam"   , ":home:swen:spam"   }}, { ":home:swen:spam" }},
+    {{{ "/home/swen/spam"   , "/home/swen/spam"   }}, { "/home/swen/spam" }},
+    "windows",
+    {{{ [[\home\swen\spam]] , [[\home\swen\eggs]] }}, { [[\home\swen\]]   }},
+  },
   dirnames = {
     "posix",
     {{ "a/b/c"        }, {{ "a/b"      , "a"       , "." }}},

src/mods/path.lua

@@ -169,6 +169,32 @@ function M.drive(p)
   return (splitroot(p))
 end
 
+function M.commonprefix(paths)
+  assert_arg(1, paths, "table")
+  if #paths == 0 then
+    return ""
+  end
+
+  local min_path = paths[1]
+  local max_path = paths[1]
+  for i = 1, #paths do
+    local path_ = paths[i]
+    assert_arg(i, path_, "string")
+    if path_ < min_path then
+      min_path = path_
+    elseif path_ > max_path then
+      max_path = path_
+    end
+  end
+
+  local i = 1
+  local n = #min_path
+  while i <= n and sub(min_path, i, i) == sub(max_path, i, i) do
+    i = i + 1
+  end
+  return sub(min_path, 1, i - 1)
+end
+
 function M.expandvars(p)
   assert_arg(1, p, "string")
   local res = expandvars(getenv, p, "%${([^}]*)}", "${", "}")

types/path.lua

@@ -272,6 +272,20 @@ function M.relpath(path, start) end
 ---@nodiscard
 function M.commonpath(paths) end
 
+---
+---Return longest common leading string prefix.
+---
+---```lua
+---path.commonprefix({"abc", "abd"})                         --> "ab"
+---path.commonprefix({"/home/swen/spam", "/home/swen/eggs"}) --> "/home/swen/"
+---path.commonprefix({"abc", "xyz"})                         --> ""
+---```
+---
+---@param paths string[] List of paths.
+---@return string commonPrefix Longest common string prefix.
+---@nodiscard
+function M.commonprefix(paths) end
+
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