Three changes to nx2/build.py:

- A4: a link whose inputs are the last successful one's is not run again
  (run_link). Its key, beside the output as <output>.linkkey: the command,
  the compiler and the work folder's system-headers stamp, each object's
  key (.o.sha1), and the contents of the other files it names, inside
  options too (the hot symbol order). A build with nothing to do went from
  16 s to 6 s on Windows. Players' builds let sa/build go, so it helps a
  work folder that keeps its files (the checkout's work/,
  LONGSHOT_KEEP_BUILD_FILES=1).
- A8: <build>/compile_commands.json, every compile as compile_one runs it,
  for clangd and clang-tidy (git-ignored at the checkout's top).
- The hot pieces' keys name the play profile by its contents
  (-DLONGSHOT_PROFILE_SHA1), not its path: a build from a checkout other
  than the work folder's compiled all eight again (~10-20 minutes). This
  changes their keys once.

tests/test_link_skip.py (a stand-in linker: skipped, relinked on a changed
object, library, symbol order or output, a failed link forgets the key;
the compile commands) and tests/test_profile_path_key.py.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

@@ -38,2 +38,4 @@
 # ---- NVIDIA's DLSS SDK (scripts/ngx_sdk.py): NVIDIA's files, never committed ----
 ngx-sdk/
+
+# ---- nx2/dev.py compdb: the last build's compile commands, for clangd and clang-tidy ----

@@ -134,0 +189,4 @@
+            old = f.read().split()
+    except OSError:
+        old = []
+    if key and os.path.exists(output) and old == [key, str(os.path.getsize(output))]:

@@ -134,0 +208,4 @@
+    """(the dev-loop proposal's A8) <build>/compile_commands.json: every compile this build runs, as compile_one runs it, for clangd
+    and clang-tidy (nx2/dev.py compdb puts it at the checkout's top). The lifted code's and the host's commands name the lift's
+    gen/ and rt64/ folders, which are this build's; a failure to write it is no failed build"""
+    entries = [{"directory": os.getcwd(), "file": src, "output": obj, "arguments": [cc] + list(fl) + ["-c", src, "-o", obj]}

@@ -667,0 +756,4 @@
+        elif f.startswith("-fprofile-instr-use="):
+            # (the play profile's path: its contents are in -DLONGSHOT_PROFILE_SHA1 beside it. Its path kept two checkouts, or a
+            # build from a checkout other than the work folder's, from sharing the eight hot pieces, ~10-20 minutes to compile)
+            f = "-fprofile-instr-use=<profile>"

@@ -0,0 +109,4 @@
+        main = src[src.index("\ndef main("):]
+        self.assertLess(main.index("write_compdb(out, jobs)"), main.index("plan_jobs(jobs)"))
+        one = src[src.index("\ndef compile_one("):src.index("\ndef ", src.index("\ndef compile_one(") + 1)]
+        self.assertIn('[cc] + fl + ["-c", src, "-o", obj]', one)   # (the command the database says, as compile_one runs it)