arglist: De-dup arg prefixes only when they are used as a prefix

This was already done for dedup2_prefixes, also do it for
dedup1_prefixes, and move export-dynamic to dedup1_args, where it
belongs.

Also modify some comments around this to clearly distinguish
standalone argument matching and argument-prefix matching.

Author: nirbheek

mesonbuild/arglist.py

@@ -29,7 +29,7 @@ class Dedup(enum.Enum):
         same is true for include paths and library paths with -I and -L.
     UNIQUE - Arguments that once specified cannot be undone, such as `-c` or
         `-pipe`. New instances of these can be completely skipped.
-    NO_DEDUP - Whether it matters where or how many times on the command-line
+    NO_DEDUP - When it matters where or how many times on the command-line
         a particular argument is present. This can matter for symbol
         resolution in static or shared libraries, so we cannot de-dup or
         reorder them.
@@ -74,12 +74,12 @@ class CompilerArgs(T.MutableSequence[str]):
     # Arg prefixes that override by prepending instead of appending
     prepend_prefixes: T.Tuple[str, ...] = ()
 
-    # Arg prefixes and args that must be de-duped by returning 2
+    # Arg prefixes and standalone args that must be de-duped by returning 2
     dedup2_prefixes: T.Tuple[str, ...] = ()
     dedup2_suffixes: T.Tuple[str, ...] = ()
     dedup2_args: T.Tuple[str, ...] = ()
 
-    # Arg prefixes and args that must be de-duped by returning 1
+    # Arg prefixes and standalone args that must be de-duped by returning 1
     #
     # NOTE: not thorough. A list of potential corner cases can be found in
     # https://github.com/mesonbuild/meson/pull/4593#pullrequestreview-182016038
@@ -193,15 +193,16 @@ def _can_dedup(cls, arg: str) -> Dedup:
         with other linkers.
         """
 
-        # A standalone argument must never be deduplicated because it is
-        # defined by what comes _after_ it. Thus deduping this:
+        # Argument prefixes that are actually not used as a prefix must never
+        # be deduplicated because they are defined by what comes _after_ them.
+        # Thus deduping this:
         # -D FOO -D BAR
         # would yield either
         # -D FOO BAR
         # or
         # FOO -D BAR
         # both of which are invalid.
-        if arg in cls.dedup2_prefixes:
+        if arg in cls.dedup1_prefixes or arg in cls.dedup2_prefixes:
             return Dedup.NO_DEDUP
         if arg in cls.dedup2_args or \
            arg.startswith(cls.dedup2_prefixes) or \

mesonbuild/compilers/mixins/clike.py

@@ -53,9 +53,9 @@ class CLikeCompilerArgs(arglist.CompilerArgs):
 
     # NOTE: not thorough. A list of potential corner cases can be found in
     # https://github.com/mesonbuild/meson/pull/4593#pullrequestreview-182016038
-    dedup1_prefixes = ('-l', '-Wl,-l', '-Wl,--export-dynamic')
+    dedup1_prefixes = ('-l', '-Wl,-l')
     dedup1_suffixes = ('.lib', '.dll', '.so', '.dylib', '.a')
-    dedup1_args = ('-c', '-S', '-E', '-pipe', '-pthread')
+    dedup1_args = ('-c', '-S', '-E', '-pipe', '-pthread', '-Wl,--export-dynamic')
 
     def to_native(self, copy: bool = False) -> T.List[str]:
         # This seems to be allowed, but could never work?