Extract common triple decomposition logic into a helper method that r…

…eturns a struct with the fields populated.

rust/platform/triple_mappings.bzl

@@ -196,6 +196,36 @@ def abi_to_constraints(abi):
         # figure out how they're doing this
         return []
 
+def triple_to_struct(triple):
+    if triple == "wasm32-wasi":
+        return struct(
+            cpu_arch = "wasi",
+            vendor = None,
+            system = "wasi",
+            abi = None,
+        )
+
+    component_parts = triple.split("-")
+    if len(component_parts) < 3:
+        fail("Expected target triple to contain at least three sections separated by '-'")
+
+    cpu_arch = component_parts[0]
+    vendor = component_parts[1]
+    system = component_parts[2]
+    if system == "androideabi":
+        system = "android"
+
+    abi = None
+    if len(component_parts) >= 4:
+        abi = component_parts[3]
+
+    return struct(
+        cpu_arch = cpu_arch,
+        vendor = vendor,
+        system = system,
+        abi = abi,
+    )
+
 def triple_to_system(triple):
     """Returns a system name for a given platform triple
 
@@ -205,17 +235,7 @@ def triple_to_system(triple):
     Returns:
         str: A system name
     """
-    if triple == "wasm32-wasi":
-        return "wasi"
-
-    component_parts = triple.split("-")
-    if len(component_parts) < 3:
-        fail("Expected target triple to contain at least three sections separated by '-'")
-
-    system = component_parts[2]
-    if (system == "androideabi"):
-        system = "android"
-    return system
+    return triple_to_struct(triple).system
 
 def triple_to_arch(triple):
     """Returns a system architecture name for a given platform triple
@@ -226,14 +246,7 @@ def triple_to_arch(triple):
     Returns:
         str: A cpu architecture
     """
-    if triple == "wasm32-wasi":
-        return "wasi"
-
-    component_parts = triple.split("-")
-    if len(component_parts) < 3:
-        fail("Expected target triple to contain at least three sections separated by '-'")
-
-    return component_parts[0]
+    return triple_to_struct(triple).cpu_arch
 
 def triple_to_abi(triple):
     """Returns a system abi name for a given platform triple
@@ -244,13 +257,7 @@ def triple_to_abi(triple):
     Returns:
         str: The triple's abi
     """
-    component_parts = triple.split("-")
-    if len(component_parts) < 3:
-        fail("Expected target triple to contain at least three sections separated by '-'")
-
-    if len(component_parts) >= 4:
-        return component_parts[3]
-    return None
+    triple_to_struct(triple).abi
 
 def system_to_dylib_ext(system):
     return _SYSTEM_TO_DYLIB_EXT[system]
@@ -284,26 +291,12 @@ def triple_to_constraint_set(triple):
             "@rules_rust//rust/platform/os:unknown",
         ]
 
-    component_parts = triple.split("-")
-    if len(component_parts) < 3:
-        fail("Expected target triple to contain at least three sections separated by '-'")
-
-    cpu_arch = component_parts[0]
-    vendor = component_parts[1]
-    system = component_parts[2]
-    abi = None
-
-    if system == "androideabi":
-        system = "android"
-        cpu_arch = "arm"
-
-    if len(component_parts) == 4:
-        abi = component_parts[3]
+    triple_struct = triple_to_struct(triple)
 
     constraint_set = []
-    constraint_set += cpu_arch_to_constraints(cpu_arch)
-    constraint_set += vendor_to_constraints(vendor)
-    constraint_set += system_to_constraints(system)
-    constraint_set += abi_to_constraints(abi)
+    constraint_set += cpu_arch_to_constraints(triple_struct.cpu_arch)
+    constraint_set += vendor_to_constraints(triple_struct.vendor)
+    constraint_set += system_to_constraints(triple_struct.system)
+    constraint_set += abi_to_constraints(triple_struct.abi)
 
     return constraint_set