bzlmod: support go.mod replace directives with a version qualifier on…

… the left (bazel-contrib#1679)

* support replace directives with a version qualifier on the left

* guard: we do not support local replacements with a from_version

* make it clear that we are keying off of from_path

internal/bzlmod/go_deps.bzl

@@ -341,6 +341,14 @@ def _go_deps_impl(module_ctx):
     # in the module resolutions and swapping out the entry.
     for path, replace in replace_map.items():
         if path in module_resolutions:
+
+            # If the replace directive specified a version then we only
+            # apply it if the versions match.
+            if replace.from_version:
+                comparable_from_version = semver.to_comparable(replace.from_version)
+                if module_resolutions[path].version != comparable_from_version:
+                    continue
+
             new_version = semver.to_comparable(replace.version)
             module_resolutions[path] = with_replaced_or_new_fields(
                 module_resolutions[path],

internal/bzlmod/go_mod.bzl

@@ -141,16 +141,32 @@ def _parse_directive(state, directive, tokens, comment, path, line_no):
     elif directive == "replace":
         # A replace directive might use a local file path beginning with ./ or ../
         # These are not supported with gazelle~go_deps.
-        if len(tokens) == 3 and tokens[2][0] == ".":
+        if (len(tokens) == 3 and tokens[2][0] == ".") or (len(tokens) > 3 and tokens[3][0] == "."):
             fail("{}:{}: local file path not supported in replace directive: '{}'".format(path, line_no, tokens[2]))
 
-        if len(tokens) != 4 or tokens[1] != "=>":
-            fail("{}:{}: replace directive must follow pattern: 'replace from_path => to_path version' ".format(path, line_no))
+        # replacements key off of the from_path
         from_path = tokens[0]
-        state["replace"][from_path] = struct(
-            to_path = tokens[2],
-            version = _canonicalize_raw_version(tokens[3]),
-        )
+
+        # pattern: replace from_path => to_path to_version
+        if len(tokens) == 4 and tokens[1] == "=>":
+            state["replace"][from_path] = struct(
+                from_version = None,
+                to_path = tokens[2],
+                version = _canonicalize_raw_version(tokens[3]),
+            )
+        # pattern: replace from_path from_version => to_path to_version
+        elif len(tokens) == 5 and tokens[2] == "=>":
+            state["replace"][from_path] = struct(
+                from_version = _canonicalize_raw_version(tokens[1]),
+                to_path = tokens[3],
+                version = _canonicalize_raw_version(tokens[4]),
+            )
+        else:
+            fail(
+                "{}:{}: replace directive must follow pattern: ".format(path, line_no) + 
+                "'replace from_path from_version => to_path to_version' or " +
+                "'replace from_path => to_path to_version'"
+            )
 
     # TODO: Handle exclude.
 

tests/bzlmod/go_mod_test.bzl

@@ -13,6 +13,7 @@ github.com/bmatcuk/doublestar/v4 v4.0.2 // indirect
 )
 
 replace github.com/go-fsnotify/fsnotify => github.com/fsnotify/fsnotify v1.4.2
+replace github.com/bmatcuk/doublestar/v4 v4.0.2 => github.com/bmatcuk/doublestar/v4 v4.0.3
 
 module github.com/bazelbuild/bazel-gazelle
 
@@ -28,7 +29,10 @@ require golang.org/x/sys v0.0.0-20220624220833-87e55d714810 // indirect
 _EXPECTED_GO_MOD_PARSE_RESULT = struct(
     go = (1, 18),
     module = "github.com/bazelbuild/bazel-gazelle",
-    replace_map = {"github.com/go-fsnotify/fsnotify": struct(to_path = "github.com/fsnotify/fsnotify", version = "1.4.2")},
+    replace_map = {
+        "github.com/go-fsnotify/fsnotify": struct(from_version = None, to_path = "github.com/fsnotify/fsnotify", version = "1.4.2"),
+        "github.com/bmatcuk/doublestar/v4": struct(from_version = "4.0.2", to_path = "github.com/bmatcuk/doublestar/v4", version = "4.0.3"),
+    },
     require = (
         struct(indirect = False, path = "github.com/bazelbuild/buildtools", version = "v0.0.0-20220531122519-a43aed7014c8"),
         struct(indirect = False, path = "github.com/bazelbuild/rules_go", version = "v0.n\\\"33.0"),