fix #13222: make relativePath more robust and flexible (#13451)

* * relativePath(foo) now works
* relativePath(rel, abs) and relativePath(abs, rel) now work (fixes #13222)
* relativePath, absolutePath, getCurrentDir now available in more targets (eg: vm, nodejs etc)
* fix bug: isAbsolutePath now works with -d:js; add tests
* workaround https://github.com/nim-lang/Nim/issues/13469
* remove `relativePath(path)` overload for now
* add back changelog after rebase

1 files changed, 90 insertions, 68 deletions

diff --git a/lib/pure/os.nim b/lib/pure/os.nim
index e1e5f31b4..2c3e91be8 100644
--- a/lib/pure/os.nim
+++ b/lib/pure/os.nim
@@ -98,6 +98,8 @@ type
 
 include "includes/osseps"
 
+proc absolutePathInternal(path: string): string {.gcsafe.}
+
 proc normalizePathEnd(path: var string, trailingSep = false) =
   ## Ensures ``path`` has exactly 0 or 1 trailing `DirSep`, depending on
   ## ``trailingSep``, and taking care of edge cases: it preservers whether
@@ -297,8 +299,12 @@ proc isAbsolute*(path: string): bool {.rtl, noSideEffect, extern: "nos$1", raise
     result = path[0] != ':'
   elif defined(RISCOS):
     result = path[0] == '$'
-  elif defined(posix):
+  elif defined(posix) or defined(js):
+    # `or defined(js)` wouldn't be needed pending https://github.com/nim-lang/Nim/issues/13469
+    # This works around the problem for posix, but windows is still broken with nim js -d:nodejs
     result = path[0] == '/'
+  else:
+    doAssert false # if ever hits here, adapt as needed
 
 when FileSystemCaseSensitive:
   template `!=?`(a, b: char): bool = a != b
@@ -360,8 +366,8 @@ when doslikeFileSystem:
         else:
           return false
 
-proc relativePath*(path, base: string; sep = DirSep): string {.
-  noSideEffect, rtl, extern: "nos$1", raises: [].} =
+proc relativePath*(path, base: string, sep = DirSep): string {.
+  rtl, extern: "nos$1".} =
   ## Converts `path` to a path relative to `base`.
   ##
   ## The `sep` (default: `DirSep <#DirSep>`_) is used for the path normalizations,
@@ -390,6 +396,12 @@ proc relativePath*(path, base: string; sep = DirSep): string {.
   var path = path
   path.normalizePathAux
   base.normalizePathAux
+  let a1 = isAbsolute(path)
+  let a2 = isAbsolute(base)
+  if a1 and not a2:
+    base = absolutePathInternal(base)
+  elif a2 and not a1:
+    path = absolutePathInternal(path)
 
   when doslikeFileSystem:
     if isAbsolute(path) and isAbsolute(base):
@@ -1293,60 +1305,67 @@ proc fileNewer*(a, b: string): bool {.rtl, extern: "nos$1", noNimScript.} =
   else:
     result = getLastModificationTime(a) > getLastModificationTime(b)
 
-proc getCurrentDir*(): string {.rtl, extern: "nos$1", tags: [], noNimScript.} =
-  ## Returns the `current working directory`:idx: i.e. where the built
-  ## binary is run.
-  ##
-  ## So the path returned by this proc is determined at run time.
-  ##
-  ## See also:
-  ## * `getHomeDir proc <#getHomeDir>`_
-  ## * `getConfigDir proc <#getConfigDir>`_
-  ## * `getTempDir proc <#getTempDir>`_
-  ## * `setCurrentDir proc <#setCurrentDir,string>`_
-  ## * `currentSourcePath template <system.html#currentSourcePath.t>`_
-  ## * `getProjectPath proc <macros.html#getProjectPath>`_
-  when defined(windows):
-    var bufsize = MAX_PATH.int32
-    when useWinUnicode:
-      var res = newWideCString("", bufsize)
-      while true:
-        var L = getCurrentDirectoryW(bufsize, res)
-        if L == 0'i32:
-          raiseOSError(osLastError())
-        elif L > bufsize:
-          res = newWideCString("", L)
-          bufsize = L
-        else:
-          result = res$L
-          break
+when not defined(nimscript):
+  proc getCurrentDir*(): string {.rtl, extern: "nos$1", tags: [].} =
+    ## Returns the `current working directory`:idx: i.e. where the built
+    ## binary is run.
+    ##
+    ## So the path returned by this proc is determined at run time.
+    ##
+    ## See also:
+    ## * `getHomeDir proc <#getHomeDir>`_
+    ## * `getConfigDir proc <#getConfigDir>`_
+    ## * `getTempDir proc <#getTempDir>`_
+    ## * `setCurrentDir proc <#setCurrentDir,string>`_
+    ## * `currentSourcePath template <system.html#currentSourcePath.t>`_
+    ## * `getProjectPath proc <macros.html#getProjectPath>`_
+    when defined(nodejs):
+      var ret: cstring
+      {.emit: "`ret` = process.cwd();".}
+      return $ret
+    elif defined(js):
+      doAssert false, "use -d:nodejs to have `getCurrentDir` defined"
+    elif defined(windows):
+      var bufsize = MAX_PATH.int32
+      when useWinUnicode:
+        var res = newWideCString("", bufsize)
+        while true:
+          var L = getCurrentDirectoryW(bufsize, res)
+          if L == 0'i32:
+            raiseOSError(osLastError())
+          elif L > bufsize:
+            res = newWideCString("", L)
+            bufsize = L
+          else:
+            result = res$L
+            break
+      else:
+        result = newString(bufsize)
+        while true:
+          var L = getCurrentDirectoryA(bufsize, result)
+          if L == 0'i32:
+            raiseOSError(osLastError())
+          elif L > bufsize:
+            result = newString(L)
+            bufsize = L
+          else:
+            setLen(result, L)
+            break
     else:
+      var bufsize = 1024 # should be enough
       result = newString(bufsize)
       while true:
-        var L = getCurrentDirectoryA(bufsize, result)
-        if L == 0'i32:
-          raiseOSError(osLastError())
-        elif L > bufsize:
-          result = newString(L)
-          bufsize = L
-        else:
-          setLen(result, L)
+        if getcwd(result, bufsize) != nil:
+          setLen(result, c_strlen(result))
           break
-  else:
-    var bufsize = 1024 # should be enough
-    result = newString(bufsize)
-    while true:
-      if getcwd(result, bufsize) != nil:
-        setLen(result, c_strlen(result))
-        break
-      else:
-        let err = osLastError()
-        if err.int32 == ERANGE:
-          bufsize = bufsize shl 1
-          doAssert(bufsize >= 0)
-          result = newString(bufsize)
         else:
-          raiseOSError(osLastError())
+          let err = osLastError()
+          if err.int32 == ERANGE:
+            bufsize = bufsize shl 1
+            doAssert(bufsize >= 0)
+            result = newString(bufsize)
+          else:
+            raiseOSError(osLastError())
 
 proc setCurrentDir*(newDir: string) {.inline, tags: [], noNimScript.} =
   ## Sets the `current working directory`:idx:; `OSError`
@@ -1366,23 +1385,26 @@ proc setCurrentDir*(newDir: string) {.inline, tags: [], noNimScript.} =
   else:
     if chdir(newDir) != 0'i32: raiseOSError(osLastError(), newDir)
 
-when not weirdTarget:
-  proc absolutePath*(path: string, root = getCurrentDir()): string {.noNimScript.} =
-    ## Returns the absolute path of `path`, rooted at `root` (which must be absolute;
-    ## default: current directory).
-    ## If `path` is absolute, return it, ignoring `root`.
-    ##
-    ## See also:
-    ## * `normalizedPath proc <#normalizedPath,string>`_
-    ## * `normalizePath proc <#normalizePath,string>`_
-    runnableExamples:
-      assert absolutePath("a") == getCurrentDir() / "a"
 
-    if isAbsolute(path): path
-    else:
-      if not root.isAbsolute:
-        raise newException(ValueError, "The specified root is not absolute: " & root)
-      joinPath(root, path)
+proc absolutePath*(path: string, root = getCurrentDir()): string =
+  ## Returns the absolute path of `path`, rooted at `root` (which must be absolute;
+  ## default: current directory).
+  ## If `path` is absolute, return it, ignoring `root`.
+  ##
+  ## See also:
+  ## * `normalizedPath proc <#normalizedPath,string>`_
+  ## * `normalizePath proc <#normalizePath,string>`_
+  runnableExamples:
+    assert absolutePath("a") == getCurrentDir() / "a"
+
+  if isAbsolute(path): path
+  else:
+    if not root.isAbsolute:
+      raise newException(ValueError, "The specified root is not absolute: " & root)
+    joinPath(root, path)
+
+proc absolutePathInternal(path: string): string =
+  absolutePath(path, getCurrentDir())
 
 proc normalizePath*(path: var string) {.rtl, extern: "nos$1", tags: [].} =
   ## Normalize a path.